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The Anthropocene is recognized (though not yet formally defined) as the time when human impacts are widespread on Earth. While some of the impacts are essential to supporting large human populations and can be sustainable in the long run, others can irretrievably damage the life support systems upon which the global society has come to depend, or spark rapid changes to which societies cannot adapt fast enough. Among these dangerous trends are increasing climate disruption, extinctions, loss of non-human-dominated ecosystems, pollution, and population overgrowth. Interactions between these five trends exacerbate their potential to trigger harmful global change. Reducing the resultant risks requires effective cooperation between scientists and policy makers to develop strategies that guide for environmental health over the next few decades. To that end, the Scientific Consensus on Maintaining Humanity’s Life Support Systems in the 21st Century was written to make accessible to policy makers and others the basic scientific underpinnings and widespread agreement about both the dangers of and the solutions to climate disruption, extinctions, ecosystem loss, pollution and population overgrowth. When it was released in May 2013, the document included endorsements by 522 global change scientists, including dozens of members of various nations’ most highly recognized scientific bodies, from 41 countries around the world. Since then, endorsements have grown to more than 1300 scientists plus more than 1700 others – business people, NGO representatives, students, and the general public – spanning more than 60 countries. Now also available in Spanish and Chinese, the document has proven useful in helping to stimulate national and international agreements. Further information about the genesis, uses, the signatories, and how to endorse it can be found at http://consensusforaction.stanford.edu/. Such communication between scientists, policy makers, and the public at large will be essential for effective guidance to address global change as the Anthropocene progresses.
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The Anthropocene Review
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The online version of this article can be found at:
DOI: 10.1177/2053019613516290
2014 1: 78The Anthropocene Review
Wake
John Peterson Myers, Rosamond L Naylor, Stephen Palumbi, Nils Chr Stenseth and Marvalee H
Ehrlich, Jussi T Eronen, Mikael Fortelius, Elizabeth A Hadly, Estella B Leopold, Harold A Mooney,
Anthony D Barnosky, James H Brown, Gretchen C Daily, Rodolfo Dirzo, Anne H Ehrlich, Paul R
Systems in the 21st Century: Information for Policy Makers
Scientific Consensus on Maintaining Humanity's Life SupportIntroducing the
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The Anthropocene Review
2014, Vol. 1(1) 78 –109
© The Author(s) 2014
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DOI: 10.1177/2053019613516290
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Review
Introducing the Scientific
Consensus on Maintaining
Humanity’s Life Support Systems
in the 21st Century: Information
for Policy Makers
Anthony D Barnosky,
1
James H Brown,
2
Gretchen C Daily,
3
Rodolfo Dirzo,
3
Anne H
Ehrlich,
3
Paul R Ehrlich,
3
Jussi T Eronen,
4
Mikael
Fortelius,
4
Elizabeth A Hadly,
3
Estella B
Leopold,
5
Harold A Mooney,
3
John Peterson
Myers,
6
Rosamond L Naylor,
3
Stephen Palumbi,
3
Nils Chr Stenseth
7
and Marvalee H Wake
1
Abstract
The Anthropocene is recognized (though not yet formally defined) as the time when human
impacts are widespread on Earth. While some of the impacts are essential to supporting large
human populations and can be sustainable in the long run, others can irretrievably damage the life
support systems upon which the global society has come to depend, or spark rapid changes to
which societies cannot adapt fast enough. Among these dangerous trends are increasing climate
disruption, extinctions, loss of non-human-dominated ecosystems, pollution, and population
overgrowth. Interactions between these five trends exacerbate their potential to trigger harmful
global change. Reducing the resultant risks requires effective cooperation between scientists
and policy makers to develop strategies that guide for environmental health over the next few
decades. To that end, the Scientific Consensus on Maintaining Humanity’s Life Support Systems in
the 21st Century was written to make accessible to policy makers and others the basic scientific
underpinnings and widespread agreement about both the dangers of and the solutions to climate
disruption, extinctions, ecosystem loss, pollution and population overgrowth. When it was
released in May 2013, the document included endorsements by 522 global change scientists,
including dozens of members of various nations’ most highly recognized scientific bodies, from
1
University of California, USA
2
University of New Mexico, USA
3
Stanford University, USA
4
University of Helsinki, Finland
5
University of Washington, USA
6
Environmental Health Sciences, USA
7
University of Oslo, Norway
Corresponding author:
Anthony D Barnosky, Department of Integrative Biology,
University of California, 1005 Valley Life Sciences Bldg
#3140, Berkeley CA 94720, USA.
Email: barnosky@berkeley.edu
516290ANR
0010.1177/2053019613516290The Anthropocene ReviewBarnosky et al.
research-article2014
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Barnosky et al. 79
41 countries around the world. Since then, endorsements have grown to more than 1300
scientists plus more than 1700 others – business people, NGO representatives, students, and the
general public – spanning more than 60 countries. Now also available in Spanish and Chinese, the
document has proven useful in helping to stimulate national and international agreements. Further
information about the genesis, uses, the signatories, and how to endorse it can be found at
http://consensusforaction.stanford.edu/. Such communication between scientists, policy makers,
and the public at large will be essential for effective guidance to address global change as the
Anthropocene progresses.
Keywords
climate change, ecosystem loss, extinction, pollution, population growth
Essential points for policy makers
Scientific Consensus on Maintaining Humanity’s Life Support Systems in the 21st
Century
Earth is rapidly approaching a tipping point (Figure 1). Human impacts are causing alarming levels
of harm to our planet. As scientists who study the interaction of people with the rest of the bio-
sphere using a wide range of approaches, we agree that the evidence that humans are damaging
their ecological life support systems is overwhelming.
We further agree that, based on the best scientific information available, human quality of life
will suffer substantial degradation by the year 2050 if we continue on our current path.
Science unequivocally demonstrates the human impacts of key concern:
Climate disruption – more, faster climate change than since humans first became a
species.
Extinctions – not since the dinosaurs became extinct have so many species and populations
died out so fast, both on land and in the oceans.
Wholesale loss of diverse ecosystems – we have plowed, paved, or otherwise transformed
more than 40% of Earth’s ice-free land, and no place on land or in the sea is free of our direct
or indirect influences.
Pollution – environmental contaminants in the air, water and land are at record levels and
increasing, seriously harming people and wildlife in unforeseen ways.
Human population growth and consumption patterns – the population, which stands at 7
billion people alive today, will likely grow to 9.5 billion by 2050, and the pressures of heavy
material consumption among the middle class and wealthy may well intensify.
By the time today’s children reach middle age, it is extremely likely that Earth’s life support
systems, critical for human prosperity and existence, will be irretrievably damaged by the magni-
tude, global extent, and combination of these human-caused environmental stressors, unless we
take concrete, immediate actions to ensure a sustainable, high-quality future.
As members of the scientific community actively involved in assessing the biological and soci-
etal impacts of global change, we are sounding this alarm to the world. For humanity’s continued
health and prosperity, we all – individuals, businesses, political leaders, religious leaders,
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80 The Anthropocene Review 1(1)
scientists, and people in every walk of life – must work hard to solve these five global problems,
starting today:
1. climate disruption
2. extinctions
3. loss of ecosystem diversity
4. pollution
5. human population growth and resource consumption
Purpose of this Consensus statement
Since about 1950, the world has been changing faster, and to a greater extent, than it has in the past
12,000 years. Balancing the positive changes against the negative ones will be the key challenge of
the 21st century.
Figure 1. Many indicators suggest that Earth is poised at a critical transition, or ‘tipping point’, that may
cause widespread disruptions in natural landscapes and societal functions we now take for granted.
Source: Cheng (Lily) Li.
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Barnosky et al. 81
Positive change has included the Green Revolution, which reduced world hunger (although one
in eight people still do not have enough to eat); new medical breakthroughs that have reduced
infant and childhood mortality and allow people to live longer and more productive lives; access
to myriad goods and services that increase wealth and comfort levels; and new technological
breakthroughs, such as computers, cell phones, and the internet, that now connect billions of peo-
ple throughout the world into a potential global brain.
In contrast, other changes, all interacting with each other, are leading humanity in dangerous
directions: climate disruption, extinction of biodiversity, wholesale loss of vast ecosystems, pollu-
tion, and ever-increasing numbers of people competing for the planet’s resources. Until now, these
have often been viewed as ‘necessary evils’ for progress, or collateral damage that, while unfortu-
nate, would not ultimately stand in the way of serving the needs of people.
