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World Scientists' Warning to Humanity: A Second Notice



Twenty-five years ago, the Union of Concerned Scientists and more than 1700 independent scientists, including the majority of living Nobel laureates in the sciences, penned the 1992 “World Scientists’ Warning to Humanity” (see supplemental file S1). These concerned professionals called on humankind to curtail environmental destruction and cautioned that “a great change in our stewardship of the Earth and the life on it is required, if vast human misery is to be avoided.” In their manifesto, they showed that humans were on a collision course with the natural world. They expressed concern about current, impending, or potential damage on planet Earth involving ozone depletion, freshwater availability, marine life depletion, ocean dead zones, forest loss, biodiversity destruction, climate change, and continued human population growth. I am a co-signatory for the in-press Viewpoint article in the journal BioScience ( [Oxford University Press] entitled “World Scientists’ Warning to Humanity: a second notice” by Ripple et. al. (2017). The pre-print article can be read at: [ ]. If you are a scientist from any scientific discipline (e.g. ecology, medicine, economics, etc.), and are concerned about global environmental and climate trends, the authors invite you to become a co-signatory of the paper. According to the website, more than 15,364 scientists from 184 countries have already signed.
1026 BioScience December 2017 / Vol. 67 No. 12
World Scientists’ Warning to Humanity:
A Second Notice
MAHMOUD I. MAHMOUD, WILLIAM F. LAURANCE, and 15,364 scientist signatories from 184 countries
Twenty-five years ago, the Union
of Concerned Scientists and more
than 1700 independent scientists,
including the majority of living Nobel
laureates in the sciences, penned the
1992 “World Scientists’ Warning to
Humanity” (see supplemental file S1).
These concerned professionals called
on humankind to curtail environmen-
tal destruction and cautioned that
“a great change in our stewardship of
the Earth and the life on it is required,
if vast human misery is to be avoided.
In their manifesto, they showed that
humans were on a collision course
with the natural world. They expressed
concern about current, impending,
or potential damage on planet Earth
involving ozone depletion, freshwa-
ter availability, marine life depletion,
ocean dead zones, forest loss, biodiver-
sity destruction, climate change, and
continued human population growth.
They proclaimed that fundamental
changes were urgently needed to avoid
the consequences our present course
would bring.
The authors of the 1992 declara-
tion feared that humanity was pushing
Earth’s ecosystems beyond their capac-
ities to support the web of life. They
described how we are fast approach-
ing many of the limits of what the
biosphere can tolerate without
substantial and irreversible harm.
The scientists pleaded that we stabi-
lize the human population, describing
how our large numbers—swelled by
another 2 billion people since 1992,
a 35 percent increase—exert stresses
on Earth that can overwhelm other
efforts to realize a sustainable future
(Crist et al. 2017). They implored that
we cut greenhouse gas (GHG) emis-
sions and phase out fossil fuels, reduce
deforestation, and reverse the trend of
collapsing biodiversity.
On the twenty-fifth anniversary of
their call, we look back at their warn-
ing and evaluate the human response
by exploring available time-series
data. Since 1992, with the exception
of stabilizing the stratospheric ozone
layer, humanity has failed to make
sufficient progress in generally solv-
ing these foreseen environmental chal-
lenges, and alarmingly, most of them
are getting far worse (figure 1, file S1).
Especially troubling is the current
trajectory of potentially catastrophic
climate change due to rising GHGs
from burning fossil fuels (Hansen etal.
2013), deforestation (Keenan et al.
2015), and agricultural production—
particularly from farming ruminants
for meat consumption (Ripple et al.
2014). Moreover, we have unleashed
a mass extinction event, the sixth in
roughly 540 million years, wherein
many current life forms could be
annihilated or at least committed to
extinction by the end of this century.
Humanity is now being given a
second notice, as illustrated by these
alarming trends (figure 1). We are
jeopardizing our future by not reining
in our intense but geographically and
demographically uneven material
consumption and by not perceiving
continued rapid population growth as a
primary driver behind many ecological
and even societal threats (Crist et al.
2017). By failing to adequately limit
population growth, reassess the role
of an economy rooted in growth,
reduce greenhouse gases, incentivize
renewable energy, protect habitat,
restore ecosystems, curb pollution, halt
defaunation, and constrain invasive
alien species, humanity is not taking
the urgent steps needed to safeguard
our imperilled biosphere.
