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Abstract

Twenty-five years ago, the Union of Concerned Scientists and more than 1700 independent scientists, including the majority of living Nobel laureates in the sciences, penned the 1992 “World Scientists’ Warning to Humanity” (see supplemental file S1). These concerned professionals called on humankind to curtail environmental destruction and cautioned that “a great change in our stewardship of the Earth and the life on it is required, if vast human misery is to be avoided.” In their manifesto, they showed that humans were on a collision course with the natural world. They expressed concern about current, impending, or potential damage on planet Earth involving ozone depletion, freshwater availability, marine life depletion, ocean dead zones, forest loss, biodiversity destruction, climate change, and continued human population growth. They proclaimed that fundamental changes were urgently needed to avoid the consequences our present course would bring. The authors of the 1992 declaration feared that humanity was pushing Earth's ecosystems beyond their capacities to support the web of life. They described how we are fast approaching many of the limits of what the ­biosphere can tolerate ­without ­substantial and irreversible harm. The scientists pleaded that we stabilize the human population, describing how our large numbers—swelled by another 2 billion people since 1992, a 35 percent increase—exert stresses on Earth that can overwhelm other efforts to realize a sustainable future (Crist et al. 2017). They implored that we cut greenhouse gas (GHG) emissions and phase out fossil fuels, reduce deforestation, and reverse the trend of collapsing biodiversity.
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https://academic.oup.com/bioscience XXXX XXXX / Vol. XX No. X BioScience 1
World Scientists’ Warning to Humanity:
A Second Notice
WILLIAM J. RIPPLE, CHRISTOPHER WOLF, THOMAS M. NEWSOME, MAURO GALETTI, MOHAMMED ALAMGIR, EILEEN CRIST,
MAHMOUD I. MAHMOUD, WILLIAM F. LAURANCE, and 15,364 scientist signatories from 184 countries
Twenty-five years ago, the Union
of Concerned Scientists and more
than 1700 independent scientists,
including the majority of living Nobel
laureates in the sciences, penned the
1992 “World Scientists’ Warning to
Humanity” (see supplemental file S1).
These concerned professionals called
on humankind to curtail environmen-
tal destruction and cautioned that
“a great change in our stewardship of
the Earth and the life on it is required,
if vast human misery is to be avoided.
In their manifesto, they showed that
humans were on a collision course
with the natural world. They expressed
concern about current, impending,
or potential damage on planet Earth
involving ozone depletion, freshwa-
ter availability, marine life depletion,
ocean dead zones, forest loss, biodiver-
sity destruction, climate change, and
continued human population growth.
They proclaimed that fundamental
changes were urgently needed to avoid
the consequences our present course
would bring.
The authors of the 1992 declara-
tion feared that humanity was pushing
Earth’s ecosystems beyond their capac-
ities to support the web of life. They
described how we are fast approach-
ing many of the limits of what the
biosphere can tolerate without
substantial and irreversible harm.
The scientists pleaded that we stabi-
lize the human population, describing
how our large numbers—swelled by
another 2 billion people since 1992,
a 35 percent increase—exert stresses
on Earth that can overwhelm other
efforts to realize a sustainable future
(Crist et al. 2017). They implored that
we cut greenhouse gas (GHG) emis-
sions and phase out fossil fuels, reduce
deforestation, and reverse the trend of
collapsing biodiversity.
On the twenty-fifth anniversary of
their call, we look back at their warn-
ing and evaluate the human response
by exploring available time-series
data. Since 1992, with the exception
of stabilizing the stratospheric ozone
layer, humanity has failed to make
sufficient progress in generally solv-
ing these foreseen environmental chal-
lenges, and alarmingly, most of them
are getting far worse (figure 1, file S1).
Especially troubling is the current
trajectory of potentially catastrophic
climate change due to rising GHGs
from burning fossil fuels (Hansen etal.
2013), deforestation (Keenan et al.
2015), and agricultural production—
particularly from farming ruminants
for meat consumption (Ripple et al.
2014). Moreover, we have unleashed
a mass extinction event, the sixth in
roughly 540 million years, wherein
many current life forms could be
annihilated or at least committed to
extinction by the end of this century.