Several recent comprehensive reports by the scientific community, however, have now shown
otherwise. Rather than simply being inconveniences, the accelerating trends of climate disruption,
extinction, ecosystem loss, pollution, and human population growth in fact are threatening the life
support systems upon which we all depend for continuing the high quality of life that many people
already enjoy and to which many others aspire.
The vast majority of scientists who study the interactions between people and the rest of the
biosphere agree on a key conclusion: that the five interconnected dangerous trends listed above are
having detrimental effects and, if continued, the already-apparent negative impacts on human qual-
ity of life will become much worse within a few decades. The multitude of sound scientific evi-
dence to substantiate this has been summarized in many recent position papers and consensus
statements (a few samples are listed at the end of the References section), and documented in
thousands of articles in the peer-reviewed scientific literature. However, the position papers and
consensus statements typically focus only on one or a subset of the five key issues (for example,
climate change, or biodiversity loss, or pollution), and access to the peer-reviewed literature is
often difficult for non-scientists. As a result, policy makers faced with making critical decisions
can find it cumbersome both to locate the pertinent information and to digest the thousands of
pages through which it is distributed.
Here we provide a summary intended to:
 be useful to policy makers and others who need to understand the most serious environmental-
health issues that affect both local constituencies and the entire planet
 clearly voice the consensus of most scientists who study these issues that:
climate disruption, extinction, ecosystem loss, pollution, and population growth are seri-
ous threats to humanity’s wellbeing and societal stability, and
these five major threats do not operate independently of each other.
We also outline broad-brush actions that, from a scientific perspective, will be required to miti-
gate the threats. The intent is to provide information that will be necessary and useful if the desire
of the general public, governments, and businesses is to maximize the chance that the world of our
children and grandchildren will be at least as good as the one in which we live now.
Overview of problems and broad-brush solutions
Climate disruption
Reduce effects of climate disruption by decreasing greenhouse gas emissions, and by implementing
adaptation strategies to deal with the consequences of climate change already underway. Viable
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82 The Anthropocene Review 1(1)
approaches include accelerating development and deployment of carbon-neutral energy tech-
nologies to replace fossil fuels; making buildings, transportation, manufacturing systems, and
settlement patterns more energy-efficient; and conserving forests and regulating land conver-
sion to maximize carbon sequestration. Adapting to the inevitable effects of climate change
will be crucial for coastal areas threatened by sea-level rise; ensuring adequate water supplies
to many major population centers; maintaining agricultural productivity; and managing biodi-
versity and ecosystem reserves.
Extinctions
Slow the very high extinction rates that are leading to a global loss of biodiversity. Viable approaches
include assigning economic valuation to the ways natural ecosystems contribute to human wellbe-
ing and managing all ecosystems, both in human-dominated regions and in regions far from direct
human influence, to sustain and enhance biodiversity and ecosystem services. It will be critical to
develop cross-jurisdictional cooperation to recognize and mitigate the interactions of global pres-
sures (for example, climate change, ocean acidification) and local pressures (land transformation,
overfishing, poaching endangered species, etc.).
Ecosystem transformation
Minimize transformation of Earth’s remaining natural ecosystems into farms, suburbs, and other human
constructs. Viable agricultural approaches include increasing efficiency in existing food-producing
areas; improving food-distribution systems; and decreasing waste. Viable development approaches
include enhancing urban landscapes to accommodate growth rather than encouraging suburban
sprawl; siting infrastructure to minimize impacts on natural ecosystems; and investing in vital
‘green infrastructure’, such as through restoring wetlands, oyster reefs, and forests to secure water
quality, flood control, and boost access to recreational benefits.
Pollution
Curb the manufacture and release of toxic substances into the environment. Viable approaches include
using current science about the molecular mechanisms of toxicity and applying the precautionary
principle (verification of no harmful effects) to guide regulation of existing chemicals and design
of new ones. We have the knowledge and ability to develop a new generation of materials that are
inherently far safer than what is available today.
Population growth and consumption
Bring world population growth to an end as early as possible and begin a gradual decline. An achievable
target is no more than 8.5 billion people by 2050 and a peak population size of no more than 9 bil-
lion, which through natural demographic processes can decrease to less than 7 billion by 2100.
Viable approaches include ensuring that everyone has access to education, economic opportuni-
ties, and healthcare, including family planning services, with a special focus on women’s rights.
Decrease per-capita resource use, particularly in developed countries. Viable approaches include
improving efficiency in production, acquisition, trade, and use of goods and promoting environ-
mentally friendly changes in consumer behavior.
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Barnosky et al. 83
Planning for the future
Overall, we urge the use of the best science available to anticipate most-likely, worst-case, and
best-case scenarios for 50 years into the future, in order to emplace policies that guide for environ-
mental health over the long term as well as adapting to immediate crises.
Background information: Dangerous trends in our life support
systems
People have basic needs for food, water, health, and a place to live, and additionally have to pro-
duce energy and other products from natural resources to maintain standards of living that each
culture considers adequate. Fulfilling all of these needs for all people is not possible in the absence
of a healthy, well-functioning global ecosystem. The ‘global ecosystem’ is basically the complex
ways that all life forms on Earth – including us – interact with each other and with their physical
environment (water, soil, air, and so on). The total of all those myriad interactions compose the
planet’s, and our, life support systems.
Humans have been an integral part of the global ecosystem since we first evolved; now we have
become the dominant species in it. As such, we strongly influence how Earth’s life support systems
work, in both positive and negative ways. A key challenge in the coming decades is to ensure that
the negative influences do not outweigh the positive ones, which would make the world a worse
place to live. Robust scientific evidence confirms that five interconnected negative trends of major
concern have emerged over the past several decades:
Disrupting the climate that we and other species depend upon.
Triggering a mass extinction of biodiversity.
Destroying diverse ecosystems in ways that damage our basic life support systems.
Polluting our land, water, and air with harmful contaminants that undermine basic biologi-
cal processes, impose severe health costs, and undermine our ability to deal with other
problems.
Increasing human population rapidly while relying on old patterns of production and
consumption.
These five trends interact with and exacerbate each other, such that the total impact becomes
worse than the simple sum of their parts.
Ensuring a future for our children and grandchildren that is at least as desirable as the life we
live now will require accepting that we have already inadvertently pushed the global ecosystem in
dangerous directions, and that we have the knowledge and power to steer it back on course – if we
act now. Waiting longer will only make it harder, if not impossible, to be successful, and will inflict
substantial, escalating costs in both monetary terms and human suffering.
The following pages summarize the causes of each of the five dangerous trends, why their con-
tinuation will harm humanity, how they interact to magnify undesirable impacts, and broad-brush
solutions necessary to move the human race toward a sustainable, enjoyable future.
Rising to the challenge
Defusing the five global crises summarized on the following pages will not be easy, but past expe-
rience demonstrates that problems of this huge scale are indeed solvable – if humanity is ready to
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84 The Anthropocene Review 1(1)
rise to the challenge. Solutions will require the same things that worked successfully in dealing
with past global crises: individual initiative, cooperation both within and across national bounda-
ries, technological advances, and emplacing new infrastructure. Individual initiative has seldom
been in short supply and continues to be a powerful human resource. Successful global-through-
local cooperation resulted in ending World War II and rebuilding afterwards; banning use of nuclear
weapons; dramatically increasing global food production with the Green Revolution and averting
food crises through United Nations initiatives; greatly reducing the use of persistent toxic chemi-
cals such as DDT; reversing stratospheric ozone depletion (the ‘ozone hole’); and diminishing
infectious diseases such as malaria and polio worldwide.
Likewise, past technological advances and the building of new infrastructure have been remark-
able and commensurate in scale with what is needed to fix today’s problems. For instance, in just
7 years, responding to the demands of World War II, the USA built its airplane fleet from about
3100 to 300,000 planes, and beginning in the 1950s, took less than 50 years to build 47,000 miles
(75,639 km) of interstate highways – enough paved roads to encircle Earth almost twice. Over
about the same time, 60% of the world’s largest rivers were re-plumbed with dams. In about 30
years, the world went from typewriters and postage stamps to hand-held computers and the inter-
net, now linking one-third of the world’s population. During the same time we leapfrogged from
about 310 million dial-up, landline phones to 6 billion mobile phones networked by satellites and
presently connecting an estimated 3.2 billion people.
