Scientists have a moral obligation to clearly warn
humanity of any catastrophic threat and to “tell it like it is.” On the
basis of this obligation and the graphical indicators presented below,
we declare, with more than 11,000 scientist signatories from around the
world, clearly and unequivocally that planet Earth is facing a climate
emergency.
Exactly 40 years ago, scientists from 50 nations met at
the First World Climate Conference (in Geneva 1979) and agreed that
alarming trends for climate change made it urgently necessary to act.
Since then, similar alarms have been made through the 1992 Rio Summit,
the 1997 Kyoto Protocol, and the 2015 Paris Agreement, as well as scores
of other global assemblies and scientists’ explicit warnings of
insufficient progress (Ripple et al.
2017).
Yet greenhouse gas (GHG) emissions are still rapidly rising, with
increasingly damaging effects on the Earth's climate. An immense
increase of scale in endeavors to conserve our biosphere is needed to
avoid untold suffering due to the climate crisis (IPCC
2018).
Most
public discussions on climate change are based on global surface
temperature only, an inadequate measure to capture the breadth of human
activities and the real dangers stemming from a warming planet (Briggs
et al.
2015).
Policymakers and the public now urgently need access to a set of
indicators that convey the effects of human activities on GHG emissions
and the consequent impacts on climate, our environment, and society.
Building on prior work (see
supplemental file S2),
we present a suite of graphical vital signs of climate change over the
last 40 years for human activities that can affect GHG emissions and
change the climate (figure
1), as well as actual climatic impacts (figure
2).
We use only relevant data sets that are clear, understandable,
systematically collected for at least the last 5 years, and updated at
least annually.
Figure 1.
Change
in global human activities from 1979 to the present. These indicators
are linked at least in part to climate change. In panel (f), annual tree
cover loss may be for any reason (e.g., wildfire, harvest within tree
plantations, or conversion of forests to agricultural land). Forest gain
is not involved in the calculation of tree cover loss. In panel (h),
hydroelectricity and nuclear energy are shown in
figure S2.
The rates shown in panels are the percentage changes per decade across
the entire range of the time series. The annual data are shown using
gray points. The black lines are local regression smooth trend lines.
Abbreviation: Gt oe per year, gigatonnes of oil equivalent per year.
Sources and additional details about each variable are provided in
supplemental file S2, including
table S2.
Figure 2.
Climatic
response time series from 1979 to the present. The rates shown in the
panels are the decadal change rates for the entire ranges of the time
series. These rates are in percentage terms, except for the interval
variables (d, f, g, h, i, k), where additive changes are reported
instead. For ocean acidity (pH), the percentage rate is based on the
change in hydrogen ion activity, a
H+ (where lower pH values
represent greater acidity). The annual data are shown using gray points.
The black lines are local regression smooth trend lines. Sources and
additional details about each variable are provided in
supplemental file S2, including
table S3.
The
climate crisis is closely linked to excessive consumption of the
wealthy lifestyle. The most affluent countries are mainly responsible
for the historical GHG emissions and generally have the greatest per
capita emissions (
table S1).
In the present article, we show general patterns, mostly at the global
scale, because there are many climate efforts that involve individual
regions and countries. Our vital signs are designed to be useful to the
public, policymakers, the business community, and those working to
implement the Paris climate agreement, the United Nations’ Sustainable
Development Goals, and the Aichi Biodiversity Targets.
Profoundly
troubling signs from human activities include sustained increases in
both human and ruminant livestock populations, per capita meat
production, world gross domestic product, global tree cover loss, fossil
fuel consumption, the number of air passengers carried, carbon dioxide
(CO
2) emissions, and per capita CO
2 emissions since 2000 (figure
1,
supplemental file S2). Encouraging signs include decreases in global fertility (birth) rates (figure
1b), decelerated forest loss in the Brazilian Amazon (figure
1g), increases in the consumption of solar and wind power (figure
1h), institutional fossil fuel divestment of more than US$7 trillion (figure
1j), and the proportion of GHG emissions covered by carbon pricing (figure
1m). However, the decline in human fertility rates has substantially slowed during the last 20 years (figure
1b), and the pace of forest loss in Brazil's Amazon has now started to increase again (figure
1g).
