Viewpoint
8 BioScience • January 2020 / Vol. 70 No. 1 https://academic.oup.com/bioscience
World Scientists’ Warning of a Climate Emergency
WILLIAM J. RIPPLE, CHRISTOPHER WOLF, THOMAS M. NEWSOME, PHOEBE BARNARD, WILLIAM R. MOOMAW,
AND 11,258 SCIENTIST SIGNATORIES FROM 153 COUNTRIES (LIST IN SUPPLEMENTAL FILE S1)
S
cientists 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 unequiv-
ocally 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 neces-
sary 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 insuf-
ficient progress (Ripple et al. 2017). Yet
greenhouse gas (GHG) emissions are
still rapidly rising, with increasingly
damaging effects on the Earth’s cli-
mate. 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 mea-
sure to capture the breadth of human
activities and the real dangers stem-
ming 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 emis-
sions and the consequent impacts on
climate, our environment, and society.
Building on prior work (see supple-
mental file S2), we present a suite of
graphical vital signs of climate change
over the last 40 years for human activi-
ties 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.
The climate crisis is closely linked to
excessive consumption of the wealthy
lifestyle. The most affluent countries
are mainly responsible for the his-
torical 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 individ-
ual regions and countries. Our vital
signs are designed to be useful to
the public, policymakers, the busi-
ness community, and those working
to implement the Paris climate agree-
ment, the United Nations’ Sustainable
Development Goals, and the Aichi
Biodiversity Targets.
Profoundly troubling signs from
human activities include sustained
increases in both human and rumi-
nant livestock populations, per capita
meat production, world gross domes-
tic product, global tree cover loss,
fossil fuel consumption, the number
of air passengers carried, carbon diox-
ide (CO
2
) emissions, and per capita
CO
2
emissions since 2000 (figure 1,
supplemental file S2). Encouraging
signs include decreases in global fer-
tility (birth) rates (figure 1b), decel-
erated 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 tril-
lion (figure 1j), and the proportion
of GHG emissions covered by car-
bon 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 (com-
bined 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 aver-
age 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 concur-
rent trends in the vital signs of cli-
matic 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 tempera-
ture (figure 2a–2d). Globally, ice has
been rapidly disappearing, evidenced
by declining trends in minimum sum-
mer Arctic sea ice, Greenland and
Antarctic ice sheets, and glacier thick-
ness 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 for-
ests (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
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