Content uploaded by Phoebe Barnard
Author content
All content in this area was uploaded by Phoebe Barnard on May 05, 2024
Content may be subject to copyright.
Earth at risk: An urgent call to end the age of destruction
and forge a just and sustainable future
Charles Fletcher
a,
*, William J. Ripple
b
, Thomas Newsome
c
, Phoebe Barnard
d,e
, Kamanamaikalani Beamer
f,g
, Aishwarya Behl
a
,
Jay Bowen
h,i
, Michael Cooney
j
, Eileen Crist
k
, Christopher Field
l
, Krista Hiser
m,n
, David M. Karl
o,p
, David A. King
q
,
Michael E. Mann
r
, Davianna P. McGregor
s
, Camilo Mora
t
, Naomi Oreskes
u
and Michael Wilson
v
a
School of Ocean and Earth Science and Technology, University of Hawai‘i at Manoa, Honolulu, HI 96822, USA
b
Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA
c
School of Life and Environmental Sciences, University of Sydney, Sydney, NSW 2006, Australia
d
Center for Environmental Politics and School of Interdisciplinary Arts and Sciences, University of Washington, Seattle, WA 98195, USA
e
African Climate and Development Initiative and FitzPatrick Institute, University of Cape Town, Cape Town 7700, South Africa
f
Hui ‘A
ina Momona Program, Richardson School of Law, University of Hawai‘i at Ma
noa, Honolulu, HI 96822, USA
g
Hawai‘inuia
kea School of Hawaiian Knowledge, Kamakaku
okalani Center for Hawaiian Studies, University of Hawai‘i at Ma
noa, Honolulu, HI 96822, USA
h
Institute of American Indian Arts, Santa Fe, NM 87508, USA
i
Upper Skagit Tribe, Sedro Woolley, WA 98284, USA
j
School of Ocean and Earth Science and Technology, Hawai‘i Natural Energy Institute, University of Hawai‘i at Ma
noa, Honolulu, HI 96822, USA
k
Department of Science Technology and Society, Virginia Tech, Blacksburg, VA 24060, USA
l
Doerr School for Sustainability, Stanford Woods Institute for the Environment, Stanford University, Stanford, CA 94305, USA
m
Department of Languages, Linguistics, and Literature, Kapi‘olani Community College, Honolulu, HI 96816, USA
n
Global Council for Science and the Environment, Washington, DC 20006, USA
o
Department of Oceanography, School of Ocean and Earth Science and Technology, Honolulu, HI 96822, USA
p
Daniel K. Inouye Center for Microbial Oceanography, Research and Education, University of Hawai‘i at Manoa, Honolulu, HI 96822, USA
q
Department of Chemistry, University of Cambridge, Cambridge CB2 1DQ, UK
r
Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, PA 19104, USA
s
Department of Ethnic Studies, Center for Oral History, University of Hawai‘i at Ma
noa, Honolulu, HI 96822, USA
t
Department of Geography and Environment, University of Hawai‘i at Manoa, Honolulu, HI 96822, USA
u
Department of the History of Science, Harvard University, Cambridge, MA 02138, USA
v
Associate Justice, Hawaii Supreme Court (retired), Honolulu, HI 96813, USA
*To whom correspondence should be addressed: Email: etcher@apps.soest.hawaii.edu
Edited By: Junguo Liu
Abstract
Human development has ushered in an era of converging crises: climate change, ecological destruction, disease, pollution, and
socioeconomic inequality. This review synthesizes the breadth of these interwoven emergencies and underscores the urgent need for
comprehensive, integrated action. Propelled by imperialism, extractive capitalism, and a surging population, we are speeding past
Earth’s material limits, destroying critical ecosystems, and triggering irreversible changes in biophysical systems that underpin the
Holocene climatic stability which fostered human civilization. The consequences of these actions are disproportionately borne by
vulnerable populations, further entrenching global inequities. Marine and terrestrial biomes face critical tipping points, while
escalating challenges to food and water access foreshadow a bleak outlook for global security. Against this backdrop of Earth at risk,
we call for a global response centered on urgent decarbonization, fostering reciprocity with nature, and implementing regenerative
practices in natural resource management. We call for the elimination of detrimental subsidies, promotion of equitable human
development, and transformative nancial support for lower income nations. A critical paradigm shift must occur that replaces
exploitative, wealth-oriented capitalism with an economic model that prioritizes sustainability, resilience, and justice. We advocate a
global cultural shift that elevates kinship with nature and communal well-being, underpinned by the recognition of Earth’s nite
resources and the interconnectedness of its inhabitants. The imperative is clear: to navigate away from this precipice, we must
collectively harness political will, economic resources, and societal values to steer toward a future where human progress does not
come at the cost of ecological integrity and social equity.
Keywords: environmental policy, global economics, climate change, biodiversity loss, socioeconomic inequality
Competing Interest: The authors declare no competing interest.
© The Author(s) 2024. Published by Oxford University Press on behalf of National Academy of Sciences. This is an Open Access article
distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits
unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Climate change and global sustainability
It is unequivocal that human inuence has warmed the atmos-
phere (1) and the climate crisis is now well underway. Global
greenhouse gas (GHG) emissions set a new record in 2023 (2), rising
an estimated 1.1%, the third annual increase in a row since the
COVID-19 recession. With a record 1.45 ± 0.12°C of anthropogenic
global heating reached in 2023 (3), we already see nearly one-third
of the world population exposed to deadly heat waves (4), a 9-fold
PNAS Nexus, 2024, 3, 1–20
https://doi.org/10.1093/pnasnexus/pgae106
Advance access publication 2 April 2024
Review
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
increase in large North American wildres (5), record-setting
regional-scale megadrought (6), the Antarctic ice sheet losing
nearly 75% more ice between 2011 and 2020 than it did for the pe-
riod 2001 and 2010 (7), animal and plant extinctions projected to
increase 2- to 5-fold in coming decades (8), deepening genetic di-
versity loss (9), and a weakened global ecosystem (10) pushed to
its breaking point (11).
Scientists suspect the last several years have been warmer
than any point in more than 125,000 years (12). Yet demand for
oil climbed to over 100 million barrels per day in 2023, the highest
in history (13). Despite decades of global investment in clean en-
ergy (14), fossil fuels still provide over 80% of global energy use
(15), a gure that has not changed for decades. In the absence of
climate action, our world is on course (16) to heat a blistering
3°C, perhaps more (17), potentially displacing one-third of hu-
manity (18).
One study (19) suggests that ∼9% of people (>600 million) al-
ready live outside the human climate “niche.” Another concludes
that, compared with people born in 1960, children born today will
experience 7.5 times as many heatwaves, 3.6 times as many
droughts, 3 times as many crop failures, 2.8 times as many river
oods, and 2 times as many wildres (20). Studies (21) forecast
climate-related extinction of 14–32% of macroscopic species in
the next ∼50 years, including 3–6 million animal and plant spe-
cies, even under intermediate climate change scenarios. With
continued warming, the frequency of wildres will increase over
74% of the global landmass by the end of this century (22). Such
assessments are conservative as they are based on projections
from climate models that may not capture some important proc-
esses through which human-caused heating amplies persistent
weather extremes (23, 24).
Of the 40 leading economies, all of which agreed in the 2015
Paris Climate Accord to take all necessary actions to stop global
heating below 1.5°C, not one nation is on track to do what they
promised (25). Globally, current climate policies are incompatible
with limiting global heating to 1.5°C (26). The remaining budget
for a 50% chance of keeping warming to 1.5°C is approximately
250 GtCO
2
as of January 2023, now equal to around 6 years of cur-
rent emissions (27). The energy plans of countries responsible for
the largest GHG emissions would lead to 460% more coal produc-
tion, 83% more natural gas, and 29% more oil in 2030 than is com-
patible with limiting global heating to 1.5°C, and 69% more fossil
fuels than is compatible with the riskier 2°C target (28).
The market cost of oil, coal, and natural gas is distorted by subsid-
ies and does not include negative externalities related to pollution,
climate change, healthcare, and others (29). Worse, the false prom-
ise (30) and widespread allure of unregulated quick xes, such as
“net-zero” contracts that lack monitoring, auditing, and verication,
threaten to derail even the best-intentioned commercial and gov-
ernmental plans for climate stabilization (31). Investigations suggest
that the great majority of products transacted on carbon offset mar-
kets remove very little GHG from the atmosphere (32), and models
indicate that even direct removal of atmospheric CO
2
does not re-
cover former environmental conditions crucial to food and water se-
curity or ecosystem restoration (33).
We do not promote a “doom and gloom” philosophy regarding
the future of human civilization. We are optimistic that humanity
can correct the unsustainable pathway that we are on. Later in this
review, we describe necessary steps in this direction. However, we
do take an objective and realistic stand on the issue of sustainabil-
ity. The realities described here quantify a severe and immediate
threat to human health and well-being. They emphasize the im-
perative for a rapid, sweeping reduction in GHG emissions, and
highlight stubborn barriers that impede progress. Developed na-
tions, emerging economies, and commercial entities must invest
in rapid decarbonization; correct market distortions favoring fossil
fuels; and avoid the spurious trap of false “net-zero” offsets as an
excuse to continue polluting the atmosphere.
Imperialism, overpopulation, and resource
extraction
Around the world, a growing number of entities and environmen-
tal activists are taking action (34). As of December 2022, there
have been 2,180 climate-related legal cases led in 65 jurisdic-
tions, including international and regional courts, tribunals, qua-
sijudicial bodies, or other adjudicatory bodies. Lawsuits related to
climate change have more than doubled over the last 5 years as
litigants see courts as a way to enhance (or delay) climate action
(35). Children and youth, women’s groups, local communities,
and Indigenous Peoples, among others, are taking a prominent
role in bringing these cases and driving climate change govern-
ance reform around the world. This “climate justice movement”
seeks to extend the principles of human rights and environmental
justice by arguing that future generations have a birthright to a
safe climate capable of sustaining genuine human development
on a healthy and resilient planet (36).
Yet, for hundreds of years, various manifestations of imperial-
ism, such as slavery, settler colonization, economic and cultural
dominance, neocolonialism (37), and the forces of globalization,
have promoted a mindset of class privilege and wealth.
Motivated by prot, the mechanisms of industrial capitalism
have pursued relentless resource depletion achieved by subjuga-
tion of local communities, erasure of Indigenous knowledge, and
unsustainable plunder of the natural world (38).
Modern imperialism is embodied by industrial capitalism,
which prioritizes resource extraction and maximizing prot.
This paradigm is deeply embedded in the fabric of global affairs,
inuencing international trade, political dynamics, and the eco-
nomic frameworks of nations (39). The persistent reliance on
extractive economic practices continues to be a signicant obs-
tacle to making critical progress in decarbonization, conserving
natural resources, and ensuring social equity. For instance, des-
pite decades of international commitments to end deforestation,
around 4.1 M hectares of primary tropical rainforest was lost glo-
bally in 2022—an increase of 10% over 2021—producing 2.7 Gt of
CO
2
emissions, equivalent to the annual fossil fuel emissions of
India (40). Most modern socioeconomic systems still follow ex-
tractive rules of exploitation and trade, and ignore natural rates
of resource renewal, failing to consider that the end result is cata-
strophic (41).
Global population growth amplies the damage wrought by in-
dustrial capitalism. On 15 November 2022, the world’s population
reached 8 billion people. Human population is expected to in-
crease by nearly 2 billion in the next 30 years, and could peak at
nearly 10.4 billion in the mid-2080s (42). Cambridge economist
Sir Partha Dasgupta developed a rigorous approach to the ques-
tion “What is optimal human population?” (43). His theory relates
population, consumption, and resource capacity, concluding that
an optimal global population lies between 0.5 and 5 billion. This
theory implies that Earth is already overpopulated relative to eco-
logical carrying capacity. With every additional person added to
the planet, wild habitats are disturbed or destroyed by urbanism,
agricultural activities, and resource consumption, with humanity
demanding more than what the biosphere can sustainably
provide.