Consumption of solar and wind energy has increased 373% per decade, but
in 2018, it was still 28 times smaller than fossil fuel consumption
(combined gas, coal, oil; figure
1h). As of 2018, approximately 14.0% of global GHG emissions were covered by carbon pricing (figure
1m), but the global emissions-weighted average price per tonne of carbon dioxide was only around US$15.25 (figure
1n). A much higher carbon fee price is needed (IPCC
2018,
section 2.5.2.1). Annual fossil fuel subsidies to energy companies have
been fluctuating, and because of a recent spike, they were greater than
US$400 billion in 2018 (figure
1o).
Especially disturbing are concurrent trends in the vital signs of climatic impacts (figure
2,
supplemental file S2). Three abundant atmospheric GHGs (CO
2, methane, and nitrous oxide) continue to increase (see
figure S1 for ominous 2019 spike in CO
2), as does global surface temperature (figure
2a–2d).
Globally, ice has been rapidly disappearing, evidenced by declining
trends in minimum summer Arctic sea ice, Greenland and Antarctic ice
sheets, and glacier thickness worldwide (figure
2e–2h).
Ocean heat content, ocean acidity, sea level, area burned in the United
States, and extreme weather and associated damage costs have all been
trending upward (figure
2i–2n).
Climate change is predicted to greatly affect marine, freshwater, and
terrestrial life, from plankton and corals to fishes and forests (IPCC
2018,
2019). These issues highlight the urgent need for action.
Despite
40 years of global climate negotiations, with few exceptions, we have
generally conducted business as usual and have largely failed to address
this predicament (figure
1). The climate crisis has arrived and is accelerating faster than most scientists expected (figure
2, IPCC
2018). It is more severe than anticipated, threatening natural ecosystems and the fate of humanity (IPCC
2019).
Especially worrisome are potential irreversible climate tipping points
and nature's reinforcing feedbacks (atmospheric, marine, and
terrestrial) that could lead to a catastrophic “hothouse Earth,” well
beyond the control of humans (Steffen et al.
2018).
These climate chain reactions could cause significant disruptions to
ecosystems, society, and economies, potentially making large areas of
Earth uninhabitable.
To secure a sustainable future, we must
change how we live, in ways that improve the vital signs summarized by
our graphs. Economic and population growth are among the most important
drivers of increases in CO
2 emissions from fossil fuel combustion (Pachauri et al.
2014, Bongaarts and O’Neill
2018);
therefore, we need bold and drastic transformations regarding economic
and population policies. We suggest six critical and interrelated steps
(in no particular order) that governments, businesses, and the rest of
humanity can take to lessen the worst effects of climate change. These
are important steps but are not the only actions needed or possible
(Pachauri et al.
2014, IPCC
2018,
2019).
Energy
The world must quickly implement massive energy efficiency and
conservation practices and must replace fossil fuels with low-carbon
renewables (figure
1h) and other cleaner sources of energy if safe for people and the environment (
figure S2). We should leave remaining stocks of fossil fuels in the ground (see the timelines in IPCC
2018)
and should carefully pursue effective negative emissions using
technology such as carbon extraction from the source and capture from
the air and especially by enhancing natural systems (see “Nature”
section). Wealthier countries need to support poorer nations in
transitioning away from fossil fuels. We must swiftly eliminate
subsidies for fossil fuels (figure
1o) and use effective and fair policies for steadily escalating carbon prices to restrain their use.
Short-lived pollutants
We need to promptly reduce the emissions of short-lived climate pollutants, including methane (figure
2b),
black carbon (soot), and hydrofluorocarbons (HFCs). Doing this could
slow climate feedback loops and potentially reduce the short-term
warming trend by more than 50% over the next few decades while saving
millions of lives and increasing crop yields due to reduced air
pollution (Shindell et al.
2017). The 2016 Kigali amendment to phase down HFCs is welcomed.