In the context of such past successes, the current problems of climate disruption, extinction,
ecosystem loss, pollution, and growing human population and consumption are not too big to solve
in the coming 30 to 50 years. Indeed, the scientific, technological, and entrepreneurial pieces are in
place, and encouraging initiatives and agreements have begun to emerge at international, national,
state, and local levels. Moreover, today’s global connectivity is unprecedented in the history of the
world, offering the new opportunity for most of the human population to learn of global problems
and to help coordinate solutions.
Three key lessons emerge from the examples given above. The first is that global-scale prob-
lems must be acknowledged before they can be solved. The second is that fixing them is eminently
possible through ‘win-win’ interactions between local communities, where solutions are actually
developed and always emplaced, and higher levels of government, which define priorities backed
by clear incentives. The third very important lesson is that big problems cannot be fixed overnight.
Given inherent lag times in changing climate, building infrastructure, changing societal norms, and
slowing population growth, actions taken today will only begin to bear full fruit in a few decades.
If, for example, we move most of the way towards a carbon-neutral energy system by 2035, climate
still will not stabilize before 2100, and it will still be a different climate than we are used to now.
But, if we delay action to 2035, not only will climate disruption continue to worsen, but efforts at
mitigation and adaptation will cost dramatically more; climate would not stabilize until well after
the year 2100, and when it did, it would be at an average climate state that is far more disruptive to
society than would have been the case if we had acted earlier. Similar costs of delay accrue for the
other problems as well; indeed, delaying action on those problems will lead to irretrievable losses
of species, ecosystems, and human health and prosperity. Starting today to diffuse the global crises
we now face is therefore crucial.
Climate disruption
It is now clear that people are changing Earth’s climate by adding greenhouse gases to the
atmosphere primarily through the burning of coal, oil (and its by-products such as gasoline,
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Barnosky et al. 85
diesel, etc.), and natural gas (Figure 2). The overall trend, still continuing, has been to raise the
average temperature of the planet over the course of the last century, and especially the last 60
years. Raising average global temperature causes local changes in temperature, in amount and
timing of rainfall and snowfall, in length and character of seasons, and in the frequency of
extreme storms, floods, droughts, and wildfires (IPCC, 2007, 2012). Sea-level rise is a particu-
lar concern in coastal areas (IPCC, 2007, 2012; Pfeffer et al., 2008; Rahmstorf, 2007). Such
impacts directly influence the wellbeing of people through damaging their livelihoods, prop-
erty, and health, and indirectly through increasing potentials for societal conflict. Recent exam-
ples include the flooding from superstorm Sandy on the east coast of the USA, record wildfires
Figure 2. The main greenhouse gases emitted by human activities are carbon dioxide (CO
2
), methane
(CH
4
) and nitrous oxide (NO). Of these, CO
2
is particularly important because of its abundance. Human-
produced ozone-forming chemicals also are contributing to climate change.
Source: AD Barnosky.
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86 The Anthropocene Review 1(1)
and drought throughout the western USA and Australia, heat waves and drought in Europe, and
floods in Pakistan, all of which occurred in 2012 and 2013.
Causes for concern
Even best-case emissions scenarios (the IPCC B1 scenario) (IPCC, 2007) project that Earth will be
hotter than the human species has ever seen by the year 2070, possibly sooner (Barnosky et al.,
2012; IPCC, 2007). Continuing current emission trends (PriceWaterhouseCoopersLLP, 2012)
would, by the time today’s children grow up and have grandchildren (the year 2100), likely cause
average global temperature to rise between 4.3°F and 11.5°F (2.4–6.4°C), with a best estimate
being 7.2°F (4°C) (IPCC, 2007). The last time average global temperature was 7.2°F hotter was
some 14 million years ago. The last time it was 11.5°F hotter was about 38 million years ago
(Zachos et al., 2008). [Note: The IPCC AR5 report was released after this document was written;
its RCP 8.5 scenario suggests a mean warming of 6.7°F (3.7°C) by 2100, with a likely range of
4.7–8.6°F (2.6–4.8°C) (IPCC, 2013)].
Impacts that would be detrimental to humanity by 2100, if not before, should greenhouse gas
emissions continue at their present pace, include the following.
Longer and more intense heat waves. The 1-in-20 year hottest day is likely to become a
1-in-2 year event by the end of the 21st century in most regions (for the IPCC B1, A1B, and
A2 emissions scenarios; IPCC, 2012). Such effects already are being observed – in 2013,
temperatures in Australia rose so much that weather maps had to add two new colors to
express the new hot extremes. Some models indicate that the current trajectory of warming,
if continued to the year 2100, would cause some areas where people now live to be too hot
for humans to survive (Sherwood and Huber, 2010). (Note: The term ‘likely’ in this context
implies that there is a 66–100% chance of the effect occurring. Usage here follows defini-
tions explained in IPCC publications.)
More frequent damaging storms. The 1-in-20 year annual maximum daily precipitation
amount is likely to become a 1-in-5 to1-in-15 year event by the end of the 21st century in
many regions (IPCC, 2012). Cyclone wind speeds are likely to increase. Cities would expe-
rience the extent of damage caused by superstorm Sandy on a more frequent basis.
Major damage to coastal cities as sea level rises. The extent of sea-level rise will depend in
part on how fast glaciers melt. Low-end projections (IPCC, 2007) call for a rise in sea level
of 0.6–1.9 feet (0.18–0.59 m) by 2100; high-end projections suggest seas rising as high as
2.6–13.1 feet (0.8–4.0 m) (Pfeffer et al., 2008; Rahmstorf, 2007; Solomon et al., 2011).
Raising sea level to even the lower estimates would flood large parts of major cities world-
wide and force the permanent resettlement of millions of people; about 100 million people
now live less than 3.3 feet (1 m) above mean sea level (Dow and Downing, 2007).
Water shortages in populous parts of the world. Cities and farmlands that rely on the sea-
sonal accumulation of snow pack and slow spring melt, arid regions that apportion water
from major rivers, and regions that depend on water from glacier melt all are at risk (Dow
and Downing, 2007).
Local reduction of crop yields. New climate patterns will change which crops can be grown
in which areas. Some regions are projected to experience overall declines: for instance,
cereal crop production is expected to fall in areas that now have the highest population den-
sity and/or the most undernourished people, notably most of Africa and India (Dow and
Downing, 2007). Key crop-growing areas, such as California, which provides half of the
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Barnosky et al. 87
fruits, nuts, and vegetables for the USA, will experience uneven effects across crops, requir-
ing farmers to adapt rapidly to changing what they plant (Kahrl and Roland-Holst, 2012;
Lobell et al., 2006).
Economic losses, social strife and political unrest. Damage to coastal areas, flooding of
ports, water shortages, adverse weather and shifts in crop-growing areas, creation of new
shipping lanes, and competition for newly accessible arctic resources all will complicate
national and international relations, and cost billions of dollars (Lobell et al., 2006; Shearer,
2005; Solomon et al., 2011; Steinbruner et al., 2012). For instance, the New York Times
reported that by the first months of 2013, United States taxpayers had already paid US$7
billion to subsidize farmers for crops that failed because of extreme drought, and that figure
was anticipated to rise as high as US$16 billion.
Spread of infectious disease. As temperate regions warm, costly and debilitating mosquito-
borne diseases such as malaria are expected to increase in both developed and developing
nations (World Health Organization (WHO), 2013a). Indeed, expansion of West Nile virus
into the USA beginning in 1999 has already occurred, and bluetongue virus, a costly live-
stock disease carried by midges, has expanded northward into central and northern Europe
in the past decade. Besides human suffering, the human-health costs caused by climate
change are anticipated to be US$2–4 billion per year by 2030 (WHO, 2013a).
Pest expansions that cause severe ecological and economic losses. For example, over the
past two decades, millions of acres of western North American forests have been killed by
pine beetles whose populations have exploded as a result of warmer winter temperatures –
previously, extreme winter cold prevented abundant beetle survival (Kurz et al., 2008). The
beetle kill reduces wood production and sales, and lowers property values in developed
areas.