As most political leaders respond to
pressure, scientists, media influencers,
and lay citizens must insist that their
governments take immediate action
as a moral imperative to current and
future generations of human and other
life. With a groundswell of organized
grassroots efforts, dogged opposition
can be overcome and political leaders
compelled to do the right thing. It is
also time to re-examine and change
our individual behaviors, including
limiting our own reproduction (ideally
to replacement level at most) and
drastically diminishing our per capita
consumption of fossil fuels, meat, and
other resources.
The rapid global decline in ozone-
depleting substances shows that we
can make positive change when we
act decisively. We have also made
advancements in reducing extreme
poverty and hunger (www.worldbank.
org). Other notable progress (which
does not yet show up in the global
data sets in figure 1) include the
rapid decline in fertility rates in many
regions attributable to investments in
girls’ and women’s education (www., the promising
decline in the rate of deforestation in
some regions, and the rapid growth
in the renewable-energy sector. We
have learned much since 1992, but
the advancement of urgently needed
changes in environmental policy,
human behavior, and global inequities
is still far from sufficient.
Sustainability transitions come
about in diverse ways, and all require
civil-society pressure and evidence-
based advocacy, political leadership,
and a solid understanding of policy
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Viewpoint December 2017 / Vol. 67 No. 12 BioScience 1027
Figure 1. Trends over time for environmental issues identified in the 1992 scientists’ warning to humanity. The years
before and after the 1992 scientists’ warning are shown as gray and black lines, respectively. Panel(a) shows emissions
of halogen source gases, which deplete stratospheric ozone, assuming a constant natural emission rate of 0.11 Mt CFC-
11-equivalent per year. In panel (c), marine catch has been going down since the mid-1990s, but at the same time, fishing
effort has been going up (supplemental file S1). The vertebrate abundance index in panel(f) has been adjusted for
taxonomic and geographic bias but incorporates relatively little data from developing countries, where there are the fewest
studies; between 1970 and 2012, vertebrates declined by 58 percent, with freshwater, marine, and terrestrial populations
declining by 81, 36, and 35 percent, respectively (file S1). Five-year means are shown in panel(h). In panel(i), ruminant
livestock consist of domestic cattle, sheep, goats, and buffaloes. Note that y-axes do not start at zero, and it is important to
inspect the data range when interpreting each graph. Percentage change, since 1992, for the variables in each panel are as
follows: (a) –68.1%; (b) –26.1%; (c) –6.4%; (d) +75.3%; (e) –2.8%; (f) –28.9%; (g) +62.1%; (h) +167.6%; and (i) humans:
+35.5%, ruminant livestock: +20.5%. Additional descriptions of the variables and trends, as well as sources for figure 1,
are included in file S1.
Ruminant livestock
CO2 emissions
(Gt CO2 per year)
Temperature change
(billion individuals)
Dead zones (number
of affected regions)
Total forest
(billion ha)
Vertebrate species
abundance (% of 1970)
Ozone depletors (Mt CFC−
11−equivalent per year)
Freshwater resources
per capita (1000 m3)
Reconstructed marine
catch (Mt per year)
1960 1992 2016 1960 1992 2016 1960 1992 2016
g. h. i.
d. e. f.
a. b. c.
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1028 BioScience December 2017 / Vol. 67 No. 12
instruments, markets, and other driv-
ers. Examples of diverse and effective
steps humanity can take to transition
to sustainability include the follow-
ing (not in order of importance or
urgency): (a) prioritizing the enact-
ment of connected well-funded and
well-managed reserves for a significant
proportion of the worlds terrestrial,
marine, freshwater, and aerial habi-
tats; (b) maintaining nature’s ecosys-
tem services by halting the conversion
of forests, grasslands, and other native
habitats; (c) restoring native plant
communities at large scales, particu-
larly forest landscapes; (d) rewilding
regions with native species, especially
apex predators, to restore ecological
processes and dynamics; (e) devel-
oping and adopting adequate policy
instruments to remedy defaunation,
the poaching crisis, and the exploi-
tation and trade of threatened spe-
cies; (f) reducing food waste through
education and better infrastructure;
(g) promoting dietary shifts towards
mostly plant-based foods; (h) further
reducing fertility rates by ensuring
that women and men have access to
education and voluntary family-plan-
ning services, especially where such
resources are still lacking; (i) increas-
ing outdoor nature education for
children, as well as the overall engage-
ment of society in the appreciation
of nature; (j) divesting of monetary
investments and purchases to encour-
age positive environmental change;
(k) devising and promoting new green
technologies and massively adopting
renewable energy sources while phas-
ing out subsidies to energy production
through fossil fuels; (l) revising our
economy to reduce wealth inequality
and ensure that prices, taxation, and
incentive systems take into account
the real costs which consumption pat-
terns impose on our environment; and
(m) estimating a scientifically defen-
sible, sustainable human population
size for the long term while rallying
nations and leaders to support that
vital goal.