Nature
We must protect and restore Earth's ecosystems. Phytoplankton, coral
reefs, forests, savannas, grasslands, wetlands, peatlands, soils,
mangroves, and sea grasses contribute greatly to sequestration of
atmospheric CO
2. Marine and terrestrial plants, animals, and
microorganisms play significant roles in carbon and nutrient cycling and
storage. We need to quickly curtail habitat and biodiversity loss
(figure
1f–1g),
protecting the remaining primary and intact forests, especially those
with high carbon stores and other forests with the capacity to rapidly
sequester carbon (proforestation), while increasing reforestation and
afforestation where appropriate at enormous scales. Although available
land may be limiting in places, up to a third of emissions reductions
needed by 2030 for the Paris agreement (less than 2°C) could be obtained
with these natural climate solutions (Griscom et al.
2017).
Food
Eating mostly plant-based foods while reducing the global consumption of animal products (figure
1c–d), especially ruminant livestock (Ripple et al.
2014),
can improve human health and significantly lower GHG emissions
(including methane in the “Short-lived pollutants” step). Moreover, this
will free up croplands for growing much-needed human plant food instead
of livestock feed, while releasing some grazing land to support natural
climate solutions (see “Nature” section). Cropping practices such as
minimum tillage that increase soil carbon are vitally important. We need
to drastically reduce the enormous amount of food waste around the
world.
Economy
Excessive extraction of materials and overexploitation of ecosystems,
driven by economic growth, must be quickly curtailed to maintain
long-term sustainability of the biosphere. We need a carbon-free economy
that explicitly addresses human dependence on the biosphere and
policies that guide economic decisions accordingly. Our goals need to
shift from GDP growth and the pursuit of affluence toward sustaining
ecosystems and improving human well-being by prioritizing basic needs
and reducing inequality.
Population
Still increasing by roughly 80 million people per year, or more than 200,000 per day (figure
1a–b),
the world population must be stabilized—and, ideally, gradually
reduced—within a framework that ensures social integrity. There are
proven and effective policies that strengthen human rights while
lowering fertility rates and lessening the impacts of population growth
on GHG emissions and biodiversity loss. These policies make
family-planning services available to all people, remove barriers to
their access and achieve full gender equity, including primary and
secondary education as a global norm for all, especially girls and young
women (Bongaarts and O’Neill
2018).
Contributing reviewers
Franz Baumann, Ferdinando Boero, Doug Boucher, Stephen Briggs, Peter
Carter, Rick Cavicchioli, Milton Cole, Eileen Crist, Dominick A.
DellaSala, Paul Ehrlich, Iñaki Garcia-De-Cortazar, Daniel Gilfillan,
Alison Green, Tom Green, Jillian Gregg, Paul Grogan, John Guillebaud,
John Harte, Nick Houtman, Charles Kennel, Christopher Martius, Frederico
Mestre, Jennie Miller, David Pengelley, Chris Rapley, Klaus Rohde, Phil
Sollins, Sabrina Speich, David Victor, Henrik Wahren, and Roger
Worthington.
Funding
The Worthy Garden Club furnished partial funding for this project.
Project website
To view the Alliance of World Scientists website or to sign this article, go to
https://scientistswarning.forestry.oregonstate.edu.
Supplemental material
A list of the signatories appears in supplemental file S1.
Author Biographical
William J. Ripple (
bill.ripple@oregonstate.edu) and Christopher Wolf (
christopher.wolf@oregonstate.edu)
are affiliated with the Department of Forest Ecosystems and Society at
Oregon State University, in Corvallis and contributed equally to the
work. Thomas M. Newsome is affiliated with the School of Life and
Environmental Sciences at The University of Sydney, in Sydney, New South
Wales, Australia. Phoebe Barnard is affiliated with the Conservation
Biology Institute, in Corvallis, Oregon, and with the African Climate
and Development Initiative, at the University of Cape Town, in Cape
Town, South Africa. William R. Moomaw is affiliated with The Fletcher
School and the Global Development and Environment Institute, at Tufts
University, in Medford, Massachusetts
11,258 scientist signatories from 153 countries (list in
supplemental file S1)
References cited - Due to format issues, please refer to published work for references.
© The Author(s) 2019. Published by Oxford University Press on behalf of the American Institute of Biological Sciences.