Major damage to unique ecosystems. Warming and acidification of ocean water is expected
to destroy a large portion of the world’s coral reefs, essentially the ‘rainforests of the sea’,
so-called because they host most of the oceans’ biodiversity (Morel et al., 2010; Solomon
et al., 2011). On land, forests worldwide face drought-induced decline, both in dry and wet
regions (Choat et al., 2012). This is especially problematic in many tropical and subtropical
forests (Salazar et al., 2007), which are the cradles of most terrestrial biodiversity.
Extinction of species. Currently at least 20–40% of assessed species – amounting to a mini-
mum of 12,000–24,000 species – are possibly at increased risk of extinction if mean global
temperature increases 2.7–4.5°F (1.5–2.5°C) (Dow and Downing, 2007; IPCC, 2007).
Current emissions trends are on track for a 7.2°F (4°C) rise in global mean temperature by
2100, which would put many more species at risk (Solomon et al., 2011). The situation with
population extinctions is much worse, with much higher extinction rates in the basic unit of
biodiversity that supplies ecosystem services (Hughes et al., 1997).
Solutions
Avoiding the worst impacts of human-caused climate change will require reducing emissions of
greenhouse gases substantially (PriceWaterhouseCoopersLLP, 2012; Solomon et al., 2011) and
quickly (Rogelj et al., 2012). For instance, in order to stabilize atmospheric concentrations of CO
2
at 450 parts per million by the year 2050, which would give a 50% chance of holding global tem-
perature rise to 2°C, emissions would have to be decreased 5.1% per year for the next 38 years.
This rate of reduction has not been achieved in any year in the past six decades, which puts the
magnitude and urgency of the task in perspective (PriceWaterhouseCoopersLLP, 2012).
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88 The Anthropocene Review 1(1)
The world needs another industrial revolution in which our sources of energy are affordable, accessible
and sustainable. Energy efficiency and conservation, as well as decarbonizing our energy sources, are
essential to this revolution. (Chu and Majumdar, 2012)
However, reducing emissions to requisite values over the next 50 years appears possible through
coordinated innovation and deployment of new transportation and energy systems, which can be
accomplished largely with existing technology (Chu and Majumdar, 2012; Davis et al., 2013;
Jacobson and Delucchi, 2009, 2011). This will require rapid scaling up of carbon-neutral energy
production (solar, wind, hydro, geothermal, hydrogen fuel-cells, nuclear, microbe-based biofuels)
to replace energy production from fossil fuels. In the transitional decades when fossil fuels will
continue to be in widespread use, increased efficiency in energy use (better gas mileage for cars
and trucks, more energy-efficient buildings, etc.) will be necessary, as will phasing out coal-fired
power plants in favor of lower-emissions facilities (natural gas). While fossil fuels remain in use
during the transitional period, carbon capture and storage (CCS) from major emitters such as
cement and steel plants will probably be necessary. Scaling up carbon-neutral energy production
fast enough will likely require legislation and government policies designed to stimulate the right
kinds of innovations and realign the economic landscape for energy production (Chu and Majumdar,
2012; Delucchi and Jacobson, 2011).
Some effects of climate change already are underway (sea-level rise, higher frequency of
extreme weather, etc.). Plans to adapt to unavoidable climate changes will need to be developed
and implemented for cities and public lands. Keeping agricultural areas productive will require
changing the crops grown in some places, and ensuring seed stocks that are adapted to new cli-
mates. Ultimate monetary costs for climate mitigation and adaptation grow substantially each year
action is postponed (Kahrl and Roland-Holst, 2012; Rogelj et al., 2012).
Extinctions
Biological extinctions cannot be reversed and therefore are a particularly destructive kind of global
change. Even the most conservative analyses indicate that human-caused extinction of other spe-
cies is now proceeding at rates that are 3–80 times faster than the extinction rate that prevailed
before people were abundant on Earth (Barnosky et al., 2011), and other estimates are much higher
(Pimm and Raven, 2000; Pimm et al., 1995, 2006; World Resources Institute (WRI), 2005). If the
current rate of extinction is not slowed for species and their constituent populations, then within as
little as three centuries the world would see the loss of 75% of vertebrate species (mammals, birds,
reptiles, amphibians, and fish), as well as loss of many species of other kinds of animals and plants
(Barnosky et al., 2011). Earth has not seen that magnitude of extinction since an asteroid hit the
planet 65 million years ago, killing the dinosaurs and many other species. Only five times in
the 540 million years since complex life forms dominated Earth have mass extinctions occurred at
the scale of what current extinction rates would produce; those mass extinctions killed an estimated
75–96% of the species known to be living at the time.
Currently, sound scientific criteria document that at least 23,000 species are threatened with
extinction, including 22% of mammal species, 14% of birds, 29% of evaluated reptiles, as many as
43% of amphibians, 29% of evaluated fish, 26% of evaluated invertebrate animals, and 23% of
plants (Collen et al., 2012; GBO3, 2010; International Union for Conservation of Nature (IUCN),
2010). Populations – groups of interacting individuals that are the building blocks of species – are
dying off at an even faster rate than species. The extinction of local populations, in fact, represents
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the strongest pulse of contemporary biological extinction. For example, since 1970 some 30% of
all vertebrate populations have died out (McRae et al., 2012), and most species have experienced
loss of connectivity between populations because of human-caused habitat fragmentation. Healthy
species are composed of many, interconnected populations; rapid population loss, and loss of con-
nectivity between populations, are thus early warning signs of eventual species extinction.
Causes for concern
The world’s plants, animals, fungi, and microbes are the working parts of Earth’s life support sys-
tems. Losing them imposes direct economic losses, lessens the effectiveness of nature to serve our
needs (‘ecosystem services’, see below), and carries significant emotional and moral costs.
Economic losses. At least 40% of the world’s economy and 80% of the needs of the poor are
derived from biological resources (Dow and Downing, 2007). In the USA, for example, com-
mercial fisheries, some of which rely on species in which the majority of populations have
already gone extinct, provide approximately one million jobs and US$32 billion in income
annually (National Oceanic and Atmospheric Administration (NOAA), 2013b). Internationally,
ecotourism, driven largely by the opportunity to view currently threatened species such as
elephants, lions, and cheetahs, supplies 14% of Kenya’s GDP (in 2013) (United States Agency
for International Development (USAID), 2013) and 13% of Tanzania’s (in 2001), and in the
Galapagos Islands, ecotourism contributed 68% of the 78% growth in GDP that took place
from 1999 to 2005 (Taylor et al., 2008). Local economies in the USA also rely on revenues
generated by ecotourism linked to wildlife resources: for example, in the year 2010 visitors to
Yellowstone National Park, which attracts a substantial number of tourists lured by the pros-
pect of seeing wolves and grizzly bears, generated US$334 million and created more than
4800 jobs for the surrounding communities (Stynes, 2011). In 2009, visitors to Yosemite
National Park created 4597 jobs in the area, and generated US$408 million in sales revenues,
US$130 million in labor income, and US$226 million in value added (Cook, 2011).
Loss of basic services in many communities. Around the world, indigenous and rural com-
munities depend on the populations of more than 25,000 species for food, medicine, and
shelter (Dirzo and Raven, 2003).
Loss of ecosystem services. Extinctions irreversibly decrease biodiversity, which in turn
directly costs society through loss of ecosystem services (Cardinale et al., 2012; Daily et al.,
2000; Ehrlich et al., 2012). ‘Ecosystem services’ (see the quote below) are attributes of eco-
logical systems that serve people. Among the ecosystem services that support human life
and endeavors are: moderating weather; regulating the water cycle, stabilizing water sup-
plies; filtering drinking water; protecting agricultural soils and replenishing their nutrients;
disposing of wastes; pollinating crops and wild plants; providing food from wild species
(especially seafood); stabilizing fisheries; providing medicines and pharmaceuticals; con-
trolling spread of pathogens; and helping to reduce greenhouse gases in the atmosphere . In
contrast to such directly quantifiable benefits promoted by high biodiversity, reducing bio-
diversity generally reduces the productivity of ecosystems, reduces their stability, and makes
them prone to rapidly changing in ways that are clearly detrimental to humanity (Cardinale
et al., 2012). For example, among other costs, the loss of tropical biodiversity from defor-
estation often changes local or regional climate, leading to more frequent floods and
droughts and declining productivity of local agricultural systems. Tropical deforestation can
also cause new diseases to emerge in humans, because people more often encounter and
disrupt animal vectors of disease (Patz et al., 2004; Quammen, 2012).