2 | PNAS Nexus, 2024, Vol. 3, No. 4
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
Dasgupta highlights the critical connection between our econ-
omies, livelihoods, and well-being with the Earth’s resources. He
argues that current global demand for natural resources sur-
passes its capacity to supply, driven by factors like population
growth and consumption patterns. This overuse threatens bio-
diversity and ecosystem services. To safeguard our prosperity
and the environment, we must rethink our approach to economic
success. Key recommendations include increasing nature’s cap-
acity and ensuring our demands on nature stay within sustainable
limits. This involves investing in natural capital, revising econo-
mic metrics, transforming institutions (especially nance and
education), and empowering citizens. Legitimate sustainability
is vital for achieving a long-term balance between population,
economic growth, and the environment. Future generations’ well-
being hinges on how we manage economic, social, and natural re-
sources today. Urgent action is required to address these intercon-
nected challenges.
Given the current state of the ecosphere, a 25% increase in
population and projected doubling of economic activity by
2050 (44) may drive major ecological regime shifts (i.e. forest to
savannah, savannah to desert, thawing tundra, and others)
well before 2080. Nature may impose its own population correc-
tion before standard projections are realized (45). Actions to slow
and reverse population growth are critical (46). These include
empowering women, investing in girls’ education, strengthening
healthcare systems, and implementing social welfare programs
that create job opportunities, reduce poverty, and improve living
standards.
Human population growth, increased economic demands, ris-
ing heat, and extreme weather events put pressures on ecosys-
tems and landscapes to supply food and maintain services such
as clean water. Studies show that ecosystems threatened by sud-
den regime shifts are at greater risk of collapse than previously
thought (47). Researchers warn that more than a fth of ecosys-
tems worldwide, including the Amazon rainforest, are at risk of
a catastrophic breakdown within a human lifetime.
The United Nations’ Sustainable Development Goals (SDGs), a
suite of 17 objectives with 169 targets established in 2015 for
achievement by 2030, face a grim forecast: current trends suggest
none of the goals and merely 12% of the targets may be realized
(48). This shortfall underscores the urgent need to dismantle
the entrenched model of resource extraction and wealth concen-
tration, advocating for a paradigm shift toward genuine sustain-
ability and resource regeneration. Such a transformation is
imperative to reverse the tide of biodiversity loss due to overcon-
sumption and to reinstate the security of food and water supplies,
which are foundational for the survival of global populations.
Global economics and values
Convergence of worldwide trends threatens safe and sustainable
human development: accelerating impacts from climate change
(49), biodiversity loss (50) caused by unsustainable consumption
(51), extractive agriculture, natural resource exploitation (52)
and limitations, emergent disease (53), pervasive pollution (54),
and socioeconomic injustice (55). To secure a safe future for hu-
manity, global economics and values must protect the well-being
of the natural world. This requires understanding the impacts, in-
tersections and feedbacks of these global emergencies, as well as
solutions to ensure a livable planet (56). These emergencies, pro-
mulgated by extractive policies (57), human population growth,
and modern imperialism (58), overlap in ways that amplify nega-
tive outcomes (Fig. 1). If successive governments treat these issues
in isolation, hesitate, or formulate shallow responses, the fallout
may be catastrophic. Without immediate action, we risk entering
a malignant era of global distress and suffering characterized
by disease, thirst and hunger, impoverishment, and political
instability.
The cocoon of wealth enjoyed by developed nations belies the
suffering and misery many low latitude and semiarid communi-
ties already endure in tenuous heat and drought conditions.
Consider the Northern Hemisphere summer of 2023. Over 80%
of the global population experienced climate change-driven heat
in the month of July (59) (Fig. 2). It featured 7 consecutive months
of record-shattering global temperature driven by a combination
of a moderately strong El Niño and a decrease of Earth’s albedo
(equivalent to an increase of atmospheric CO
2
from 420 to
530 ppm) (60). Extreme heatwaves swept many parts of the world.
Sea surface temperatures leapt to record highs. Antarctic sea ice
was far below average. Record wildres burned for months de-
stroying tens of millions of acres and produced continental-scale
public health crises in air quality, and tens of thousands of tem-
perature records around the world were broken. Without human-
induced climate change these events would have been extremely
rare (61).
It is past time to build a new era of reciprocity with nature that
redenes natural resource economics. The ecological contribu-
tions of Indigenous Peoples through their governance institutions
and practices are gaining recognition and interest. Indigenous sys-
tems of land management encompass a holistic approach that
values sacred, ethical, and reciprocal relationships with nature,
integrating traditional knowledge and stewardship principles to
sustainably manage land and water resources. Indigenous land
management challenges conventional power structures and in-
troduces innovative solutions to environmental issues, especially
in the context of climate change.
Indigenous Peoples exercise traditional rights over a quarter of
Earth’s surface, overlapping with a third of intact forests and in-
tersecting about 40% of all terrestrial protected areas and eco-
logically intact landscapes. These lands typically have reduced
deforestation, degradation, and carbon emissions, compared
with nonprotected areas and protected areas (62). Beyond western
ideas of quarantining land for conservation, Indigenous land
management involves a mix of active land management, biomi-
micry, and conservation to maximize nutrition, food and water
security, carbon sequestration, biodiversity, and ecosystem res-
toration (63). These qualities offer benecial feedbacks that in-
crease human health and resiliency, build social equity, and
provide for the needs of future generations.
We suggest that an Indigenous worldview, that of kinship with
nature, should dene sustainable practices. Laws that establish
legal rights for nature have reached a critical point at which
they may either be normalized or marginalized (64); this progress
must be sustained. For instance, Ma
ori in New Zealand have suc-
cessfully asserted sovereignty to grant legal personhood to the
Whanganui River and Te Urewera National Park. This reects
Ma
ori worldviews and recognizes their governance, allowing “na-
ture” to have a legal voice. In the US, the Menominee Forest
Management Reserve, recognized as a best practice, is driven by
the Menominee vision and worldviews. It operates under the
recognition of Menominee sovereignty and decision-making
authority.
Nations must build on these regenerative practices by elimin-
ating environmentally harmful subsidies (65), and restricting
trade that generates pollution and unsustainable consumption.
Studies (66) indicate the global economy must achieve absolute
Fletcher et al. | 3
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
decoupling (in which resource impacts decline in absolute terms)
(67) if we are to eliminate “ecological overshoot”
a
(68).
In the words of coauthor Jay Bowen, Upper Skagit Elder, “We are
all Indigenous to this Earth. We are one family.” The authors of
this review believe that humanity stands at an inection point
in human history that will determine many characteristics of fu-
ture life on Earth (Fig. 3). Continued failure to integrate these prob-
lems in climate resilient development and regenerative practices
risks the stability of human communities and natural systems.
Heads of state must recognize the existence of a global emergency
(56), treat these crises as intertwined issues, and apply the consid-
erable power of the economy toward restoring a livable planet and
an equitable and just socioeconomic system before climate in-
stability and ecological regime shift are beyond our control.
Later in this paper, we offer specic suggestions for implementing
these changes.
Climate realities and the road to action
In April 2023, CO
2
levels measured at Mauna Loa Observatory in
Hawai‘i reached an annual peak of 424.8 ppm, more than 50%
greater than the preindustrial level of 278 ppm. In the rst decade
of measurement at Mauna Loa (1959–1968), the average annual
growth rate was 0.8 ppm per year. The average annual growth
rate over the most recent decade (2014–2023) was 3 times that
amount, 2.4 ppm per year, the fastest sustained rate of increase
in 65 years of monitoring (69).
More than half of all industrial CO
2
emissions have occurred
since 1988 and 40% of the CO
2
we emit today will still be in the at-
mosphere in 100 years, about 20% will still be there in about 1,000
years (70). The last time CO
2
levels were this high was the Pliocene
Climatic Optimum, 4.4 milion years ago, when Earth’s climate was
radically different; global temperature was 2–3°C hotter, beech
Fig. 1. Global population growth, imperialism, and an economic model based on extractive rules of exploitation and trade that ignores natural rates of
resource renewal, set the stage for a convergence of several worldwide trends that threaten safe and sustainable human development: accelerating
impacts from climate change, pollution, social inequality, biodiversity loss, and disease.
4 | PNAS Nexus, 2024, Vol. 3, No. 4
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
trees grew near the South Pole, there was no Greenland ice sheet,
no West Antarctic ice sheet, and global sea level was as much as
25 m higher than today (71).
Atmospheric methane (CH
4
) growth has surged since 2020.
Averaged over 2 decades, the global heating potential of CH
4
is
80 times greater than CO
2
. The largest sources of atmospheric
CH
4
are wetlands, freshwater areas, agriculture, fossil fuel extrac-
tion, landlls, and res. In 2023, atmospheric CH
4
exceeded
1,919 ppb, on track to triple the preindustrial level of 700 ppb by
2030. Carbon isotopic signatures reveal microbial decomposition
of organic matter as the major source of CH
4
emissions, indicating
that natural CH
4
-producing processes are being amplied by
Fig. 2. In 2023, astonishing new records were set in 2 m surface temperature, sea surface temperature (SST), and global sea ice extent (2 m Temperature
World, and SST World after Climate Reanalyzer, Climate Change Institute, University of Maine, https://climatereanalyzer.org/; Global Sea Ice Extent after
https://zacklabe.com/global-sea-ice-extent-conc/).
Fletcher et al. | 5
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
climate change itself (72). Is this a sign that global heating is shift-
ing beyond our control?
Under an intermediate scenario (SSP2-4.5), GHG emissions are
very likely to lead to heating of 1.2–1.8°C in the near term (2021–
2040), 1.6–2.5°C in the midterm (2041–2060), and 2.1–3.5°C in the
long term (2081–2100) (73). As of November 2023, 145 countries
had announced or are considering net-zero targets, covering close
to 90% of global emissions (74). Among these are China, EU, USA,
and India, who jointly represent more than half of global GHG
emissions. However, net-zero evaluations for G20 countries and
selected other countries as of November 2023 show that most net-
zero targets are formulated vaguely and do not yet conform with
good practices.
Even as the vast majority of countries pledged to slash their cli-
mate emissions, their own plans and projections put them on track
to extract more than twice the level of fossil fuels by 2030 than would
be consistent with limiting heating to 1.5°C, and nearly 70% more
than would be consistent with 2°C of heating (28). The world has a
67% chance of limiting warming to 2.9°C if countries stick to the na-
tionally determined contributions (NDCs) made under the 2015 Paris
agreement (26). Emission cuts of 14 GtCO
2
or 28% are needed by 2030
to keep within 2°C of warming. A reduction of more than 40% or
22 GtCO
2
is needed for the 1.5°C threshold to be realistic.
The world now only has a 14% chance of limiting warming to
the 1.5°C goal, even if countries honor all NDCs. Limiting warming
to 1.5°C would require global emission reduction of 8.7% per year.
Even with COVID-19 lockdowns limiting manufacturing, ground
and air transportation, and other economic activities during
2020, emissions dropped by only 4.7% (26).
Many countries’ net-zero pledges “are not currently considered
credible” (26). No G20 country is reducing emissions at a pace con-
sistent with their net-zero targets. The lifetime emissions of cur-
rent and planned oil and gas elds and coal mines is 3 and a
half times greater than the carbon budget needed to hold tem-
perature increase to 1.5°C. It would exhaust almost all the budget
needed for 2°C.
Under current national climate plans, emissions are expected to
rise 9% above 2010 levels by the end of this decade even if NDCs are
fully implemented. GHG emissions would fall to 2% below 2019
levels by 2030. Although these numbers suggest the world will see
emissions peak this decade, that’s still far short of the 43% reduc-
tion against 2019 levels that the Intergovernmental Panel on
Climate Change (IPCC) says is needed to stay within the 1.5°C target
envisioned by the Paris Agreement (26).
Emission reductions of 43% are needed by 2030 to keep 1.5°C in
play. But since the 26th Conference of Parties (COP) in 2021, na-
tions have shaved just 1% off their projected emissions for 2030,
and COP 28 in 2023 ended with no increase in ambition.
Seventy-ve percent of nations that have set targets to limit
GHG emissions have enshrined them in law or policy documents,
but the plans needed to implement those pledges are lacking in al-
most all cases (74), and policies based on “net-zero” actions no lon-
ger have credibility. Current pledges would lead to long-term
global heating of 2.4–2.6°C, but on-the-ground policies put the
world on track for heating approximately 3°C above preindustrial
levels. Avoiding dangerous levels of heating requires systemic
transformation to energy, waste, transportation, agriculture,
and industry.