Humanity is now being given a
second notice, as illustrated by these
alarming trends (figure 1). We are
jeopardizing our future by not reining
in our intense but geographically and
demographically uneven material
consumption and by not perceiving
continued rapid population growth as a
primary driver behind many ecological
and even societal threats (Crist et al.
2017). By failing to adequately limit
population growth, reassess the role
of an economy rooted in growth,
reduce greenhouse gases, incentivize
renewable energy, protect habitat,
restore ecosystems, curb pollution, halt
defaunation, and constrain invasive
alien species, humanity is not taking
the urgent steps needed to safeguard
our imperilled biosphere.
As most political leaders respond to
pressure, scientists, media influencers,
and lay citizens must insist that their
governments take immediate action
as a moral imperative to current and
future generations of human and other
life. With a groundswell of organized
grassroots efforts, dogged opposition
can be overcome and political leaders
compelled to do the right thing. It is
also time to re-examine and change
our individual behaviors, including
limiting our own reproduction (ideally
to replacement level at most) and
drastically diminishing our per capita
consumption of fossil fuels, meat, and
other resources.
The rapid global decline in ozone-
depleting substances shows that we
can make positive change when we
act decisively. We have also made
advancements in reducing extreme
poverty and hunger (www.worldbank.
org). Other notable progress (which
does not yet show up in the global
data sets in figure 1) include the
rapid decline in fertility rates in many
regions attributable to investments in
girls’ and womens education (www.
un.org/esa/population), the promising
decline in the rate of deforestation in
some regions, and the rapid growth
in the renewable-energy sector. We
have learned much since 1992, but
the advancement of urgently needed
changes in environmental policy,
human behavior, and global inequities
is still far from sufficient.
Sustainability transitions come
about in diverse ways, and all require
civil-society pressure and evidence-
based advocacy, political leadership,
and a solid understanding of policy
Viewpoint
2 BioScience XXXX XXXX / Vol. XX No. X https://academic.oup.com/bioscience
Figure 1. Trends over time for environmental issues identified in the 1992 scientists’ warning to humanity. The years
before and after the 1992 scientists’ warning are shown as gray and black lines, respectively. Panel(a) shows emissions
of halogen source gases, which deplete stratospheric ozone, assuming a constant natural emission rate of 0.11 Mt CFC-
11-equivalent per year. In panel (c), marine catch has been going down since the mid-1990s, but at the same time, fishing
effort has been going up (supplemental file S1). The vertebrate abundance index in panel(f) has been adjusted for
taxonomic and geographic bias but incorporates relatively little data from developing countries, where there are the fewest
studies; between 1970 and 2012, vertebrates declined by 58 percent, with freshwater, marine, and terrestrial populations
declining by 81, 36, and 35 percent, respectively (file S1). Five-year means are shown in panel(h). In panel(i), ruminant
livestock consist of domestic cattle, sheep, goats, and buffaloes. Note that y-axes do not start at zero, and it is important to
inspect the data range when interpreting each graph. Percentage change, since 1992, for the variables in each panel are as
follows: (a) –68.1%; (b) –26.1%; (c) –6.4%; (d) +75.3%; (e) –2.8%; (f) –28.9%; (g) +62.1%; (h) +167.6%; and (i) humans:
+35.5%, ruminant livestock: +20.5%. Additional descriptions of the variables and trends, as well as sources for figure 1,
are included in file S1.
Humans
Ruminant livestock
CO2 emissions
(Gt CO2 per year)
Temperature change
(°C)
Population
(billion individuals)
Dead zones (number
of affected regions)
Total forest
(billion ha)
Vertebrate species
abundance (% of 1970)
Ozone depletors (Mt CFC−
11−equivalent per year)
Freshwater resources
per capita (1000 m3)
Reconstructed marine
catch (Mt per year)
1960 1992 2016 1960 1992 2016 1960 1992 2016
50
70
90
110
130
40
60
80
100
3
4
5
6
7
6
8
10
12
4.00
4.05
4.10
0.00
0.25
0.50
0.75
1.00
0.3
0.6
0.9
1.2
1.5
200
400
600
10
20
30
Year
g. h. i.
d. e. f.
a. b. c.