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90 The Anthropocene Review 1(1)
The world’s ecosystems are Natural Capital that provides vital benefits called Ecosystem Services
necessary for Production of Goods (crops, timber, seafood); Life-Support Systems (provision and
purification of water, buffering against storms, floods, and droughts); Life-Fulfilling Amenities (beauty,
opportunity for recreation, and the associated physical and mental health benefits); and Options for the
future (genetic diversity for use in agriculture, energy, pharmaceuticals and other industries). Modified
from Daily et al., (2000)
Intangible values. Continuing extinction at the present pace would considerably degrade
quality of life for hundreds of millions of people who find emotional and aesthetic value in
the presence of iconic species in natural habitats. In this context species are priceless, in the
sense of being infinitely valuable. An apt metaphor is a Rembrandt or other unique work of
art that evokes exceptional human feelings, and whose loss would be generally recognized
as making humanity poorer.
Chief drivers of extinction
The main drivers of human-caused extinction as follows (Barnosky et al., 2011; GBO3, 2010;
Pimm and Raven, 2000; Pimm et al., 1995; Vié et al., 2009; WRI, 2005) (Figure 3).
Habitat destruction from ecosystem transformation. Such practices as unsustainable forestry
and conversion of land to agriculture, suburban sprawl, and roads, all cause both habitat
destruction and habitat fragmentation. In particular, logging and clearing of tropical rainfor-
ests for ranching or farming permanently destroys the habitats for vast numbers of species.
Such areas are among the most important reservoirs of terrestrial biodiversity, harboring
thousands of unique species and plant and animal functional groups (ecological niches) found
Figure 3. Extinction rates are now too high because old models of natural resource use are no longer
sustainable. Supplying 7 billion people (9.5 billion by 2050) with a high quality of life requires investing in
nature’s capital, rather than spending down its principal.
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Barnosky et al. 91
Figure 4. If current rates of elephant poaching continue, there would be no more wild elephants on
Earth within 20–30 years. (This assumes continuation of the annual rate of about 25,000 elephants killed in
2011, and a world population of between 420,000 and 650,000 African elephants plus about 50,000 Asian
elephants (IUCN, 2008).) The bulk of the short-term profits go to organized crime and terrorist groups.
In contrast, revenues from ecotourism are sustainable for the long run and contribute directly to local
economies.
Source: AD Barnosky.
nowhere else (Dirzo and Raven, 2003). In the oceans, habitat destruction and fragmentation
results from pollution, trawling, shipping traffic, and shipping noise (sonar, etc.).
Environmental Contamination. Environmental contamination from human-made chemicals
contributes to extinction pressures by destroying habitats (for instance, mine dumps, oil
spills and agricultural runoff), by direct toxic effects of pollutants, and through subtle effects
on animals’ immune and reproductive systems.
Climate change. Extinctions result when species cannot move fast enough to find climatic
refuges as the climate becomes unsuitable where they now live; when climate changes such
that it exceeds their physiological, developmental, or evolutionary tolerances; or when criti-
cal species interactions (the way one species depends on the next) are disrupted (Cahill
et al., 2012). On land, models predict that by the year 2100, between 12% and 39% of the
planet will have developed climates that no living species has ever experienced, and con-
versely, the climate that many species currently live in will disappear from 10% to 48% of
Earth’s surface (Williams et al., 2007). These changes will be most pronounced in areas that
currently harbor most of the world’s biodiversity. In the oceans, acidification, a by-product
of climate change that disrupts growth and development of marine organisms, is of particu-
lar concern, because it prevents marine shelly animals such as clams and oysters from build-
ing their shell, and causes collapse of the physical reef infrastructure on which most marine
species ultimately depend.
Intensive exploitation of wild species for profit. Some iconic species, such as elephants
(Figure 4), rhinoceroses, and tigers are being hunted to extinction to sell their tusks, horns,
or other body parts to be made into curios or for purported health products. For example, the
demand for ivory from elephant tusks, primarily from Asian markets, has driven the price
high enough that elephant poaching has now become a lucrative source of income for inter-
national crime rings and terrorist organizations. Other species are being overutilized as mar-
ketable food – this is especially a problem for many ocean fisheries, such as those for
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92 The Anthropocene Review 1(1)
Bluefin tuna and Atlantic cod. Demand is outstripping supply for such species – there are
now seven times as many humans on the planet as there are wild salmon (Greenburg, 2011).
In the same vein, the dramatic and rapid clearing of rainforests is motivated by immediate
economic yield. In all of these cases, the one-time gain in profit (which benefits relatively
few people) is a pittance compared with the loss of natural capital, which supplies important
benefits locally and globally for the long term. In economic terms, it is analogous to spend
down the principal of an investment rather than living off the interest.
Many actions in support of biodiversity have had significant and measurable results in particular areas
and amongst targeted species and ecosystems. This suggests that with adequate resources and political
will, the tools exist for loss of biodiversity to be reduced at wider scales. (GBO3, 2010)
Solutions
Because species losses accrue from global pressures, and species and ecosystem distributions tran-
scend political boundaries, solutions to the extinction crisis require coordination between local
actions, national laws, and international agreements, as well as strict enforcement of policies
(CBD, 2011; GBO3, 2010). Such a multi-jurisdictional approach is essential to prevent illegal traf-
ficking in wildlife products; enhance protection of species in public reserves; and develop effective
policies to ensure sustainable fisheries (GBO3, 2010). Management plans for individual species, as
well as for public lands and marine protected areas, will need to include adaptation to climate
change (Barnosky et al., 2011, 2012; GBO3, 2010; McLachlan and Hellmann, 2007; Solomon
et al., 2011). Assessment of species risks will need to be accelerated (IUCN, 2010), particularly for
invertebrate species (Collen et al., 2012) and fish.
In addition, it will be necessary to address the root causes of climate change and unnecessary
ecosystem transformation (see those sections of this consensus statement). An important part of the
solution will be economic valuation of natural capital and ecosystem services, such that global,
regional, and local economies account for the benefits of banking natural capital for the long run,
rather than irretrievably depleting finite species resources for short-term economic gain (Daily and
Ellison, 2002; Ehrlich et al., 2012). Workable examples already exist in China, where 120 million
farmers are being paid to farm in ways that not only yield crops and timber but also stabilize steep
slopes, control floods, and maintain biodiversity (Ehrlich et al., 2012); in Costa Rica (Daily et al.,
2000), where a national payment system for ecosystem services has helped to change deforestation
rates from among the highest in the world to among the lowest; and in New York City, where main-
taining natural landscapes for water filtration is more economical than building filtration plants
(Daily and Ellison, 2002).
Ecosystem transformation
As humans have become more abundant, we have transformed large parts of the Earth’s surface
from their pre-human ‘natural’ state into entirely different landscapes and seascapes (Vitousek
et al., 1997b). Some of these transformations have been necessary to support basic human needs;
others have been inadvertent and unanticipated.
As of 2012, somewhat more than 41% of Earth’s ice-free lands (36% of total land surface) have
been commandeered for farms, ranches, logging, cities, suburbs, roads, and other human constructs
(Foley et al., 2005, 2011; Vitousek et al., 1986) (Figure 5). This equates to an average of a little less
than 2 acres of transformed land for each person on Earth. Conversion for agriculture accounts for
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Barnosky et al. 93
most of the landscape change, with crops covering about 12% and pastureland about 26% of ice-
free land (the percentages are about 10% and 22%, respectively, for the proportion of all Earth’s
land). Urban lands account for another 3%. On top of that are vast road networks that fragment
habitats across some 50% of the entire land surface, dams that modify water flow in more than 60%
of the world’s large rivers and in many smaller ones (WWF, 2012), and continuing deforestation
that has been proceeding at the rate of about 30,000 km
2
(= 11,000 square miles) per year for the
past 16 years (FAO, 2012b). This per-year loss is roughly the equivalent of clear-cutting the entire
country of Belgium or, in the USA, the states of Massachusetts or Hawaii in one year.
Measuring the percentage of the oceans that have been transformed is much more challenging,
but it is clear that pollution, trawling, and ship traffic and noise have caused major changes along
most of the world’s coastlines (Jackson, 2008; Jackson et al., 2001). For example, bottom trawling
alone has been estimated to annually destroy an area of seabed equivalent to twice the area of the
continental USA (Hoekstra et al., 2010). Human debris, particularly plastics, also is ubiquitous in
ocean waters, even far offshore (NOAA, 2013a).