Climate indicators show that global heating reached 1.14°C
averaged over the past decade, 1.26°C in 2022, and 1.45 ± 0.12°C
over the 12-month period of 2023. In 2023, some 7.3 billion people
worldwide were exposed, for at least 10 days, to temperatures in-
uenced by global warming, with one-quarter of people facing
dangerous levels of extreme heat. Heating is increasing at an un-
precedented rate of over 0.2°C per decade (perhaps faster) caused
by a combination of annual GHG emissions at an all-time high of
54 ± 5.3 GtCO
2
e over the last decade, and reductions in the
strength of aerosol cooling (17). The Northern Hemisphere sum-
mer of 2023 revealed a shift in climate indicators marking a new
level of intensity. “There has never been a summer like this in re-
corded history: shocking ocean heat, deadly land heat, unprece-
dented res and smoke, sea ice melting faster than we’ve ever
seen or thought possible (75).”
Climate outlook
Planned cuts in global emissions are inadequate for protecting
human security and Earth’s remaining biodiversity. Under
HUMAN
VALUES
P
r
o
m
o
t
e
r
e
p
r
o
d
u
c
t
i
v
e
h
e
a
l
t
h
c
a
r
e
,
f
e
m
a
l
e
e
q
u
i
t
y
,
a
n
d
e
d
u
c
a
t
i
o
n
C
o
r
r
e
c
t
m
a
r
k
e
t
d
i
s
t
o
r
t
i
o
n
s
f
a
v
o
r
i
n
g
f
o
s
s
i
l
f
u
e
l
s
R
e
l
i
e
v
e
d
e
b
t
t
o
a
c
c
e
l
e
r
a
t
e
c
l
e
a
n
e
n
e
r
g
y
S
o
c
i
a
l
e
q
u
i
t
y
R
e
c
i
p
r
o
c
i
t
y
w
i
t
h
n
a
t
u
r
e
R
a
p
i
d
d
e
c
a
r
b
o
n
i
z
a
t
i
o
n
I
m
p
l
e
m
e
n
t
r
e
g
e
n
e
r
a
t
i
v
e
p
r
a
c
t
i
c
e
s
E
n
v
i
r
o
n
m
e
n
t
a
l
j
u
s
t
i
c
e
S
o
c
i
o
-
e
c
o
n
o
m
i
c
i
n
e
q
u
a
l
i
t
y
C
l
i
m
a
t
e
c
h
a
n
g
e
B
i
o
d
i
v
e
r
s
i
t
y
l
o
s
s
P
o
l
l
u
t
i
o
n
D
i
s
e
a
s
e
Fig. 3. The stability of human communities and natural ecosystems is at risk under the shocks and stresses of ve planetary emergencies: socioeconomic
inequality, climate change, biodiversity loss, pollution, and disease. Unless human values shift dramatically and soon, the resulting damage to the
natural world will likely be catastrophic, with long-lasting consequences for species and ecosystems, and devastating upheavals for humanity. A
systemic change in human values is needed that focuses on Earth-centered governance, and entails a transition in collective values, behaviors, and
institutional practices to prioritize long-term ecological health and social well-being over immediate gains.
6 | PNAS Nexus, 2024, Vol. 3, No. 4
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
implemented national policies alone, dangerous heating is only
avoidable with a massive rollout of GHG removal technologies and
large-scale ecosystem restoration that is nowhere in evidence today.
For instance, even the planned investment of $3.5B to develop four
“direct air capture” hubs under the 2022 US Bipartisan
Infrastructure Law will only remove the equivalent of 13 min of glo-
bal emissions at full annual capacity (30). Planting 8 billion trees, one
for every person on Earth, would remove the equivalent of only 43 h
of global emissions after the trees reached maturity decades from
now, and the change in albedo related to the new ground cover in-
creases the complexity of expected benets.
The only honest strategy for today is radical, immediate cuts in
fossil fuel use. Only after emissions have begun a rapid downward
trajectory should investments in carbon removal (the engineering
for which has yet to be dened or validated) occur with speed and
at scale (76). Even this will be met with ocean outgassing of CO
2
such that climate recovery will see a long delay (33).
This urgency is underscored by the fact that current emissions
are underreported, and decreasing natural carbon storage makes
limiting global temperatures even more challenging. Global emis-
sions are as much as 3 times higher than reported (77) with 70%
underreporting of energy-related CH
4
emissions alone (78). In
addition, the terrestrial biome, which sequesters about 31% of an-
thropogenic CO
2
emissions, has already neared, and in places
crossed, a photosynthetic thermal maximum beyond which ter-
restrial carbon storage will grow increasingly impossible (79).
For instance, global carbon loss from tropical forests has doubled
in the last 20 years (80), and the Brazilian portion of the Amazon
Forest has become a net GHG source (81). Eighty-three percent
of tropical forest carbon loss is driven by agriculture, suggesting
that strategies to reduce deforestation have failed, and that car-
bon emissions from forest destruction are undercounted (82).
The United Nations estimates that 1.84 billion people world-
wide, or nearly a quarter of humanity, were living under drought
in 2022 and 2023, the vast majority in low- and middle-income
countries (83). Megadrought projected for the year 2100 could
strike up to 50 years earlier according to models (84). Global heat-
ing risks food (85) and water (86) availability with human popula-
tions in conditions of extreme to exceptional drought (87)
doubling by 2100 (88).
Climate change threatens natural ecosystems (89), human se-
curity (90), livable conditions for communities (91), and the stabil-
ity of 1/3 of the human population (18). Under current levels of
heating, people are 15 times more likely to die from extreme wea-
ther than in years past, and 3.3 billion human lives are “highly vul-
nerable” to climate change (92). At 2°C heating, up to 3 billion
people may suffer chronic water scarcity. Today, 1 in 3 people
are exposed to deadly heat stress. This number is projected to in-
crease up to 75% by the end of the century.
By 2050, over 300 million people living on coasts will be exposed
to ooding from sea level rise (93). Forced to migrate, the impacts
of these displaced communities will ripple through the larger
population. Climate change drives the spread of disease in people,
crops, domesticated animals, and wildlife. Even if heating is held
below 1.6°C, 8% of today’s farmland will be unt to produce food.
Declining food production and nutrient losses will result in severe
stunting affecting 1 million children in Africa alone and cause 183
million additional people to go hungry by 2050 (92).
Abrupt change
Earth’s biophysical systems are shifting toward instability (94),
perhaps irreversibly (95). The IPCC has identied 15 Earth system
components with potential for abrupt destabilizing change, in-
cluding ice, ocean, and air circulation; large ecosystems; and pre-
cipitation. These systems are the pillars of life that permit stable
plant, animal, and microbial communities, food production, clean
water and establish the conditions for safe human development.
However, these systems may be characterized by threshold be-
havior. That is, they appear to remain stable as global tempera-
ture rises, but at a certain level of heating, they may “tip” into a
fundamentally irreversible new state (96).
As Earth retains heat, ice melt accelerates (97), especially in the
Arctic which is heating nearly 4 times faster than the global aver-
age (98). Arctic sea ice is declining (99), and the transition from a
snow- to rain-dominated Arctic in the summer and autumn
may occur as early as 2040, with profound climatic, ecosystem,
and socioeconomic impacts (100). The Greenland Ice Sheet is vul-
nerable to ice loss due to melt-elevation feedback (101), and
Greenland is losing ice 7 times faster than in the 1990s (102).
Antarctic melting has tripled in the past 5 years (103), and ice shelf
collapse may lead to amplied sea level rise (104, 105).
According to one study, if temperatures rise by 1.5°C, the loss of
four biophysical systems will become “likely” and loss of an add-
itional six will be “possible.” Loss of 13 biophysical systems will
be either “likely” or “possible” if the planet warms by 2.6°C, as ex-
pected under current climate policies (94). Emerging changes such
as deep ocean heating (106), marine stratication (107), declining
marine vertical circulation (108), and sea level rise (109) will con-
tinue for centuries even if net-zero emission targets are reached.
The Intergovernmental Panel on Climate Change Assessment
Report 6, Working Group I (110) projects possibly abrupt and irre-
versible change in permafrost carbon, West Antarctic ice sheets
and shelves, and ocean acidication and deoxygenation. These
changes could unleash feedback loops that place climate impacts
beyond our control (111).
Oceans
The world’s oceans face irreversible impacts from climate change,
with heating, acidication, stratication, and loss of dissolved
oxygen posing high costs for marine ecosystems (112). Ocean
heating has intensied (113), with the Southern Ocean taking up
most of the excess heat generated by anthropogenic activities
(114). These changes affect marine species distributions, interac-
tions, abundance, and biomass. Combined with other stressors
like pollution, they are putting marine biodiversity and its societal
benets at risk (115).
Amplied by global heating (116), marine biodiversity is being
decimated by more than 440,000 industrial shing vessels around
the world that are responsible for 72% of the world’s ocean catch.
Over 35% of the world’s marine shery stock is overshed and an-
other 57% is sustainably shed at the maximum level (117). One
study showed that more than 90% of the world’s marine food sup-
plies are at risk from environmental changes such as rising tem-
peratures and pollution, essential to over 3.2 billion people. Top
producers like China, Norway and the United States face the big-
gest threat (118). Marine heatwaves (119) are increasing with
negative impacts on marine organisms and ecosystems. Marine
coastal biodiversity is at risk, with over 98% of coral reefs pro-
jected to experience bleaching-level thermal stress by 2050 (120).
Relative to the period 1995–2014, global mean sea level is con-
servatively projected to rise 0.15–0.29 m by 2050, and 0.28–1.01 m
by 2100 (109). Higher rise would ensue from disintegration of
Antarctic ice shelves and faster-than-projected ice melt from
Greenland (121). On multiple occasions over the past 3 million
Fletcher et al. | 7
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
years, when temperatures increased 1–2°C, global sea levels rose
at least 6 m above present levels (122). Sea level rise will ood toxic
waste sites, cesspools and septic systems, municipal dumps, and
polluted groundwater. In many cases, communities of color will
be rst to experience health impacts (123).
Ocean pollution affects marine species and people who depend
on them. Toxic metals, plastics, manufactured chemicals, petrol-
eum, urban and industrial wastes, pesticides, fertilizers, pharma-
ceutical chemicals, agricultural runoff, and sewage are the most
detrimental and persistent pollutants (124). More than 80% of
marine pollutants originate from land-based sources, reaching
the oceans through rivers, runoff, and atmospheric deposition.
Pollution is heaviest in coastal waters, especially in low- and
middle-income countries (125).
Toxic metals such as mercury, lead, and cadmium accumulate
in marine animals, causing health problems in sh species and dis-
rupting endocrine systems in their human consumers (126). Plastics
take hundreds of years to degrade, breaking down into microplas-
tics that are ingested by sh, humans, and other organisms (127).
Manufactured chemicals such as polychlorinated biphenyls and di-
oxins are environmentally persistent toxins that accumulate in the
tissues of marine animals, disrupting hormonal systems (128).
Urban and agricultural runoff, and sewage contain pathogens
(129), heavy metals, and organic compounds that harm marine an-
imals and cause human health problems. Nitrogen pollution also
results in toxic algal blooms and oxygen-depleted dead zones
(130). The equity and justice implications of this massive problem
have been largely overlooked or downplayed (131).
Terrestrial biome
Tropical forests now emit more carbon than they are able to ab-
sorb from the atmosphere as a result of the dual effects of defor-
estation and land degradation (132). Rich-nation demand (133) for
lumber, minerals, beef, and animal feed outside their own borders
undermine attempts to mitigate climate change (134). Demand
for food, feed, ber, minerals, and energy is resulting in whole for-
ests being clear-cut. CO
2
emissions from boreal forest res have
reached a new high, producing nearly 1/4 of the total global CO
2
emissions from wildres (135). Only 40% of remaining forests
have high ecosystem integrity (136). Forests are degraded (137)
by drought, pests, and wildre related (138) to climate change.