To prevent widespread misery
and catastrophic biodiversity
loss, humanity must practice a
more environmentally sustainable
alternative to business as usual. This
prescription was well articulated by
the world’s leading scientists 25 years
ago, but in most respects, we have not
heeded their warning. Soon it will be
too late to shift course away from our
failing trajectory, and time is running
out. We must recognize, in our day-
to-day lives and in our governing
institutions, that Earth with all its life
is our only home.
We have been overwhelmed with the
support for our article and thank the
more than 15,000 signatories from all
ends of the Earth (see supplemental
file S2 for list of signatories). As far as
we know, this is the most scientists to
ever co-sign and formally support a
published journal article. In this paper,
we have captured the environmental
trends over the last 25 years, showed
realistic concern, and suggested a few
examples of possible remedies. Now,
as an Alliance of World Scientists
( and
with the public at large, it is important
to continue this work to document chal-
lenges, as well as improved situations,
and to develop clear, trackable, and
practical solutions while communicat-
ing trends and needs to world leaders.
Working together while respecting the
diversity of people and opinions and
the need for social justice around the
world, we can make great progress for
the sake of humanity and the planet on
which we depend.
Spanish, Portuguese, and French
versions of this article can be found
in file S1.
Peter Frumhoff and Doug Boucher
of the Union of Concerned Scientists,
as well as the following individuals,
provided thoughtful discussions,
comments, or data for this paper: Stuart
Pimm, David Johns, David Pengelley,
Guillaume Chapron, Steve Montzka,
Robert Diaz, Drik Zeller, Gary
Gibson, Leslie Green, Nick Houtman,
Peter Stoel, Karen Josephson, Robin
Comforto, Terralyn Vandetta, Luke
Painter, Rodolfo Dirzo, Guy Peer, Peter
Haswell, and Robert Johnson.
Supplemental material
Supplementary data are available at
BIOSCI online including supplemental
file 1 and supplemental file 2 (full list
of all 15,364 signatories).
References cited
Crist E, Mora C, Engelman R. 2017. The interac-
tion of human population, food production,
and biodiversity protection. Science 356:
Hansen J, et al. 2013. Assessing “dangerous
climate change”: Required reduction of
carbon emissions to protect young people,
future generations and nature. PLOS ONE
8 (art. e81648).
Keenan, RJ, Reams GA, Achard F, de Freitas JV,
Grainger A, Lindquist E. 2015. Dynamics
of global forest area: Results from the FAO
Global Forest Resources Assessment 2015.
Forest Ecology and Management 352: 9–20.
Ripple WJ, Smith P, Haberl H, Montzka SA,
McAlpine C, Boucher DH. 2014. Ruminants,
climate change and climate policy. Nature
Climate Change 4: 2–5. doi:10.1038/
William J. Ripple (,
Christopher Wolf, and Thomas M. Newsome
are affiliated with the Global Trophic Cascades
Program in the Department of Forest Ecosystems
and Society at Oregon State University, in
Corvallis. TMN is also affiliated with the Centre
for Integrative Ecology at Deakin University, in
Geelong, Australia, and the School of Life and
Environmental Sciences at The University of
Sydney, Australia. Mauro Galetti is affiliated
with the Instituto de Biociências, Universidade
Estadual Paulista, Departamento de Ecologia,
in São Paulo, Brazil. Mohammed Alamgir
is affiliated with the Institute of Forestry and
Environmental Sciences at the University of
Chittagong, in Bangladesh. Eileen Crist is
affiliated with the Department of Science and
Technology in Society at Virginia Tech, in
Blacksburg. Mahmoud I. Mahmoud is affiliated
with the ICT/Geographic Information Systems
Unit of the National Oil Spill Detection and
Response Agency (NOSDRA), in Abuja, Nigeria.
William F. Laurance is affiliated with the Centre
for Tropical Environmental and Sustainability
Science and the College of Science and
Engineering at James Cook University, in Cairns,
Queensland, Australia.
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Ruminants, climate change and climate policy
  • W J Ripple
  • P Smith
  • H Haberl
  • S A Montzka
  • C Mcalpine
  • D H Boucher
Ripple WJ, Smith P, Haberl H, Montzka SA, McAlpine C, Boucher DH. 2014. Ruminants, climate change and climate policy. Nature Climate Change 4: 2-5. doi:10.1038/ nclimate2081