The human footprint extends even outside of the ecosystems that have been transformed whole-
sale by people. Nearly every terrestrial ecosystem in the world now integrates at least a few species
that ultimately were introduced by human activities (Ellis, 2011; Ellis et al., 2012; Vitousek et al.,
1997a), sometimes with devastating losses in ecosystem services (Pejchar and Mooney, 2009), and
invasive species now number in the hundreds in most major marine ports (Bax et al., 2003; Cohen
and Carlton, 1998) and in the thousands on most continents (DAISIE, 2012; Thuilier, 2012;
Vitousek et al., 1997a). All told, 83% of the entire land surface exhibits human impact defined as
influenced by at least one of the following factors: human population density greater than 1 person/
km
2
(= 1 person/0.4 square miles, or 247 acres); agricultural activity; built-up areas or settlements;
Figure 5. Almost half of Earth’s ice-free land has already been changed completely by human activities.
Nowhere on the land or in the sea is completely free of human influence.
Source: AD Barnosky.
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94 The Anthropocene Review 1(1)
being within 15 km (9.3 miles) of a road or coastline; or nighttime light bright enough to be
detected by satellites (Ewing et al., 2010; Sanderson et al., 2002). Adding in the effect of climate
change, every place on Earth exhibits at least some human impact, even the most remote parts of
the land and oceans (Halpern et al., 2008).
Causes for concern
There are two conflicting concerns with respect to ecosystem transformation.
The need to minimize the human footprint to prevent extinction of other species and degra-
dation of essential ecosystem services. Ecological ‘tipping points’, where whole ecosystems
change suddenly and unexpectedly to become less biodiverse and in many cases less pro-
ductive (Scheffer et al., 2009), are known to be triggered by transforming threshold percent-
ages of their areas. Many studies document that when 50% to 90% of patches within a
landscape are disturbed, the remaining undisturbed patches undergo rapid, irreversible
changes as well (Barnosky et al., 2012; Bascompte and Solé, 1996; Noss et al., 2012; Pardini
et al., 2010; Swift and Hannon, 2010). Therefore, wholesale ecological transformation of
more than half of Earth’s ecosystems by direct human impacts is prone to trigger unantici-
pated, irreversible degradation even in ecosystems that are not directly utilized by humans.
Such changes already are becoming evident in nitrogen deposition in remote arctic lakes
(Holtgrieve et al., 2011), by dwindling populations of once-common species in some nature
reserves (McMenamin et al., 2008), by millions of acres of beetle-killed forests (Kurz et al.,
2008), and by invasive species such as zebra mussels (Pejchar and Mooney, 2009; Vitousek
et al., 1997a).
The need to feed, house, and provide acceptably high standards of living for the 7 billion
people that are now on the planet plus 2.5 billion more that probably will be added over the
next three decades (PRB, 2012; UNDESA, 2011) means that the demands for land use will
accelerate (see the ‘Population growth’ section for more details on this). Nearly 70% of the
arable land that has not yet been converted to agricultural use is in tropical grasslands and
forests, which include some of the world’s most important biodiversity reservoirs and so far
are among the lands least impacted by humans (Hoekstra et al., 2010). Farming less arable
lands would take even more acres per person than at present, because of lower productivity
per acre (Ehrlich and Ehrlich, 2013).
Cities, regions, or countries that are not able to provide a high quality of life on a low [Ecological]
Footprint will be at a disadvantage in a resource-constrained future. (Ewing et al., 2010)
Solutions
Because food production is the chief transformer of natural ecosystems, a key challenge will be
feeding more people without significantly adding to the existing agricultural and fisheries foot-
print. Valuing natural capital (as explained above in the ‘Extinctions’ section) is a promising
approach that can lead to significant gains in both biodiversity and crop yields; for instance, as has
been shown by integrating coffee farms with natural landscapes in Costa Rica (Ricketts et al.,
2004). Slowing and ultimately stopping the encroachment of agriculture into currently unculti-
vated areas (especially the few remaining tropical rainforests and savannahs) will probably require
regulatory policies and incentives for conservation. Recent studies indicate that even without
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Barnosky et al. 95
Figure 6. The brown haze of air pollution is pernicious in and around many cities, and causes at up to 6
million deaths each year. Pictured is the smog accumulating south of San Francisco, California, on a cool
winter day.
Source: EA Hadly.
increasing the agricultural footprint, it is feasible to increase food production adequately in an
environmentally sound way through (Ausubel et al., 2012; Foley et al., 2011): (a) improving yields
in the world’s currently less productive farmlands; (b) more efficiently using the water, energy, and
fertilizer necessary to increase yields; (c) eating less meat; and (d) reducing food waste through
better infrastructure, distribution, and more efficient consumption patterns – some 30% of the food
currently produced is discarded or spoiled. Adapting crop strains to changing climate will also be
required to maximize yields (Lobell et al., 2008; Walthall et al., 2012). In the oceans, solutions lie
in enhanced fisheries management; sustainable aquaculture that focuses on species for which farm-
ing does not consume more protein than is produced; and reduction of pollution, especially along
coasts (Naylor et al., 2000, 2009).
It will be necessary to avoid losing more land to suburban sprawl through emphasizing develop-
ment plans that provide higher-density housing and more efficient infrastructure in existing built-
up areas, rather than carving new communities wholesale out of less disturbed surrounding lands.
Climate change will affect all places on the planet – those that are currently little impacted by
humanity, as well as those now intensively used for agriculture or cities and towns – and the effects
will be more pronounced with greater amounts of warming. Avoiding global ecosystem transfor-
mation will therefore also require keeping climate change to a minimum.
Pollution
There are few, if any places on Earth where human-produced environmental contaminants are not
being deposited. Traces of pesticides and industrial pollutants are routinely found in samples of soil
or tree bark from virtually any forest in the world, in the blubber of whales, in polar bear body tis-
sues, in fish from most rivers and oceans, and in the umbilical cords of newborn babies (Dodds,
2008; Hoekstra et al., 2010). Smog in many cities is far above levels considered safe (WHO, 2011)
(Figure 6). In the worst cases – such as in Beijing during January 2013 – polluted air can be seen
from space. Other air pollutants, such as greenhouse gases and ozone, are invisible but cause seri-
ous global-scale problems, notably climate disruption. Oil spills routinely contaminate oceans and
coastlines, as well as inland waters and land areas. Nuclear waste, and especially radioactive con-
tamination from accidents at nuclear plants, is a growing problem, as is the ubiquity of hormone-
disrupting or cancer-causing chemicals such as bisphenol-A (commonly known as BPA) (Guillette
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96 The Anthropocene Review 1(1)
and Iguchi, 2012). Activities such as mining, manufacturing, and recycling of electronic equipment
have not only concentrated dangerous pollutants locally, but also distributed them worldwide,
notably harmful substances such as lead, chromium, mercury, and asbestos (Qiu, 2013; Staff,
Blacksmith Institute, 2012).
Causes for concern
Health impacts. The health costs of pollution are enormous. At least 125 million people
are now at direct risk from toxic wastes produced by mining and manufacturing (Staff,
Blacksmith Institute, 2012). As of 2010 air pollution caused up to 6 million premature
deaths per year (Lim et al., 2012; WHO, 2011). Environmental exposures are thought to
contribute to 19% of cancer incidence worldwide (Staff, Blacksmith Institute, 2012).
Millions of people drink groundwater contaminated with cancer-causing arsenic or
harmful microbes (Fendorf et al., 2010). All total, as of 2010, the number of years lost
through illness, disability or early death (disability-adjusted life years, or DALYS) from
environmental hazards is probably greater than those lost to malaria, tuberculosis, and
HIV/AIDS combined (Lim et al., 2012). An emerging concern is the effect of hormone-
simulating chemicals, such as endocrine disruptors, which may be affecting human
growth, development, and health on a large scale. For instance, endocrine disruptors
have been linked to earlier onset of puberty and obesity (Guillette and Iguchi, 2012). The
latter also leads to increased incidence of heart disease and type II diabetes (Newbold
et al., 2009).