Forest loss sacrices soil biodiversity and integrity to oxidation,
dehydration, and heating, transforming soil into a persistent
source of CO
2
emission (139). Only 2.9% of Earth’s land remains
ecologically intact (140). Essential ecosystems are disappearing,
and many species are at risk of extinction (141). Anthropogenic ex-
tinction rates are driving Earth’s sixth mass extinction (142). Each
year, the world consumes more than 92 Gt of materials—biomass
(mostly food), metals, fossil fuels, and minerals. This gure is
growing at the rate of 3.2% per year. Resources are being extracted
from the planet 3 times faster than in 1970, even though the popu-
lation has only doubled within that time (143). During the 20th
century, this boosted the global economy, but since then resour-
ces have become more expensive to extract and the environmen-
tal costs harder to ignore.
Both plant and soil carbon storage originate with photosynthesis,
which withdraws about 31% of annual anthropogenic CO
2
emis-
sions (2). However, studies (144) across a range of forest ecosystems
have found that heating leads to thermal stress and reduced carbon
assimilation. Many ecosystems (80) are already operating at or be-
yond thermal thresholds for photosynthesis (145). Widespread ter-
restrial ecological decline has resulted from the combination of
climate change, resource extraction, bushmeat hunting, and agri-
cultural and urban development. Since 1970, vertebrate popula-
tions have declined 69% (146), and 1 in 4 species are at risk of
extinction (147), in part because 75% of the terrestrial environment
has been severely altered by human actions.
Agricultural development has further eroded ecosystem
health, with over 15 billion trees per year lost since the emergence
of agriculture; the global number of trees has fallen by over 45%
(148). An estimated 67,340 km
2
of global forest were lost in 2021
alone, unleashing 3.8 Gt of GHG emissions, roughly 10% of the glo-
bal average (149). Such losses extend to wetland areas; more than
85% of the wetlands present in 1700 had been lost by 2000, and
loss of wetlands is currently 3 times faster than forest loss.
Food and water security
Increasing human population, and the need to expand food produc-
tion, were the drivers of the Green Revolution over 50 years ago
(150). This increased productivity through selective genetic breed-
ing, monocultures, seed improvement, and the use of chemical fer-
tilizers and pesticides. These steps have not solved the problem of
food insecurity which has been aggravated in more vulnerable pop-
ulations (151). Worldwide, it is estimated that 16,000 children are
pushed into hunger every day—a 32% increase from 2022 (152).
Agriculture now uses half of the world’s ice- and desert-free land,
and causes 78% of global ocean and freshwater eutrophication (153).
Pesticide and fertilizer runoff, as well as sewage, nd their way to
aquatic environments (154) and degrade water quality, while spread-
ing infectious diseases. Humans poison the soil annually with micro-
plastics between 4 and 23 times more than we do the oceans.
Microplastics reduce benecial bacteria concentrations, and can be
absorbed by plants, and then passed up the food chain (155).
Industrial farming employs deep plowing that depletes and ox-
idizes soil, turning acreage into a source of GHG (156). Agriculture
is responsible for 70% of global freshwater withdrawals (157). By
one estimate (158), 94% of nonhuman mammal biomass is now
livestock, and 71% of bird biomass is poultry livestock. 50% of all
agricultural expansion has come at the expense of forests. In
2022, the rate of global deforestation was the equivalent of 11 soc-
cer/football elds per minute (40), predominantly for cattle ranch-
ing and grain animal feed crops (such as soy) for export.
Today, agriculture uses half of all habitable land (159), and ei-
ther through grazing or growing animal feed, 77% of that is dedi-
cated to livestock (153). Animal agriculture is expanding. From
1998 to 2018 global meat consumption increased 58%. Cattle
and the grain they eat use 1/3 of all available land surface, 1/3
of global grain production, and 16% of all available freshwater.
Yet cattle agriculture only generates 18% of food calories and
27% of protein (153). The production of fertilizer for feed crops
emits 41 MtCO
2
/yr. The combination of emissions from manufac-
turing, transporting, and applying synthetic fertilizer on the land
(which releases the potent GHG N
2
O) today likely outpaces the
emissions of the commercial aviation industry. These fertilizer-
related GHG emissions are projected to grow. Additionally, live-
stock feed demands a minimum of 80% of global soybean crop
and over 50% of global corn crop. Thirty-ve to 40% of yearly an-
thropogenic CH
4
emissions are a result of domestic livestock pro-
duction due to enteric fermentation and manure (160).
Under a range of GHG emission pathways, cropland exposure
to drought and heat-wave events will increase by a factor of 10
in the midterm and a factor of 20–30 in the long term on all conti-
nents, especially Asia and Africa (161). Harvest failures across ma-
jor crop-producing regions are a threat to global food security. Jet
8 | PNAS Nexus, 2024, Vol. 3, No. 4
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
stream changes are projected to increase synchronous crop fail-
ure and lower crop yields in multiple agricultural regions around
the world (162). Crop failure due to drought, ood, or extreme
weather (163) events increases disproportionately between 1.5
and 2°C of global heating (164). For maize, risks of multiple bread-
basket failures increase from 6– 40% at 1.5°C to 54% at 2°C. In rela-
tive terms, the highest climate risk increases, between 1.5 and 2°C
heating, is for wheat (40%), followed by maize (35%) and soybean
(23%). Limiting global heating to 1.5°C would reduce the risk of
simultaneous crop failure for maize, wheat, and soybean by
26%, 28%, and 19%, respectively (164).
Demand for wheat is projected to increase 60% by 2050. Yet, ris-
ing CO
2
depletes the nutrient and protein content of wheat, and
with drought, re, and ood, leads to a 15% decline in projected
wheat yield by midcentury (165). Increased levels of CO
2
are de-
creasing the amount of protein, iron, zinc, and B vitamins in rice
with potential adverse health consequences for a global popula-
tion of approximately 600 million (166). Harvests of staple cereal
crops, such as rice and maize, could decrease by 20–40% as a func-
tion of heightened surface temperatures in tropical and subtrop-
ical regions by 2100 (167). This will exacerbate existing food
security issues, as 1 billion people are currently classied as
food insecure (168).
Worldwide, fungal infections cause growers to lose 10–23% of
their crops each year, and an additional 10–20% is lost following
harvest. Global heating is driving a poleward migration of fungal
infections, meaning more countries will see fungal infections
damaging harvests. Growers have reported wheat stem rust infec-
tions, usually tropical, in Ireland and England. Experts (169) also
warn that fungi tolerance to higher temperatures could increase
the likelihood of soil-dwelling pathogens to infect animals or hu-
mans. Across the ve most important calorie crops of rice, wheat,
maize (corn), soybeans, and potatoes, fungal infections already
cause losses equal to provisions for 600 million to 4 billion people.
Without major and rapid policy changes, food productivity in 2050
could be reduced to 1980 yield levels because new technologies
will be unable to mitigate climate change in major growing re-
gions (170).
Clean water security is a critical issue (171). Research shows
that groundwater levels are rapidly declining, especially in dry re-
gions with extensive croplands, and has accelerated over the past
four decades in 30% of the world’s regional aquifers (172). The
Southern Hemisphere has experienced a 20% drop in water avail-
ability over the past two decades (173). Approximately 3.6 billion
people, or 47% of the global population, suffer water scarcity at
least 1 month each year (174). Global water security is an urgent
concern due to the increasing imbalance between the nite supply
of freshwater and the escalating demand driven by population
growth, economic development, and agricultural needs. Climate
change compounds the crisis by altering precipitation patterns,
causing droughts, and depleting glaciers—key freshwater sour-
ces. Contamination from industrial, agricultural, and residential
waste further restricts the amount of clean water available. This
scarcity threatens human health, food production, and ecosystem
stability, leading to conicts and displacements. Addressing this
problem requires global cooperation for sustainable manage-
ment, technological innovation for conservation and purication,
and policies that prioritize equitable access to clean water (174).
Heat
The impact of heat on food production is disproportionately se-
vere in low-income communities. Workers in agriculture,
construction, and other outdoor sectors often work in conditions
that can lead to heat stress or heatstroke. Food production, too,
is critically affected as extreme heat can reduce crop yields, in-
crease irrigation needs, and lead to soil degradation. These com-
munities have less access to heat-protection technologies such
as air-conditioned spaces, efcient irrigation systems, or
heat-resistant crop varieties. Consequently, their economic sta-
bility and food security are more vulnerable to climate-induced
temperature increases, exacerbating existing inequalities and
pushing these populations further into poverty.
In 2022, global heat stress caused the loss of 490 billion poten-
tial labor hours, 143 h per person, a 42% increase from the 1991 to
2000 average (175). The loss of labor due to heat exposure resulted
in a $863 billion loss of “potential income” and wiped out the
equivalent of 4% of Africa’s GDP. The agriculture sector was hard-
est hit, accounting for 82% of losses in least developed countries.
The global land area affected by at least 1 month of extreme
drought per year increased from 18% averaged over the decade
1951–1960 to 47% in the decade 2013–2022. Because of heat stress,
under a 2°C warming scenario, 525 million additional people will
experience food insecurity by midcentury, compared to the period
1995–2014, and the number of heat-related deaths each year will
increase by 370%. Older people and infants now are exposed to
twice the number of heat-wave days annually as they were aver-
aged over the period 1986–2005.
Heat-related deaths of people older than 65 have increased by
85% since the 1990s (175). Even under moderate warming, heat
and drought levels in Europe that were virtually impossible 20
years ago reach 1-in-10 likelihoods as early as the 2030s (84).
Averaged over the period 2050–2074, projections for two succes-
sive years of single or compound end-of-century extremes, unpre-
cedented to date, exceed 1-in-10 likelihoods; while Europe-wide
5-year megadroughts become plausible. Whole decades of
end-of-century heat stress could start by 2040, by 2020 for
drought, and with a warm North Atlantic, end-of-century decades
starting as early as 2030 become twice as likely.
For thousands of years, fundamental limits on food and water
security meant that human communities have concentrated
under a narrow range of climate variables characterized by
mean annual temperatures (MATs) around 13°C (18). With contin-
ued GHG emissions, global heating of 3°C is projected to drive a
MAT >29°C across 19% of the planet’s land surface and displace
one-third of the human population. Today, this MAT accounts
for only 0.8% percent of Earth’s land surface, mostly concentrated
in the deep Sahara.
Model projections indicate that in the Middle East and North
Africa, continued emissions will cause the emergence of unprece-
dented super- and ultraextreme heat-wave conditions (176). These
events involve excessively warm temperatures (56°C and higher)
and will be of extended duration (several weeks), quickly becoming
life-threatening for humans (177). Researchers found that by 2100,
under current levels of GHG emissions, 3 of 4 people in the world
will be exposed to deadly heat conditions every year, with a higher
occurrence of these conditions in intertropical areas (2). Coupled
with signicant socioeconomic differences within countries, heat
waves intensify global disparities in health, especially given the de-
pleted resources for several of these regions to respond to acceler-
ated heating. In the last decade, there has been >2,300% increase
in the loss of human life from heat waves as a result of about 1°C
heating. On our current pathway, the global health and socio-
economic risks of continued heating are catastrophic.
The distribution of these conditions is unequal, and people and
communities subjected to the loss of security are powerless to
Fletcher et al. | 9
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
respond. The impacts of this inequity may cause regionally exist-
ential deterioration and suffering. As temperatures rise, death
rates increase most among the poorest populations (178). By
2099, under a scenario of continued high emissions growth, cli-
mate change increases death rates in low-income countries by
over 106 deaths per 100,000, while high-income countries are pro-
jected to see death rates decrease by 25 deaths per 100,000, while
spending signicantly to prevent more deaths. Overall, today’s
rich countries pay nearly 3 times more than poor countries to
adapt to rising temperatures and prevent additional deaths.
When it comes to cutting emissions, the social and economic bur-
den of inaction is predominantly carried by the poorest and most
vulnerable in human society, including Indigenous and local com-
munities, concentrated in developing countries.
Illness and disease
As the planet heats up, infectious diseases once conned to trop-
ical regions are expanding their range. The World Health
Organization estimates that by the end of this decade the climate
impact on health will cost between $2 billion and $4 billion per
year (179). Between 2030 and 2050, climate change is expected
to cause approximately 250,000 additional deaths per year from,
for example, undernutrition, malaria, cholera, diarrhea, and
heat stress alone. This does not include massive climate burdens
on agriculture, water, and sanitation, which also shape public
health.