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https://academic.oup.com/bioscience XXXX XXXX / Vol. XX No. X BioScience 3
instruments, markets, and other driv-
ers. Examples of diverse and effective
steps humanity can take to transition
to sustainability include the follow-
ing (not in order of importance or
urgency): (a) prioritizing the enact-
ment of connected well-funded and
well-managed reserves for a significant
proportion of the worlds terrestrial,
marine, freshwater, and aerial habi-
tats; (b) maintaining natures ecosys-
tem services by halting the conversion
of forests, grasslands, and other native
habitats; (c) restoring native plant
communities at large scales, particu-
larly forest landscapes; (d) rewilding
regions with native species, especially
apex predators, to restore ecological
processes and dynamics; (e) devel-
oping and adopting adequate policy
instruments to remedy defaunation,
the poaching crisis, and the exploi-
tation and trade of threatened spe-
cies; (f) reducing food waste through
education and better infrastructure;
(g) promoting dietary shifts towards
mostly plant-based foods; (h) further
reducing fertility rates by ensuring
that women and men have access to
education and voluntary family-plan-
ning services, especially where such
resources are still lacking; (i) increas-
ing outdoor nature education for
children, as well as the overall engage-
ment of society in the appreciation
of nature; (j) divesting of monetary
investments and purchases to encour-
age positive environmental change;
(k) devising and promoting new green
technologies and massively adopting
renewable energy sources while phas-
ing out subsidies to energy production
through fossil fuels; (l) revising our
economy to reduce wealth inequality
and ensure that prices, taxation, and
incentive systems take into account
the real costs which consumption pat-
terns impose on our environment; and
(m) estimating a scientifically defen-
sible, sustainable human population
size for the long term while rallying
nations and leaders to support that
vital goal.
To prevent widespread misery
and catastrophic biodiversity
loss, humanity must practice a
more environmentally sustainable
alternative to business as usual. This
prescription was well articulated by
the world’s leading scientists 25 years
ago, but in most respects, we have not
heeded their warning. Soon it will be
too late to shift course away from our
failing trajectory, and time is running
out. We must recognize, in our day-
to-day lives and in our governing
institutions, that Earth with all its life
is our only home.
Epilogue
We have been overwhelmed with the
support for our article and thank the
more than 15,000 signatories from all
ends of the Earth (see supplemental
file S2 for list of signatories). As far as
we know, this is the most scientists to
ever co-sign and formally support a
published journal article. In this paper,
we have captured the environmental
trends over the last 25 years, showed
realistic concern, and suggested a few
examples of possible remedies. Now,
as an Alliance of World Scientists
( scientists.forestry.oregonstate.edu) and
with the public at large, it is important
to continue this work to document chal-
lenges, as well as improved situations,
and to develop clear, trackable, and
practical solutions while communicat-
ing trends and needs to world leaders.
Working together while respecting the
diversity of people and opinions and
the need for social justice around the
world, we can make great progress for
the sake of humanity and the planet on
which we depend.
Spanish, Portuguese, and French
versions of this article can be found
in file S1.
Acknowledgments
Peter Frumhoff and Doug Boucher
of the Union of Concerned Scientists,
as well as the following individuals,
provided thoughtful discussions,
comments, or data for this paper: Stuart
Pimm, David Johns, David Pengelley,
Guillaume Chapron, Steve Montzka,
Robert Diaz, Drik Zeller, Gary
Gibson, Leslie Green, Nick Houtman,
Peter Stoel, Karen Josephson, Robin
Comforto, Terralyn Vandetta, Luke
Painter, Rodolfo Dirzo, Guy Peer, Peter
Haswell, and Robert Johnson.
Supplemental material
Supplementary data are available at
BIOSCI online including supplemental
file 1 and supplemental file 2 (full list
of all 15,364 signatories).