Dead zones. Excess nitrogen from farm fertilizers, sewage plants, livestock pens, and coal
plants eventually ends up in waterways and makes its way to the oceans, where it stimulates
prodigious algal growth. Decay of the dead algae then sucks all the oxygen out of the water
(Dodds, 2008; Hoekstra et al., 2010). The result is a dead zone where marine life is greatly
reduced. Most coasts of the world now exhibit elevated nitrogen flow, with large dead zones
occurring near major population centers (Diaz and Rosenberg, 2008; NASA, 2010) (Figure
7).
Environmental devastation. Greenhouse gas pollutants – primarily human-produced carbon
dioxide (CO
2
), nitrous oxide (NO), and methane (CH
4
) – are the causes of one of the biggest
environmental problems, climate disruption (IPCC, 2007). Herbicides, pesticides, and vari-
ous chemicals used in plastic production contaminate many waterways directly, and then are
taken up by organisms and bioamplified through food chains. Virtually all human beings on
Earth carry a burden of these persistent chemicals, many of which are endocrine disruptors.
Pharmaceuticals meant for humans or livestock, and subsequently flushed into drains or
otherwise finding their way into rivers and lakes, disrupt growth and development of
amphibians and fish. Sewage and excess fertilizer contribute significantly to damaging
more than half of the world’s coral reefs, and in some ecoregions, up to 90% of reefs (Dodds,
2008; Hoekstra et al., 2010).
Solutions
The pollution problem is not a new one. The sources of environmental contamination generally are
well known, especially for the worst sources, such as lead-battery recycling, lead smelting, mining
and ore processing, tannery operations, municipal and industrial dumpsites, product manufacturing,
chemical manufacturing, petrochemical industry, electronic waste, agricultural pesticides and excess
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Barnosky et al. 97
fertilizers, and greenhouse gases (Dodds, 2008; Hoekstra et al., 2010; Staff, Blacksmith Institute,
2012). Viable prevention and cleanup solutions are available for most pollutants, but are often not
employed because of cost. Significant reductions in pollution from manufacturing can be found in
better regulation and oversight of industries using and producing hazardous wastes; better industry
practices in controlling hazardous wastes and substances; educating local communities and hazard-
ous industries in adverse effects of pollutants; enhancement of technology for management and
treatment of pollutants; and minimizing location of potentially hazardous industries near population
centers. Reducing air pollution (including greenhouse gases) requires phasing out coal-fired power
plants and high-emissions vehicles immediately, and over time replacing fossil-fuel sources of
energy with clean energy. Minimizing agricultural pollution requires maximizing efficiency in
application of fertilizers, pesticides, and antibiotics.
Even more promising than these traditional approaches is to use our current scientific under-
standing of the mechanisms of toxicity to guide synthetic chemistry toward a new generation of
inherently safer materials. This is now eminently feasible, and it promises to reward entrepreneurs
who adopt these green chemistry approaches in the market (Schug et al., 2013).
Population growth and resource consumption
There are two aspects to the population problem. One is how many people are on Earth (Figure 8).
The other is the wide disparity in the ‘ecological footprint’ among different countries and societal
Figure 7. World distribution of dead zones in the ocean caused primarily by nitrogen pollution.
Source: NASA (2010).
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98 The Anthropocene Review 1(1)
sectors, with a relatively small proportion of humanity inefficiently using and impacting an inordi-
nately large proportion of ecological resources (Figure 9).
Today there are more than 7 billion people on the planet. Demographic projections of popula-
tion growth indicate that some 2.5 billion more people may be added to the world population by
2050 (PRB, 2012; UNDESA, 2011), when today’s children will be reaching middle age (see the
population growth chart, Figure 8). How population actually changes in coming decades depends
largely on what happens to fertility rates (the average number of children born per woman in the
population in her lifetime), as well as mortality rates. If the global average fertility rate stayed at its
present level, there could be 27 billion people on Earth in the year 2100, but that is extremely
unlikely. If fertility changed worldwide to ‘replacement rate’ (in which parents just ‘replaced’
themselves in the next generation – about 2.1 children per woman) and mortality rates were those
typical of developed countries, then there would be 10.1 billion people in 2100. With a global aver-
age fertility rate of ½ child above replacement rate, the population would reach 15.8 billion in
2100, and a rate of ½ child below replacement would lead to an early peak in population size and
a decline to about 6.2 billion people by 2100.
There are very wide differences in fertility between countries today. At the low end, rates are
just 1.2 or 1.3 in several developed countries, including Latvia, Portugal, South Korea, and
Singapore. Some countries with slightly higher fertility rates now show declining rates, including
Russia, Germany, and Japan. Virtually all developed countries and a number of developing coun-
tries, including China, Brazil, and Thailand, now have below-replacement fertility, and their popu-
lations are on track to stop growing within a few decades at most. By contrast, many very poor
developing countries still have fertility rates as high as six or more children per family: e.g. Zambia,
Somalia, Burundi, and Afghanistan, among others. It is the high fertility in these regions that may
keep the world population growing for a century more unless population policies lower their fertil-
ity sooner rather than later.
Figure 8. If the fertility rate in all countries rapidly changes so each family on average has one daughter,
population will crest by 2050, then stabilize around 10.1 billion.
Source: Data from UNDESA (2011).
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Barnosky et al. 99
Figure 9. Consumption varies dramatically among countries, as illustrated by this graph of average
barrels of oil used per person per year in some of the top oil-consuming countries compared with other
representative nations. Numbers in parentheses give world rank in oil consumption. Numbers at right
are barrels used per person per year. The challenge is bringing down per-capita consumption rates in
countries in which rates are now too high, while allowing for growth in developing countries that are
now at low consumption rates. In the case of fossil fuels, scaling up of renewables and new technological
innovations will be required to solve the problem.
Source: Data from Central Intelligence Agency (CIA), 2013: ref. 115.
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100 The Anthropocene Review 1(1)
Causes for concern
Each of the 7 billion people now on Earth contributes at some level to climate disruption, extinc-
tions, ecosystem transformation, and pollution. The actual contributions of course vary from region
to region, country to country, and between rich and poor (Figure 9), with the general pattern being
a much larger per capita footprint in highly industrialized, wealthier countries, and a lower per
capita footprint in developing, poorer countries. Although each individual contribution to the
global-change footprint can be tiny, when multiplied by billions, the effect becomes inordinately
large. Among the key ways population growth contributes to world problems are the following.
Climate disruption. On average each person on Earth produces about 4.9 tonnes of CO
2
per
year, as of 2011 (Olivier et al., 2012); thus, as population grows, greenhouse gases and con-
sequent climate disruption increase proportionately.
Extinctions. Direct causes of extinction (habitat destruction, overexploitation) can be
expected to increase as billions more people occupy and use more and more of the planet
(Hoekstra et al., 2010). Further extinctions are likely to result from climate change. In addi-
tion, there are serious indirect impacts, notably the amount of net primary productivity, or
NPP, that humans consume or co-opt. (NPP is a measure of the ‘natural energy’ available to
power the global ecosystem. It is technically defined as the net amount of solar energy con-
verted to plant organic matter through photosynthesis.) Humans now appropriate about 28%
of all NPP (although estimates range from 23% to 40%) (Haberl et al., 2007; Running, 2012;
Smith et al., 2012; Vitousek et al., 1986, 1997b). There are limits to the amount of NPP that
can be produced on Earth, so the more NPP that humans use, the less is available for other
species. That means that as the human population grows, populations of other species inevi-
tably go extinct (unless special conservation measures mitigate the losses) because of global
energy constraints. Calculations that assume no change in human consumption patterns
indicate that the amount of NPP required by 20 billion people – which would occur by the
year 2085 if fertility rates stayed the same as they are now – would cause the extinction of
most other species on Earth (Maurer, 1996). Clearly, a human population of that size is
untenable.
Ecosystem transformation. A little less than 2 acres of land has already been converted for
each person on Earth (Barnosky et al., 2012; Foley et al., 2011; Vitousek et al., 1997b). If
that per capita rate of land conversion continued, adding 2.5 billion more people to the
planet means that the majority of Earth’s lands – a little over 50% – would have been
changed into farms, pastures, cities, towns, and roads by 2050. Continuing to use land at the
rate of 2 acres per person would mean that 85% of Earth’s lands would have to be used –
including inhospitable places such as deserts, the Arctic, and the Antarctic – if the popula-
tion hit 15 billion. Such unworkable scenarios underscore that population cannot grow
substantially without reducing the human footprint.