In July 2023, for the rst time in 20 years, the United States ex-
perienced locally acquired malaria infections. Six cases were con-
rmed in Florida and one in Texas, none related to international
travel (180). In Seattle, cases of West Nile disease were reported
for the rst time. Over half of the infectious diseases confronted
by humanity have been aggravated by climatic hazards at some
point (181). All communities are vulnerable to climate change im-
pacts; however, children, elders, the sick, and the poor face the
greatest risks (182). People with cardiovascular and/or respiratory
chronic illnesses are particularly vulnerable to high temperatures
(183). Air pollution from GHG emissions leads to increased health
complications such as asthma and allergies. The impacts of cli-
mate change disproportionately affect vulnerable communities,
including low-income regions and communities of color which
have been disempowered by a history of colonialism, racism, op-
pression, and injustice. Extreme weather events further exacer-
bate the situation, driving animals and people together in
unsanitary conditions and disrupting essential services like
healthcare and clean water supplies.
Approximately 17% of diseases are spread by animal vectors
causing over 700,000 deaths annually. Concentrated animal farm-
ing operations are breeding grounds for virulent pathogens (184),
and over 15,000 new cases of mammals transmitting viruses to
other mammals could occur in the next 50 years due to climate
change (185). Smaller species like bats, rats, and other rodents
are thriving in human-populated areas, contributing to the spread
of diseases through their interactions. Biodiversity loss and
deforestation are directly linked to the rise of infectious diseases,
with 1/3 of zoonotic diseases attributed to these factors. Some 60%
of known pathogens, and 3 out of every 4 new or emergent infec-
tious diseases are zoonotic (186), and roughly 1/3 of those are at-
tributed to deforestation and habitat loss (187). A new disease
surfaces 5 times a year, and future global heating and precipita-
tion changes will further expand habitats for pathogens and vec-
tors, proliferating dengue fever, cholera, malaria, diarrhea, and
other diseases (188).
Climate change intensies the spread of infectious diseases,
particularly in low-income communities, by expanding the habi-
tats of disease vectors such as mosquitoes and ticks. Warmer tem-
peratures and altered rainfall patterns increase the incidence and
geographic range of vector-borne diseases like malaria and den-
gue fever. Flooding and extreme weather events, more common
as the climate changes, can lead to waterborne diseases due to
the contamination of freshwater supplies. Low-income areas
often have insufcient healthcare infrastructure, making them
more vulnerable to these outbreaks. Additionally, malnutrition
from climate-induced food scarcity can weaken immune systems,
further raising the susceptibility to infections. Thus, climate
change magnies health disparities, with low-income communi-
ties facing disproportionately high risks of disease.
Economic inequality, ecological destruction,
and global security
A grossly unequal distribution of wealth couples with the increas-
ing consumption patterns of a rising global middle class (189) to
amplify ecological destruction. The poorest half of the global
population owns barely 2% of total global wealth, while the richest
10% owns 76% of all wealth (190). The poorest 50% of the global
population contribute just 10% of emissions, while the richest
10% emit more than 50% total carbon emissions (191). Climate
change, economic inequality, and rising consumption levels inter-
twine to amplify ecological destruction.
Climate change, driven by carbon emissions, often stems from
industrial activities catering to increased consumption, particular-
ly in wealthier nations. This consumption depletes natural resour-
ces and exacerbates pollution and habitat loss. Economic
inequality compounds these issues, as poorer communities lack
the resources to adapt to environmental changes or invest in sus-
tainable practices. Consequently, low-income communities bear
the brunt of ecological degradation, such as soil erosion, water
scarcity, and biodiversity loss, while their limited economic means
prevent effective response or recovery. This cycle of consumption,
inequality, and environmental impact creates a feedback loop, per-
petuating and intensifying ecological damage globally.
Fifty years ago, underdevelopment and scarcity were drivers of
unsustainable resource use, but today these roots have morphed
into overdevelopment, afuence, and privilege driving unsustain-
able wealth accumulation and aggregate consumption. At pre-
sent, not a single country delivers what its citizens need without
transgressing planetary boundaries of long-term sustainability
(192). Modern imperialism amplies these inequalities through
economic exploitation, wealth accumulation, political interfer-
ence, cultural dominance, and other methods that leverage colo-
nial power structures. Recognizing and addressing neocolonial
practices is crucial for promoting equitable and sustainable devel-
opment and respecting the sovereignty and self-determination of
nations (193).
The use of natural materials and their benets are unevenly
distributed across the globe. Overconsumption is closely linked
to wealth and income disparities with large amounts of money
concentrated in a few rich countries, largely in the Northern
Hemisphere (194). For example, environmental stresses and
shocks related to natural resource extraction and use are out-
sourced to countries and regions outside the European Union,
while more than 85% of the economic benets stay within mem-
ber countries (195).
Global inequality results in fragile regions where intensied
conict over scarce resources allows malevolent actors to thrive
10 | PNAS Nexus, 2024, Vol. 3, No. 4
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
(196). One study (197) found strong causal evidence linking climat-
ic events to human conict across all major regions of the world:
for each 1 SD (1σ) change in climate toward warmer temperatures
or more extreme rainfall, data show that the frequency of inter-
personal violence rises 4% and the frequency of intergroup con-
ict rises 14%. Temperatures across the developed world are
expected to warm 2σ to 4σ by 2050. Hence, amplied rates of hu-
man conict could represent a large and critical impact of an-
thropogenic climate change.
Over the next 3 decades, even under best-case scenarios of low
heating, national, and global security face severe risks in every re-
gion of the world. Higher levels of heating will pose catastrophic,
and likely irreversible, global security risks over the course of the
21st century. A world where global mean surface temperature has
increased 3°C will be characterized by widespread and intense
heat stress, extreme weather events, ruptured and unproductive
marine and terrestrial ecosystems, broken food systems, disease
and morbidity, intense decadal megadrought, freshwater scarcity,
catastrophic sea level rise, and large numbers of migrant popula-
tions. By 2050, under these malignant conditions, up to 1.2 billion
humans could be displaced by climate change (198). These inten-
sifying crises now threaten the very fabric of our global socio-
economic system. Immediate action is imperative to avert a
collapse that endangers societal structures worldwide.
Climate purgatory
Although the global condition is bleak, after 200 years of fossil fuel
expansion, we are at a turning point in the energy system. The
clean-energy revolution is underway. Global sales of vehicles
powered by fossil fuels peaked in 2017 (199), and in 2023 electric
vehicle sales grew by 55%, reaching a record high of more than
10 million. For the rst time ever, announced manufacturing cap-
acity for electric vehicle batteries is now sufcient to fulll ex-
pected demand requirements by 2030 (200).
Renewable energy installations jumped nearly 50% in 2023, the
most rapid growth rate in two decades (200). After remaining at
for several years, global clean energy spending is increasing. Last
year, renewables made up about 30% of total electricity gener-
ation, up from 25% in 2018. Global investment in the energy tran-
sition totaled $1.77 trillion in 2023, an increase of 17% from the
prior year. Solar energy is expected to become the cheapest
form of energy in many places by 2030 and major global powers
are investing in infrastructure for energy transformation.
However, increasing global energy consumption offsets these
gains in renewable energy. Because of rising power needs in devel-
oping nations due to population growth and industrialization, on-
going electrication of the transport and building sectors, and
other areas of energy expansion, the International Energy
Agency (IEA) projects increasing growth of energy demand, rising
at an annual average rate of 3.4% in 2024–2026. Although the ex-
pansion of clean-energy sources is set to meet this demand
growth, decoupling energy consumption and CO
2
production,
the separation is not nearly wide enough to meet Paris
Agreement Goals for stopping global heating.
Countries and companies are taking steps to address climate
change while simultaneously making choices that undermine
these efforts. This paradox places us in a state of climate purga-
tory. The IEA predicts (200) a peak in fossil fuel demand by 2030,
but reports show governments planning to increase coal, oil,
and gas production well beyond climate commitments. This
math does not align with the 1.5°C or even the 2°C warming tar-
gets. Many experts consider these targets nearly impossible due
to the global reluctance to urgently phase out fossil fuels. In this
climate purgatory, we are at a critical juncture, where urgent,
transformative action is required to reconcile our ambitions
with our actions.
The 2023 UN “gap report” (26) tells us that governments plan to
produce around 110% more fossil fuels in 2030 than would be con-
sistent with limiting warming to 1.5°C, and 69% more than would
be consistent with 2°C. National carbon-cutting policies are so in-
adequate that 3°C of heating could be reached this century. Based
on existing national pledges, global emissions in 2030 will be only
2% below 2019 levels, rather than the 43% cut required to limit glo-
bal heating to 1.5°C. To get on track, 22 GtCO
2
must be cut from
currently projected global emissions in 2030. That is 42% of the to-
tal and equivalent to the output of the world’s ve worst polluters:
China, US, India, Russia, and Japan.
The world will need to increase climate spending to around $9
trillion annually by 2030 and to nearly $11 trillion by 2035 to roll
out clean sources of energy and prepare for the inevitable impacts
of a warming climate during coming decades (201). To limit warm-
ing to 1.5°C now requires eliminating emissions shortly after 2040.
Although technically feasible, few mainstream scientists believe
it is still achievable (202). Instead, analysts predict (203) that glo-
bal fossil fuel emissions will peak at some point in the next dec-
ade, followed not by a decline but a long plateau (204),
culminating with end-of-century warming potentially reaching
3°C (Fig. 4).
Although global renewable energy capacity is growing, there is
a lack of nancing for emerging and developing economies.
Redirecting nancial resources to lower income nations is crucial.
More than 90% of clean-energy investment comes from advanced
economies and China, risking new dividing lines in global energy.
The biggest shortfalls in clean-energy investment are in emerging
and developing economies. More needs to be done by the inter-
national community to drive investment in lower income econ-
omies, where the private sector has been reluctant to venture.
There is ample capital available—evidenced by the nearly $12 tril-
lion allocated for COVID-19 economic relief and the over $1 trillion
annually in fossil fuel subsidies, which balloons to $7 trillion with
indirect incentives. Reallocating these funds is complex, particu-
larly due to potential impacts on the poorest populations, yet it re-
mains a vital reservoir for investment as the world plans for a
sustainable future.
A new era of reciprocity with nature and
among human societies
The purpose of this review is to draw immediate attention to the
careless, foolish way that humanity is gambling with the future.
Unless things change dramatically, and soon, damage to the nat-
ural world will have long-lasting consequences for species and
ecosystems, and devastating upheavals for humanity. Although
this will particularly affect vulnerable populations, all of human-
ity faces an unprecedented catastrophe.
There are signs that humanity is awakening to the need for a
new system of values that recognize Earth as an island in space
with limitations on resource availability. No one is coming to res-
cue us. Many of the changes that we call for in this essay are con-
sistent with the work of the Intergovernmental Science-Policy
Platform on Biodiversity and Ecosystem Services (141) and the
UN SDG framework (205). But carbon assimilation in natural
systems is decreasing— potentially with signicant effects in
only decades; planetary-scale biophysical systems such as
the Atlantic Meridional Overturning Circulation, the Southern
Fletcher et al. | 11
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
Ocean overturning circulation, atmospheric Hadley circulation,
summer sea ice, tropical forests, and others have shifted and
are projected to falter. And urbanism, deforestation, consumer-
ism, pollution, disease, social stratication, and extractive agri-
culture are all on accelerating and expanding trends.
This is a human inection point that will determine future con-
ditions of life on Earth (206). While transitioning to a carbon-free
energy system comes with major societal restructuring, the socio-
economic adjustments needed to rapidly decrease emissions also
present opportunities for achieving social and ecological justice,
reducing disease, promoting the successful achievement of
SDGs, and securing food and water availablity for our children.
We can end pollution, improve human health, reign in popula-
tion growth, and reduce further biophysical risks. Indigenous com-
munities have practiced regenerative ways of managing natural
resources by understanding the reciprocal relationship between
humans and their natural surroundings. Nature is not a commodity
for exploitation, but a living system with its own rights, where hu-
mans are life-supported and in turn play a regenerative role. This
kinship promotes nature and humanity thriving together.