References cited
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William J. Ripple (bill.ripple@oregonstate.edu),
Christopher Wolf, and Thomas M. Newsome
are affiliated with the Global Trophic Cascades
Program in the Department of Forest Ecosystems
and Society at Oregon State University, in
Corvallis. TMN is also affiliated with the Centre
for Integrative Ecology at Deakin University, in
Geelong, Australia, and the School of Life and
Environmental Sciences at The University of
Sydney, Australia. Mauro Galetti is affiliated
with the Instituto de Biociências, Universidade
Estadual Paulista, Departamento de Ecologia,
in São Paulo, Brazil. Mohammed Alamgir
is affiliated with the Institute of Forestry and
Environmental Sciences at the University of
Chittagong, in Bangladesh. Eileen Crist is
affiliated with the Department of Science and
Technology in Society at Virginia Tech, in
Blacksburg. Mahmoud I. Mahmoud is affiliated
with the ICT/Geographic Information Systems
Unit of the National Oil Spill Detection and
Response Agency (NOSDRA), in Abuja, Nigeria.
William F. Laurance is affiliated with the Centre
for Tropical Environmental and Sustainability
Science and the College of Science and
Engineering at James Cook University, in Cairns,
Queensland, Australia.
doi:10.1093/biosci/bix125
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We assess climate impacts of global warming using ongoing observations and paleoclimate data. We use Earth's measured energy imbalance, paleoclimate data, and simple representations of the global carbon cycle and temperature to define emission reductions needed to stabilize climate and avoid potentially disastrous impacts on today's young people, future generations, and nature. A cumulative industrial-era limit of ∼500 GtC fossil fuel emissions and 100 GtC storage in the biosphere and soil would keep climate close to the Holocene range to which humanity and other species are adapted. Cumulative emissions of ∼1000 GtC, sometimes associated with 2°C global warming, would spur "slow" feedbacks and eventual warming of 3-4°C with disastrous consequences. Rapid emissions reduction is required to restore Earth's energy balance and avoid ocean heat uptake that would practically guarantee irreversible effects. Continuation of high fossil fuel emissions, given current knowledge of the consequences, would be an act of extraordinary witting intergenerational injustice. Responsible policymaking requires a rising price on carbon emissions that would preclude emissions from most remaining coal and unconventional fossil fuels and phase down emissions from conventional fossil fuels.
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The area of land covered by forest and trees is an important indicator of environmental condition. This study presents and analyses results from the Global Forest Resources Assessment 2015 (FRA 2015) of the Food and Agriculture Organization of the United Nations. FRA 2015 was based on responses to surveys by individual countries using a common reporting framework, agreed definitions and reporting standards. Results indicated that total forest area declined by 3%, from 4128 M ha in 1990 to 3999 M ha in 2015. The annual rate of net forest loss halved from 7.3 M ha y−1 in the 1990s to 3.3 M ha y−1 between 2010 and 2015. Natural forest area declined from 3961 M ha to 3721 M ha between 1990 and 2015, while planted forest (including rubber plantations) increased from 168 M ha to 278 M ha. From 2010 to 2015, tropical forest area declined at a rate of 5.5 M ha y−1 – only 58% of the rate in the 1990s – while temperate forest area expanded at a rate of 2.2 M ha y−1. Boreal and sub-tropical forest areas showed little net change. Forest area expanded in Europe, North America, the Caribbean, East Asia, and Western-Central Asia, but declined in Central America, South America, South and Southeast Asia and all three regions in Africa. Analysis indicates that, between 1990 and 2015, 13 tropical countries may have either passed through their forest transitions from net forest loss to net forest expansion, or continued along the path of forest expansion that follows these transitions. Comparing FRA 2015 statistics with the findings of global and pan-tropical remote-sensing forest area surveys was challenging, due to differences in assessment periods, the definitions of forest and remote sensing methods. More investment in national and global forest monitoring is needed to provide better support for international initiatives to increase sustainable forest management and reduce forest loss, particularly in tropical countries.
Ruminants, climate change and climate policy
  • W J Ripple
  • P Smith
  • H Haberl
  • S A Montzka
  • C Mcalpine
  • D H Boucher
Ripple WJ, Smith P, Haberl H, Montzka SA, McAlpine C, Boucher DH. 2014. Ruminants, climate change and climate policy. Nature Climate Change 4: 2-5. doi:10.1038/ nclimate2081
Newsome are affiliated with the Global Trophic Cascades
  • William J Ripple
William J. Ripple (bill.ripple@oregonstate.edu), Christopher Wolf, and Thomas M. Newsome are affiliated with the Global Trophic Cascades