Pollution. All of the most dangerous sources of pollution result from per capita demand for
goods and services and, given current practices, will increase proportionately with the num-
ber of people on Earth. Additionally, there is the problem of treating and disposing of human
waste (sewage and garbage), which multiplies roughly in proportion to numbers of people.
An important consideration is that basic needs – a place to live, food, water, and adequate
healthcare – are difficult to provide even for the 7 billion people already alive today. Although
international programs have been making significant gains in bringing these basic needs to more
people and places, about 80% of the world’s population still lives below poverty level (i.e. on less
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Barnosky et al. 101
than US$10 per day; 1.4 billion people still live on less than US$1.25 per day) (Shah, 2013); 2.6
billion people lack basic sanitation services (more than one-third of all the people on the planet)
(Shah, 2013); 1.1 billion people have inadequate access to water (Shah, 2013); about 870 million
people (1 in 8) lack enough food (FAO, 2012a); and 1 billion people lack access to basic healthcare
systems (Shah, 2011). Addition of 2.5 billion more people by 2050, and more after that, would
make these already-challenging problems even more difficult to solve, particularly since the high-
est fertility rates currently are in the poorest countries. For example, despite an overall decrease in
malnourished children from 1990 to 2011, the number of underfed children in Africa – where
populations have grown substantially and most countries are relatively poor – rose from about 46
million to 56 million in those two decades (WHO, 2013b).
Solutions
Two strategies will be required to avoid the worst impacts of population growth. The first involves
recognizing that sustaining at least the quality of life that exists today while still adding some bil-
lions of people will require reducing the per capita human footprint – for example, developing and
implementing carbon-neutral energy technologies, producing food and goods more efficiently,
consuming less, and wasting less. This amounts to a dual challenge of reducing the per capita use
of resources in economically developed countries, while still allowing growth in quality of life in
developing countries. For example, the average US citizen used about 22 barrels of oil per year in
2011, whereas the average person in China and India used only about 3 and 1 barrels, respectively
(Figure 9) (CIA, 2013). Evening out such disparities while still preserving quality of life will
require a transformation of energy and resource-consumption regimes in both rich and poor nations,
as well as major technological breakthroughs in some areas. Especially in the energy sector, policy
changes will be needed to ensure that developing countries can ‘leap-frog’ over outdated technolo-
gies, as occurred with the mobile phone industry. Overall, per capita consumption can be reduced
by using state-of-the-art science for designing, developing, and commercializing the materials that
are used by billions of people.
The second strategy involves ensuring that the lower population-growth projections are the ones
that prevail (Brown et al., 2011; Ehrlich et al., 2012). The medium-fertility variant worldwide (on
average one daughter per family) would stabilize world population at about 10 billion; that would
actually entail a large increase in fertility in all developed countries plus China and dozens of other
developing countries. Therefore the 10-billion benchmark clearly can be improved upon. Today,
about 40% of the population lives in countries where fertility is already near replacement, and
another 42% lives in countries where the fertility rate is significantly lower. The ‘low’ projection
(Figure 8) is achievable and should be the goal. Ending world population growth at about 8 billion
requires bringing down fertility rates in the 18% of the population (UNDESA, 2011) that live
mostly in economically disadvantaged countries, where people still lack ready access to education
and healthcare. Raising levels of education, particularly among women, and providing access to
safe and effective means of contraception to those who want it, have been proven to reduce fertility
rates substantially (Ehrlich et al., 2012; Speidel et al., 2009).
Interactions
While climate disruption, extinctions, ecosystem transformation, pollution, and population growth
all are serious problems on their own, they interact with each other in ways that make their total
effects much more than simply the sum of their parts. For example, pollution leads to local losses
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102 The Anthropocene Review 1(1)
of biodiversity, which in turn leads to major ecological changes. Cutting down old-growth rainfor-
ests permanently transforms local climate by making it effectively drier, which in turn permanently
changes the local ecosystem from forest to grassland. At the same time global climate disruption is
magnified as a result of removing a major source of carbon sequestration. Scaling up, as global
climate reaches critical thresholds of change, rapid disappearance of whole biomes, such as boreal
forests (Scheffer et al., 2012), may result. Some pressures are tied intimately to others: for instance,
increasing human population size, and especially increasing per capita consumption, multiplies the
impacts of all four of the other problems.
Causes for concern
Interaction effects markedly increase the chances that crossing critical thresholds will lead to irre-
versible change (Peters et al., 2009; Scheffer et al., 2009) (Figure 10). That means that multiple
global pressures can combine to cause undesirable changes to occur more unexpectedly, faster and
more intensely than what would be predicted from considering each pressure separately (Folke
et al., 2011; Lenton, 2011; Rockström et al., 2009; Steffen et al., 2011; Wang et al., 2012). Such
unanticipated changes in essential resources – food, water, climate predictability, biodiversity – are
likely to result in social strife.
The pressures of each dangerous trend on its own, combined with the multiplying effect of
combining them, makes it highly plausible that disruptive societal changes would occur within
decades if business as usual continues (Barnosky et al., 2012; Rockström et al., 2009; Steffen et al.,
2011). Even taken individually, the current trajectories of climate change, extinctions, ecosystem
transformation, pollution, and population growth are faster and greater than the planetary pressures
that triggered so-called ‘planetary state-changes’ in the past (Barnosky et al., 2012). Essentially,
those were times when the Earth system hit a ‘tipping point’, that is, suddenly switched to a new
condition that precipitated abrupt, major, and permanent changes, including losses of species and
shifts in ecological structure and ecosystem services that affected all places on the planet. The last
time this happened was nearly 12,000 years ago, when the last glaciation ended. In general,
Figure 10. The interactions between climate disruption, population growth and consumption, ecosystem
transformation, pollution, and extinction greatly magnify the potential for undesirable global change.
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Barnosky et al. 103
‘tipping points’ are characteristic of how biological systems respond to continued pressures, and
they are well documented at a variety of spatial and temporal scales (Scheffer et al., 2001, 2009).
Solutions
Minimizing the chances that unanticipated global changes will result from interaction effects
requires flattening the trajectories of all five dangerous trends. An important part of the solution
lies in relieving the global pressures that have the strongest interaction effects, namely popula-
tion growth, per capita resource consumption, and greenhouse gas emissions. These affect con-
ditions in all parts of the planet, because the extent of ecosystem transformation, extinctions, and
pollution inevitably multiply as population grows, as people consume more, and as climate
changes, and climate disruption becomes more pronounced as more people use energy derived
from fossil fuels.
While the science is clear that continuing the negative trends of climate disruption, extinction,
ecosystem loss, pollution, population growth and growing per capita consumption are harmful to
humanity, actually solving these problems will require recognition of their urgency by people and
governments at all levels. The technological expertise is available to mitigate many of the harmful
impacts, but ultimately, science and technology only provide the tools; it is up to society to decide
whether or not they want to use them. Therefore, a crucial next step in diffusing these problems is
societal recognition of their urgency and willingness to commit human ingenuity and resources
towards implementing solutions (Ehrlich and Ehrlich, 2013). This will entail enhanced education
about these issues at all levels, including schools, businesses, the media, and governments, and
sustainable development goals that acknowledge that human wellbeing depends on planetary well-
being (Griggs et al., 2013).
The window of time for this global effort to begin is short, because the science also demon-
strates that with each passing year of business as usual, the problems not only become worse, they
become more expensive and difficult to solve, and our chances of avoiding the worst outcomes
diminish. Put another way, starting now means we have a good chance of success; delaying even a
decade may be too late.
Funding
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit
sectors.
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... The environmental translation of these socio-economic drivers includes the correspondingly accelerated rate of greenhouse emissions (carbon dioxide, methane and nitrous oxide), leading to climate disruption on land and in oceans. Such climatic disruption encompasses global warming, with dramatic snow-and ice-thawing from polar and high-elevation lands and consequent global sea-level rise, ocean acidification and increased frequency and intensity of extreme weather events (see [14,17]). Despite the active disinformation efforts of deniers (often sponsored by big corporations and special interest groups, in particular the fossil fuel industry; see https://www.climaterealityproject.org/blog/ climate-denial-machine-how-fossil-fuel-industry-blocks-climateaction), climate change-related calamities do manage to make their way into mainstream media, including movies and documentaries. ...
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