Under current national plans, global GHG emissions are set to
increase 9% by 2030, compared to 2010 levels. Yet the science is
clear: emissions must fall by 45% by the end of this decade com-
pared to 2010 levels to meet the goal of limiting global tempera-
ture rise to 1.5°C (207). As governments invest in renewable
energy sources, there are enormous cobenets to be gained in
terms of disease reduction, social equity, and a growing respect
for Earth’s rhythms. Yet renewable energy will not address the
root problem of ecological overshoot, social justice, or pollution.
Policies are needed that end the production of superuous and
luxury commodities, conserve energy at household and societal
levels, stabilize global population, and replace the extractive mod-
el with one that emphasizes true sustainability so that more nat-
ural resources per capita become available and wealth is far more
equitably distributed (208).
The shift away from an extractive, resource-driven global econ-
omy toward one that values human rights and livelihoods could
redene global economics and offer reasons for optimism.
Opportunities to prevent catastrophic levels of heating are being
missed due to accelerating consumerism, the false seduction of
dubious climate quick xes, unveriable “carbon offsets”, exorbi-
tant pollution levels, and growing economic disparity. Halting glo-
bal ecological decline and addressing the crises of climate change,
biodiversity collapse, pollution, pandemics, and human injustice
requires a shift in economic structures, human behavior, and
above all, values.
Whether the world is considered overpopulated depends on
various factors. It is essential to consider not only population
numbers but also consumption patterns, resource distribution,
and sustainability when discussing this complex issue.
Additionally, strategies for addressing concerns related to popula-
tion growth often involve a combination of policies related to edu-
cation, healthcare, resource management, and environmental
protection. In developing economies, overpopulation is not just
about how many people there are but also about how much
each person consumes compared to the availability of resources.
High levels of consumption in developed countries contribute
to environmental degradation, raising the issue of unequal distri-
bution of resources. While some regions may be densely popu-
lated and face resource constraints, others have much lower
population densities and abundant resources. Inequities in re-
source distribution can lead to perceptions of overpopulation
but are in reality more closely related to social inequalities, often
with deep historical roots related to imperialism and unjust re-
source extraction.
Humans must become rejuvenators of natural systems (209).
We must shift from wealth as a goal, to sustainaiblity as a goal
driving our decisons. This includes developing replacements for
plastics, adopting regenerative and restorative cultivation and
harvesting methods, investing in cradle to grave research and de-
velopment focused on material reuse, absolute decoupling of the
economy from net resource depletion, and establishing conserva-
tion goals to conserve 30–50% of Earth’s land, freshwater, and
oceans (210).
Fig. 4. Global GHG emissions and temperature rise. Net emissions including removals (billion metric tons of CO
2
-equivalent). Policy and technological
progress over the past 8 years has signicantly reduced the global temperature outlook. Models now project very likely temperature increases of 2.0 to
4.0°C by century’s end, with a 2.3 to 3.4°C likely range and a mean of 2.8°C. While this is progress from just 8 years ago, it still represents a dire climate
future—falling signicantly short of the Paris Agreement goal of limiting warming to well below 2°C (204).
12 | PNAS Nexus, 2024, Vol. 3, No. 4
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
Addressing social inequities based on gender, ethnicity, and in-
come is crucial, and leaders in political, educational, business,
and religious organizations must analyze and redress discrimin-
atory practices, historical racism, and unjust distributions of
power that hinder communities from adapting to climate change.
It is imperative to promote reproductive healthcare, education,
poverty eradication, ecological restoration, environmental just-
ice, and reciprocal relationships with nature. Economic develop-
ment must not come at the cost of destroying Earth.
As reported in numerous peer-reviewed studies (211), to re-
verse the many negative impacts generated by our modern socio-
economic system there must be global investment in (Fig. 5):
1. Rapid and legitimate decarbonization, correcting market distor-
tions favoring fossil fuels, avoiding the spurious trap of “net
zero” as an excuse to continue polluting the atmosphere
(212), and proper monitoring, verication, and reporting of
carbon offset contracts.
2. Revising the basis for decision-making under the UNFCCC.
Decision-making under the UNFCCC should be reorganized
by transitioning from unanimous voting to qualied majority
voting, enabling decisions to be made with agreement from a
dened majority of member nations. To encourage compli-
ance and accountability, penalties such as nancial sanctions
could be introduced for noncompliance with UNFCCC deci-
sions. These changes would enhance efciency, enabling
prompt action and stronger enforcement of climate-related
agreements among member nations.
3. Building a new era of reciprocity and kinship with nature, and de-
coupling economic activity from net resource depletion. We
must shift Earth-centered governance from an aspirational
political issue to a foundational principle through constitu-
tional reforms with policy implications (213).
4. Implementing sustainable/regenerative practices in all areas of
natural resource economics including, especially,
agriculture.
5. Eliminating environmentally harmful subsidies and restricting trade
that promotes pollution and unsustainable consumption.
6. Promote gender justice by supporting women’s and girls’ educa-
tion and rights, which reduces fertility rates and raises the
standard of living.
7. Accelerating human development in all SDG sectors, especially
promoting reproductive healthcare, education, and equity
for girls and women.
8. In low- and middle-income nations, relieving debt, providing low-
cost loans, nancing loss and damage, funding clean-energy
acceleration, arresting the dangerous loss of biodiversity,
and restoring natural ecosystems.
A cultural shift in values
How do we achieve these goals? The authors call for a global cul-
tural shift in social and economic values. Creating a cultural shift
toward regenerative practices in socioeconomic activities is com-
plex and requires a multifaceted approach involving, critically,
the leaders of the G20, and all nations, comprehensively engaging
programs in the following:
1. Education in sustainability and equity concepts: Increasing
awareness and understanding of sustainability and equity
issues through education at all levels to empower individu-
als to make more environmentally conscious decisions.
Embedding sustainability and equity into educational
curricula at all levels can shape future generations’ values
and actions. We advocate adoption of the issues discussed
in this paper in school curricula, public service announce-
ments, and as a guide to government decision-making.
2. Policy, legal frameworks, and legislation: Governments can en-
act and enforce policies that mandate sustainable practices
and ensure social equity, such as progressive environmental
regulations, social justice legislation, and economic reforms
that prioritize community well-being over individual prot.
3. Economic incentives: Shifting the economic focus from growth
at any cost to a model that values environmental and social
well-being. Aligning economic incentives with sustainable
outcomes, such as tax breaks for green businesses, can en-
courage companies and consumers to adopt better
practices.
4. Cross-sector partnerships: Facilitating collaboration between
the public sector, private sector, civil society, and academia
to develop integrated and comprehensive approaches to
sustainability and equity.
5. Community empowerment and inclusion: Encouraging partici-
patory governance that includes diverse community voices
in decision-making processes, particularly those of margi-
nalized and indigenous groups, to ensure that practices
are equitable and culturally sensitive.
6. Corporate responsibility and accountability: Promoting corpor-
ate social responsibility through transparency, fair trade,
ethical sourcing, and sustainability reporting.
7. Incentives for sustainable/equitable behavior: Channeling in-
vestment into the development and deployment of green
technologies that enable sustainable production and con-
sumption patterns. Creating economic and social incentives
for businesses and individuals to adopt sustainable practi-
ces, like subsidies for renewable energy or tax benets for
sustainable/equitable business practices.
8. Innovation and technology: Investing in research and develop-
ment for new technologies can provide more efcient and
cleaner alternatives to current practices.
9. Leadership and commitment: Encouraging leaders within com-
munities, businesses, and governments to model sustain-
able and equitable behaviors. Leaders in business, politics,
and community groups must commit to sustainability goals
and lead by example to inspire others.
10. Cultural narratives: Leveraging media, art, and culture to pro-
mote stories and images that valorize sustainability and
equity, thereby shaping public opinion and cultural values.
Changing the cultural narratives around consumption and
progress to value sustainability and long-term thinking
over immediate gratication or economic growth at any
cost.
11. Global engagement and solidarity: Participating in international
efforts and agreements that aim to address global chal-
lenges collectively, ensuring that sustainability and social
equity are global priorities.
This systemic transformation requires a shift in collective values,
behaviors, and institutional practices to prioritize long-term eco-
logical health and social well-being over immediate gains.
Heads of state must immediately pivot the considerable power of
the economy toward restoring a livable planet and an equitable and
just socioeconomic system. To achieve a successful future where hu-
manity can thrive, economic values must embrace human equity,
health, and welfare, kinship with nature, regenerative resource
Fletcher et al. | 13
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
use, sustainability, and resilience. Emphasizing fairness and inclu-
sivity, these values promote social cohesion and reduce disparities.
Recognizing our interconnectedness with the environment, a fo-
cus on sustainability and regenerative resource use ensures the pres-
ervation of nature for future generations. Prioritizing health and
well-being, societies must invest in healthcare systems, fostering a
higher quality of life by building resilience against uncertainties. A
new economic paradigm is needed to create a prosperous and harmo-
nious future, meeting the challenges of a rapidly deteriorating world.
Earth is our lifeboat in the sea of space
As succinctly stated by Rees (68), “We are consuming and pollut-
ing the biophysical basis of our own existence.” Climate change,
biodiversity loss, pollution, disease, and social injustice risk the
stability of human communities on Earth (Fig. 6). We must stop
treating these issues as isolated challenges, and establish a sys-
temic response based on kinship with nature that recognizes
Earth as our lifeboat in the cosmic sea of space.
Fig. 5. The historical context of imperialism, population growth, and an extractive relationship with nature has led to a series of modern outcomes that
put our planet at risk: disease, climate change, biodiversity loss, socioeconomic inequality, and pollution. These risk the stability of human communities.
Humanity may achieve a just and sustainable future through global investment in rapid decarbonization, correcting market distortions favoring fossil
fuels, avoiding “net zero” as an excuse to continue GHG emissions, proper monitoring and validation of carbon offsets, revising the basis for
decision-making under the UNFCCC, decoupling economic activity from net resource depletion, shifting to Earth-centered governance, sustainable/
regenerative practices in all areas of natural resource economics, eliminating environmentally harmful subsidies, restrict trade that promotes pollution
and unsustainable consumption, accelerate human development in all SDG sectors, promote gender justice by supporting women’s and girls’ education
and rights which reduces fertility rates and raises the standard of living, and for low- and middle-income nations: relieve debt, provide low-cost loans,
nance loss and damage, fund clean-energy acceleration, arrest the dangerous loss of biodiversity, and restore natural ecosystems.
14 | PNAS Nexus, 2024, Vol. 3, No. 4
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
Coauthor Jay Bowen, Upper Skagit Elder, explained why North
American Indigenous Peoples described their North America as
“turtle island” (Fig. 6):
“It was not understood why the ancestors had referenced it in this
way until the pictures of Earth were seen in 1969 from the Apollo
Space Mission. The outline of North America resembled a turtle.
We had an understanding of the whole Earth even though we lived
on only a tiny piece of it. The ancestors understood global society.
We understood that Earth was of one family. This family built and
strengthened ties through voyaging to engage in trade, cultural ex-
change, and discovery.”
There is no guarantee of a just, nourishing, and healthy future
for humanity, and hope will not catalyze the change we need.
That work must fall upon us, and it is clear from this review
that we are past due for, and critically far away from, an appropri-
ate reaction to the global emergency we have created.
Note
a
“Ecological overshoot” is dened as depleting essential ecosystems
faster than they can regenerate and polluting the ecosphere beyond
nature’s assimilative capacity.
Acknowledgments
This work was supported in part by the University of Hawai‘i at
Ma
noa, School of Ocean and Earth Science and Technology. Many
thanks to artists Brooks Bays, Nancy Hulbirt, and Georgina Casey.
Funding
Costs related to illustration and public access provided by the
School of Ocean and Earth Science and Technology, University
of Hawai‘i at Ma
noa, Honolulu, HI, US.
Author Contributions
C.F. conceived this work and wrote the original draft. W.J.R., T.N.,
P.B., E.C., C.F., D.M.K., A.B., and K.H. provided substantial edits.
K.B., J.B., M.C., C.F., D.A.K., M.E.M., D.P.M., C.M., N.O., and M.W. re-
viewed and edited drafts of the manuscript.
References
1 IPCC. 2023. Summary for policymakers. In: Climate change 2023: syn-
thesis report. Contribution of Working Groups I, II, and III to the Sixth
Assessment Report of the Intergovernmental Panel on Climate Change.
Geneva: IPCC. p. 1–34.
2 Friedlingstein P, et al. 2023. Global carbon budget 2023. Earth
Syst Sci Data. 15:5301–5369.
3 World Meteorological Organization. WMO confirms that 2023
smashes global temperature record. WMO [2024 Jan 12].
https://wmo.int/media/news/wmo-confirms-2023-smashes-
global-temperature-record.
4 Mora C, et al. 2017. Global risk of deadly heat. Nat Clim Change. 7:
501–506.
5 Abatzoglou JT, Williams AP. 2016. Impact of anthropogenic cli-
mate change on wildfire across western US forests. Proc Natl
Acad Sci U S A. 113:11770–11775.
6 Williams AP, Cook BI, Smerdon JE. 2022. Rapid intensification of
the emerging Southwestern North American megadrought in
2020–2021. Nat Clim Change. 12:232–234.
7 World Meteorological Organization. The global climate 2011–
2020: a decade of acceleration. WMO [accessed 2023 Dec 5].
https://wmo.int/resources/publications/global-climate-2011-
2020-decade-of-acceleration.
8 Wiens JJ. 2016. Climate-related local extinctions are already
widespread among plant and animal species. PLoS Biol. 14:
e2001104.
9 Exposito-Alonso M, et al. 2022. Genetic diversity loss in the
Anthropocene. Science. 377:1431–1435.
10 Díaz S, et al. 2019. Pervasive human-driven decline of life on
earth points to the need for transformative change. Science.
366:eaax3100.
11 Ripple WJ, et al. 2017. World scientists’ warning to humanity: a
second notice. BioScience. 67:1026–1028.
12 IPCC. 2021. Climate change 2021: the physical science basis.
Contribution of Working Group I to the Sixth Assessment Report of
the Intergovernmental Panel on Climate Change. Cambridge (UK)
and New York (NY): Cambridge University Press. p. 2391.
13 International Energy Agency. Oil 2023: analysis and forecast to
2028. IEA [accessed 2023 Jun]. https://www.iea.org/reports/oil-2023.
14 UN Framework Convention on Climate Change. Addendum to
the synthesis report for the technical assessment component
of the first global stocktake. UNCC [accessed 2023 Apr 17].
https://unfccc.int/documents/627853.
15 Perkins R, Edwardes-Evans H. Fossil fuels ‘stubbornly’ dominat-
ing global energy despite surge in renewables: energy institute.
S&P Global Commodity Insights [accessed 2023 Jun 26]. https://
www.spglobal.com/commodityinsights/en/market-insights/
latest-news/oil/062623-fossil-fuels-stubbornly-dominating-
global-energy-despite-surge-in-renewables-energy-institute.
Fig. 6. Turtle Island. Original art commissioned for this paper, Jay Bowen
(https://jaybowen-art.com/wordpress/).
Fletcher et al. | 15
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
16 Samset BH,et al. 2023. Steady global surface warming from 1973
to 2022 but increased warming rate after 1990, https://doi.org/
10.1038/s43247-023-01061-4. Commun Earth Environ. 4:400.
17 Hansen JE, et al. 2023. Global warming in the pipeline. Oxf Open
Clim Change. 3:kgad008.
18 Xu C, Kohler TA, Lenton TM, Svenning J-C, Scheffer M. 2020.
Future of the human climate niche. Proc Natl Acad Sci U S A.
117:11350–11355.
19 Lenton TM, et al. 2023. Quantifying the human cost of global
warming. Nat Sustain. 6:1237–1247.
20 Thiery W, et al. 2021. Intergenerational inequities in exposure to
climate extremes. Science. 374:158–160.
21 Wiens JJ, Zelinka J. 2024. How many species will earth lose to cli-
mate change? Glob Change Biol. 30:e17125.
22 Park BY, et al. 2021. The association between wildfire exposure
in pregnancy and foetal gastroschisis: a population-based co-
hort study. Paediatr Perinat Epidemiol. 36:45–53.
23 Mann ME, et al. 2017. Influence of anthropogenic climate
change on planetary wave resonance and extreme weather
events. Sci Rep. 7:45242.
24 Mann ME, et al. 2018. Projected changes in persistent extreme
summer weather events: the role of quasi-resonant amplifica-
tion. Sci Adv. 4:eaat3272.
25 Climate Action Tracker. The CAT thermometer. Climate Action
Tracker [accessed 2023 Dec]. https://climateactiontracker.org/
global/cat-thermometer/.
26 United Nations Environment Programme. 2023. Emissions gap re-
port 2023: broken record—temperatures hit new highs, yet world fails
to cut emissions (again). Nairobi: United Nations Environment
Programme.
27 Lamboll RD, et al. 2023. Assessing the size and uncertainty of re-
maining carbon budgets. Nat Clim Change. 13:1360–1367.
28 SEI, Climate Analytics, E3G, IISD, UNEP. 2023. The production
gap report 2023: Phasing down or phasing up? Top fossil fuel
producers plan even more extraction despite climate promises.
SEI. https://doi.org/10.51414/sei2023.050.
29 Barbier EB. 2023. Three climate policies that the G7 must adopt
—for itself and the wider world. Nature. 617:459–461.
30 Ho DT. 2023. Carbon dioxide removal is not a current climate
solution—we need to change the narrative. Nature. 616:9.
31 Dyke J, Watson R, Knorr W. Climate scientists: concept of net
zero is a dangerous trap. The Conversation [2021 Apr 22].
https://theconversation.com/climate-scientists-concept-of-net-
zero-is-a-dangerous-trap-157368.
32 Kapla RS, Ramanna K, Roston M. Accounting for carbon offsets.
Harvard Business Review [accessed 2024 Mar 16]. https://hbr.
org/2023/07/accountingfor-carbon-offsets.
33 Kim S-Y, et al. 2023. Hemispherically asymmetric Hadley cell re-
sponse to CO
2
removal. Sci Adv. 9:eadg1801.
34 Shuen R. 2021. Addressing a constitutional right to a safe cli-
mate: using the court system to secure climate justice. J Gend
Race Justice. 24:377–410.
35 United Nations Environment Programme. 2023. Global climate
litigation report: 2023 status review. Nairobi: United Nations
Environment Programme.
36 Dolšak N, Prakash A. 2022. Three faces of climate justice. Annu
Rev Political Sci. 25:283–301.
37 Pearson Z, Ellingrod S, Billo E, McSweeney K. 2019. Corporate so-
cial responsibility and the reproduction of (neo)colonialism in
the Ecuadorian Amazon. Extr Ind Soc. 6:881–888.
38 Dunlap A. 2021. The politics of ecocide, genocide and megapro-
jects: interrogating natural resource extraction, identity and
the normalization of erasure. J Genocide Res. 23:212–235.
https://doi.org/10.1080/14623528.2020.1754051.
39 Lenin VI. 2017. Imperialism, the highest stage of capitalism. In:
Betts RK, editor. Conflict after the Cold War. 5th ed. New York:
Routledge. p. 319–326.
40 Weisse M, Goldman E, Carter S. Tropical primary forest loss
worsened in 2022 despite international commitments to end
deforestation. Global Forest Review. World Resources
Institute [accessed 2024 Mar 16]. https://research.wri.org/gfr/
latest-analysis-deforestation-trends?utm_campaign=treecover
loss2022&utm_medium=bitly&utm_source=PressKit.
41 Bradshaw CJ, et al. 2021. Underestimating the challenges of
avoiding a ghastly future. Front Conserv Sci. 1:9.
42 United Nations. Global issues: population. UN [accessed 2024
Mar 16]. https://www.un.org/en/global-issues/population#
:%E2%88%BC:text=The%20world’s%20population%20is%
20expected,billion%20in%20the%20mid%2D2080s.
43 Dasgupta P. 2019. Time and the generations: population ethics for a
diminishing planet. New York: Columbia University Press.
44 PWC. The long view, how will the global economic order change
by 2050? PWC [accessed 2024 Mar 16]. https://www.pwc.com/
gx/en/world-2050/assets/pwc-the-world-in-2050-full-report-
feb-2017.pdf.
45 Rees WE. 2023. The human ecology of overshoot: why a major
‘population correction’ is inevitable. World. 4:509–527.
46 Speidel JJ, O’Sullivan JN. 2023. Advancing the welfare of people
and the planet with a common agenda for reproductive justice,
population, and the environment. World. 4:259–287.
47 Willcock S, Cooper GS, Addy J, Dearing JA. 2023. Earlier collapse
of Anthropocene ecosystems driven by multiple faster and
noisier drivers. Nat Sustain. 6:1331–1342.
48 United Nations. Global sustainable development report (GSDR)
2023. Advance, unedited version. UN [accessed 2024 Mar 16).
https://sdgs.un.org/gsdr/gsdr2023.
49 Wunderling N, et al. 2022. Global warming overshoots increase
risks of climate tipping cascades in a network model. Nat Clim
Change. 13:75–82.
50 Dasgupta P, Levin S. 2023. Economic factors underlying bio-
diversity loss. Philos Trans R Soc B Biol Sci. 378:20220197.
51 Garcia AC, Ambrose A, Hawkins A, Parkes S. 2021. High con-
sumption, an unsustainable habit that needs more attention.
Energy Res Soc Sci. 80:102241.
52 Lampert A. 2019. Over-exploitation of natural resources is fol-
lowed by inevitable declines in economic growth and discount
rate. Nat Commun. 10:1419.
53 Brooks DR, Hoberg EP, Boeger WA, Trivellone V. 2022. Emerging
infectious disease: an underappreciated area of strategic con-
cern for food security. Transbound Emerg Dis. 69:254–267.
54 Hannah DM, et al. 2022. Illuminating the ‘invisible water crisis’
to address global water pollution challenges. Hydrol Process. 36:
e14525.
55 Rivera A, Darden JT, Dear N, Grady SC. 2023. Environmental in-
justice among hispanics in Santa Clara, California: a human–
environment heat vulnerability assessment. GeoJournal. 88:
2651–2667.
56 Atwoli L, et al. 2021. Call for emergency action to limit global
temperature increases, restore biodiversity, and protect health.
Lancet. 398:939–941.
57 Blattner C. 2020. Just transition for agriculture? A critical step in
tackling climate change. J Agric Food Syst Community Dev. 9:
53–58.
16 | PNAS Nexus, 2024, Vol. 3, No. 4
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
58 Bordner AS, Ferguson CE, Ortolano L. 2020. Colonial dynamics
limit climate adaptation in Oceania: perspectives from the
Marshall Islands. Glob Environ Change. 61:102054.
59 Climate Central. Worldwide daily fingerprints of climate
Change during earth’s hottest month. Climate Central [ac-
cessed 2023 Aug 2]. https://www.climatecentral.org/climate-
matters/climate-shift-index-global-july-2023.
60 Hansen J, Sato M, Kharecha P. Groundhog Day. Another
Gobsmackingly bananas month. What’s up? [accessed 2024 Mar
16]. https://www.columbia.edu/~jeh1/mailings/2024/Groundhog.
04January2024.pdf.
61 Zachariah M, et al. Extreme heat in North America, Europe and
China in July 2023 made much more likely by climate change.
Imperial College [accessed 2024 Mar 16]. https://spiral.
imperial.ac.uk/handle/10044/1/105549.
62 Sze JS, Childs DZ, Carrasco LR, Edwards DP. 2022. Indigenous
lands in protected areas have high forest integrity across the
tropics. Curr Biol. 32:4949–4956.e3.
63 Gonçalves CD, Schlindwein MM, Martinelli GD. 2021.
Agroforestry systems: a systematic review focusing on trad-
itional indigenous practices, food and nutrition security, eco-
nomic viability, and the role of women. Sustainability. 13:11397.
64 Epstein Y, Ellison AM, Echeverría H, Abbott JK. 2023. Science
and the legal rights of nature. Science. 380:eadf4155.
65 Koplow D, Steenblik R. Protecting nature by reforming environ-
mentally harmful subsidies: the role of business [accessed 2022
Feb]. https://www.earthtrack.net/sites/default/files/documents/
EHS_Reform_Background_Report_fin.pdf.
66 Hickel J, Kallis G. 2019. Is green growth possible? New Political
Econ. 25:469–486.
67 Briel G. Economic growth and the environment–is green growth
possible? Tralac [accessed 2022 Apr 21]. https://www.tralac.
org/blog/article/15589-economic-growth-and-the-environment-
is-green-growth-possible.html#_ftn9.
68 Rees WE. 2023. The human eco-predicament: overshoot and the
population conundrum. Vienna Yearb Popul Res. 21:1–19.
69 NOAA Global Monitoring Laboratory. Trends in atmospheric
carbon dioxide. NOAA [accessed 2024 Mar 16]. https://gml.
noaa.gov/ccgg/trends/.
70 Ciais P, et al. 2013. Carbon and other biogeochemical cycles. In:
Stocker TF, et al., editors. Climate change 2013: the physical science
basis. Contribution of Working Group I to the Fifth Assessment Report
of the Intergovernmental Panel on Climate Change. Cambridge (UK):
Cambridge University Press. p. 6SM-1–4.
71 Dumitru OA, et al. 2019. Constraints on global mean sea level
during Pliocene warmth. Nature. 574:233–236.
72 Lan X, et al. 2021. Improved constraints on global methane
emissions and sinks using δ
13
C-CH
4
. Glob Biogeochem Cycles. 35:
e2021GB007000.
73 IPCC. 2021. Summary for policymakers. Climate change 2021: the
physical science basis. Cambridge (UK): Cambridge University
Press.
74 Climate Action Tracker. 2030 emissions gap: CAT projections
and resulting emissions gap in meeting the 1.5°C Paris agree-
ment goal. Climate Action Tracker [accessed 2023 Dec 5].
https://climateactiontracker.org/global/cat-emissions-gaps/.
75 Kalmus P. 2023 Jul 27. Joe Biden must declare a climate emer-
gency. And he must do so now. The Guardian. https://www.
theguardian.com/commentisfree/2023/jul/27/joe-biden-climate-
emergency-peter-kalmus.
76 Climate Crisis Advisory Group (CCAG). A critical pathway for a
manageable future for humanity. CCAG [accessed 2024 Mar 16].
https://www.ccag.earth/.
77 Harvey F. 2022 Nov 9. Oil and gas greenhouse emissions ‘three
times higher’ than producers claim. The Guardian. https://
www.theguardian.com/environment/2022/nov/09/oil-and-gas-
greenhouse-emissions-three-times-higher-than-producers-
claim.
78 International Energy Agency. Methane emissions from the en-
ergy sector are 70% higher than official figures. IEA [accessed
2022 Feb 23]. https://www.iea.org/news/methane-emissions-
from-the-energy-sector-are-70-higher-than-official-figures.
79 Duffy KA, et al. 2021. How close are we to the temperature tip-
ping point of the terrestrial biosphere? Sci Adv. 7:eaay1052.
80 Feng Y, et al. 2022. Doubling of annual forest carbon loss over
the tropics during the early twenty-first century. Nat Sustain.
5:444–451.
81 Gatti LV, et al. 2021. Amazonia as a carbon source linked to de-
forestation and climate change. Nature. 595:388–393.
82 Li Y, et al. 2022. Deforestation-induced climate change reduces
carbon storage in remaining tropical forests. Nat Commun. 13:
1964.
83 United Nations Convention to Combat Desertification. Global
drought snapshot. UNCCD [accessed 2024 Mar 16]. https://www.
droughtglobal.org/_files/ugd/184219_4dcb7a4451514f2281981f60
4c3848cc.pdf?index=true.
84 Suarez-Gutierrez L, Müller WA, Marotzke J. 2023. Extreme heat
and drought typical of an end-of-century climate could occur
over Europe soon and repeatedly. Commun Earth Environ. 4:415.
85 Teressa B. 2021. Impact of climate change on food availability—
a review. Int J Food Sci Agric. 5:465–470.
86 Vollmer D, Harrison IJ. 2021. H
2
O≠CO
2
: framing and responding
to the global water crisis. Environ Res Lett. 16:011005.
87 Chiang F, Mazdiyasni O, AghaKouchak A. 2021. Evidence of an-
thropogenic impacts on global drought frequency, duration,
and intensity. Nat Commun. 12:2754.
88 Pokhrel Y, et al. 2021. Global terrestrial water storage and
drought severity under climate change. Nat Clim Change. 11:
226–233.
89 Nolan C, et al. 2018. Past and future global transformation of ter-
restrial ecosystems under climate change. Science. 361:920–923.
90 Brock S, et al. 2021. The world climate and security report 2021: a
product of the expert group of the International Military Council on
Climate and Security. Washington (DC): Center for Climate and
Security.
91 Clement V, et al. 2021. Groundswell part 2: acting on internal climate
migration. Washington (DC): World Bank.
92 IPCC. 2022. Climate change 2022: impacts, adaptation and vul-
nerability. In: Pörtner HO, et al., editors. Climate change 2022: im-
pacts, adaptation and vulnerability. Contribution of Working Group II
to the Sixth Assessment Report of the Intergovernmental Panel on
Climate Change. Cambridge (UK): Cambridge University Press.
p. 3–33.
93 Kulp SA, Strauss BH. 2019. New elevation data triple estimates
of global vulnerability to sea-level rise and coastal flooding. Nat
Commun. 10:4844.
94 Lenton TM, et al. 2019. Climate tipping points—too risky to bet
against. Nature. 575:592–595.
95 McKay DIA, et al. 2022. Exceeding 1.5°C global warming could
trigger multiple climate tipping points. Science. 377:eabn7950.
96 Ripple WJ, et al. 2023. Many risky feedback loops amplify the
need for climate action. One Earth. 6:86–91.
97 Slater T, et al. 2021. Earth’s ice imbalance. Cryosphere. 15:
233–246.
Fletcher et al. | 17
Downloaded from https://academic.oup.com/pnasnexus/article/3/4/pgae106/7638480 by guest on 05 April 2024
98 Rantanen M, et al. 2022. The Arctic has warmed nearly four
times faster than the globe since 1979. Commun Earth Environ.
3:168.
99 Perovich D, et al. 2019. Sea ice. In: Richter-Menge J,
Druckenmiller M, Jeffries M, editors. Arctic report card 2019.
Silver Spring (MD): NOAA. p. 26–34.
100 McCrystall MR, Stroeve J, Serreze M, Forbes BC, Screen JA. 2021.
New climate models reveal faster and larger increases in Arctic
precipitation than previously projected. Nat Commun. 12:6765.
101 Höning D, et al. 2023. Multistability and transient response of
the Greenland ice sheet to anthropogenic CO
2
emissions.
Geophys Res Lett. 50:e2022GL101827.
102 The IMBIE Team. 2020. Mass balance of the Greenland ice sheet
from 1992 to 2018. Nature. 579:233–239.
103 The IMBIE Team. 2018. Mass balance of the Antarctic ice sheet
from 1992 to 2017. Nature. 558:219–222.
104 Rignot E, Mouginot J, Morlighem M, Seroussi H, Scheuchl B.
2014. Widespread, rapid grounding line retreat of Pine Island,
Thwaites, Smith, and Kohler glaciers, West Antarctica, from
1992 to 2011. Geophys Res Lett. 41:3502–3509.
105 Joughin I, Smith BE, Medley B. 2014. Marine ice sheet collapse
potentially under way for the Thwaites glacier basin, West
Antarctica. Science. 344:735–738.
106 Messias M-J, Mercier H. 2022. The redistribution of anthropo-
genic excess heat is a key driver of warming in the North
Atlantic. Commun Earth Environ. 3:118.
107 Li G, et al. 2020. Increasing ocean stratification over the past
half-century. Nat Clim Change. 10:1116–1123.
108 Li Q, England MH, Hogg AM, Rintoul SR, Morrison AK. 2023.
Abyssal ocean overturning slowdown and warming driven by
Antarctic meltwater. Nature. 615:841–847.
109 Fox-Kemper B, et al. 2021. Ocean, cryosphere and sea level
change. In: Masson-Delmotte V, et al., editors. Climate change
2021: the physical science basis. Cambridge (UK): Cambridge
University Press. p. 1211–1362.
110 Lee JY, et al. 2021. Future global climate: scenario-based projec-
tions and near-term information. In: Masson-Delmotte V, et al.,
editors. Climate change 2021: the physical science Basis. Cambridge
(UK): Cambridge University Press. p. 1–195.
111 Hansen J, et al. 2016. Ice melt, sea level rise and superstorms:
evidence from paleoclimate data, climate modeling, and mod-
ern observations that 2°C global warming could be dangerous.
Atmos Chem Phys. 16:3761–3812.
112 Heinze C, et al. 2020. The quiet crossing of ocean tipping points.
Proc Natl Acad Sci U S A. 118:e2008478118.
113 Von Schuckmann K, et al. 2020. Heat stored in the earth system:
where does the energy go? Earth Syst Sci Data. 12:2013–2041.
114 Cheng L, et al. 2024. New record ocean temperatures and related
climate indicators in 2023. Adv Atmos Sci. 1–15
115 Penn JL, Deutsch C. 2022. Avoiding ocean mass extinction from
climate warming. Science. 376:524–526.
116 Pauly D. 2019. Vanishing fish: shifting baselines and the future of glo-
bal fisheries. Vancouver (CA): Greystone Books.
117 FAO. The state of world fisheries and aquaculture 2022.
Towards blue transformation. FAO [accessed 2024 Mar 16].
https://doi.org/10.4060/cc0461en.
118 Cao L, et al. 2023. Vulnerability of blue foods to human-induced
environmental change. Nat Sustain. 6:1186–1198.
119 Cheng Y, et al. 2023. A quantitative analysis of marine heat-
waves in response to rising sea surface temperature. Sci Total
Environ. 881:163396.
120 Heron SF, Maynard JA, Van Hooidonk R, Eakin CM. 2016.
Warming trends and bleaching stress of the world’s coral reefs
1985–2012. Sci Rep. 6:38402.
121 Ciracì E, et al. 2023. Melt rates in the kilometer-size grounding
zone of Petermann Glacier, Greenland, before and during a re-
treat. Proc Natl Acad Sci U S A. 120:e2220924120.
122 Dutton A, et al. 2015. Sea-level rise due to polar ice-sheet mass
loss during past warm periods. Science. 349:aaa4019.
123 Cushing LJ, et al. 2023. Toxic tides and environmental injustice:
social vulnerability to sea level rise and flooding of hazardous
sites in coastal California. Environ Sci Technol. 57:7370–7381.
124 Landrigan PJ, et al. 2020. Human health and ocean pollution.
Ann Glob Health. 86:151.
125 Bennett NJ, et al. 2023. Environmental (in)justice in the
Anthropocene ocean. Mar Policy. 147:105383.
126 Mahjoub M, Fadlaoui S, El Maadoudi M, Smiri Y. 2021. Mercury,
lead, and cadmium in the muscles of five fish species from the
Mechraâ-Hammadi Dam in Morocco and health risks for their
consumers. J Toxicol. 2021:8865869.
127 Thushari GGN, Senevirathna JDM. 2020. Plastic pollution in the
marine environment. Heliyon. 6:e04709.
128 Hens B, Hens L. 2017. Persistent threats by persistent pollu-
tants: chemical nature, concerns and future policy regarding
PCBs—what are we heading for? Toxics. 6:1.
129 Sonone SS, Jadhav S, Sankhla MS, Kumar R. 2020. Water con-
tamination by heavy metals and their toxic effect on aquacul-
ture and human health through food chain. Lett Appl
NanoBioScience. 10:2148–2166.
130 Pitcher GC, Jacinto GS. 2019. Ocean deoxygenation links to
harmful algal blooms. In: Laffoley D, Baxter JM, editors. Ocean
deoxygenation: everyone’s Problem: causes, impacts, consequences
and solutions. Gland (Switzerland): IUCN. p. 153–170.
131 Bennett NJ. 2018. Navigating a just and inclusive path towards
sustainable oceans. Mar Policy. 97:139