The "World Scientists' Warning to Humanity" was a document written in 1992 by
Henry W. Kendall and signed by about 1,700 leading scientists. Twenty-five years later, in November 2017, 15,364 scientists signed "World Scientists' Warning to Humanity: A Second Notice" written by
William J. Ripple and seven co-authors calling for, among other things,
human population planning
Human population planning is the practice of managing the growth rate of a human population. The practice, traditionally referred to as population control, had historically been implemented mainly with the goal of increasing population growth, ...
, and drastically diminishing
per capita
''Per capita'' is a Latin phrase literally meaning "by heads" or "for each head", and idiomatically used to mean "per person".
Social statistics
The term is used in a wide variety of social science, social sciences and statistical research conte ...
consumption of
fossil fuels
A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geologica ...
,
meat
Meat is animal Tissue (biology), tissue, often muscle, that is eaten as food. Humans have hunted and farmed other animals for meat since prehistory. The Neolithic Revolution allowed the domestication of vertebrates, including chickens, sheep, ...
, and other
resources
''Resource'' refers to all the materials available in our environment which are Technology, technologically accessible, Economics, economically feasible and Culture, culturally Sustainability, sustainable and help us to satisfy our needs and want ...
. The second notice has more scientist cosigners and formal supporters than any other journal article ever published.
First publication
In late 1992, the late
Henry W. Kendall, a former chair of the board of directors of the
Union of Concerned Scientists
The Union of Concerned Scientists (UCS) is a nonprofit science advocacy organization based in the United States. The UCS membership includes many private citizens in addition to professional scientists. Anne Kapuscinski, Professor of Environment ...
(UCS), wrote the first warning, "World Scientists' Warning to Humanity", which begins: "Human beings and the natural world are on a collision course." A majority of the
Nobel Prize
The Nobel Prizes ( ; ; ) are awards administered by the Nobel Foundation and granted in accordance with the principle of "for the greatest benefit to humankind". The prizes were first awarded in 1901, marking the fifth anniversary of Alfred N ...
laureates in the sciences signed the document; about 1,700 of the world's leading
scientists
A scientist is a person who researches to advance knowledge in an area of the natural sciences.
In classical antiquity, there was no real ancient analog of a modern scientist. Instead, philosophers engaged in the philosophical study of nature ...
appended their signature.
It was sometimes offered in opposition to the
Heidelberg Appeal—also signed by numerous scientists and Nobel laureates earlier in 1992—which begins by criticizing "an irrational
ideology
An ideology is a set of beliefs or values attributed to a person or group of persons, especially those held for reasons that are not purely about belief in certain knowledge, in which "practical elements are as prominent as theoretical ones". Form ...
which is opposed to scientific and
industrial progress, and impedes economic and social development." This document was often cited by those who oppose theories relating to
climate change
Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
.
In contrast, the UCS-led
petition
A petition is a request to do something, most commonly addressed to a government official or public entity. Petitions to a deity are a form of prayer called supplication.
In the colloquial sense, a petition is a document addressed to an officia ...
contains specific recommendations: "We must, for example, move away from
fossil fuels
A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geologica ...
to more benign, inexhaustible
energy
Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...
sources to cut
greenhouse gas
Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...
emissions and the
pollution
Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...
of our
air
An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
and
water
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
. ... We must stabilize population."
Second Notice
In November 2017, 15,364 scientists signed "World Scientists' Warning to Humanity: A Second Notice" written by lead author professor of ecology,
William J. Ripple of
Oregon State University
Oregon State University (OSU) is a Public university, public Land-grant university, land-grant research university in Corvallis, Oregon, United States. OSU offers more than 200 undergraduate degree programs and a variety of graduate and doctor ...
, along with 7 co-authors calling for, among other things,
limiting population growth, and drastically diminishing
per capita
''Per capita'' is a Latin phrase literally meaning "by heads" or "for each head", and idiomatically used to mean "per person".
Social statistics
The term is used in a wide variety of social science, social sciences and statistical research conte ...
consumption of
fossil fuels
A fossil fuel is a flammable carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or microplanktons), a process that occurs within geologica ...
,
meat
Meat is animal Tissue (biology), tissue, often muscle, that is eaten as food. Humans have hunted and farmed other animals for meat since prehistory. The Neolithic Revolution allowed the domestication of vertebrates, including chickens, sheep, ...
, and other
resources
''Resource'' refers to all the materials available in our environment which are Technology, technologically accessible, Economics, economically feasible and Culture, culturally Sustainability, sustainable and help us to satisfy our needs and want ...
. The second notice included 9 time-series graphs of key indicators, each correlated to a specific issue mentioned in the original 1992 warning, to show that most environmental issues are continuing to trend in the wrong direction, most with no discernible change in rate. The article included 13 specific steps humanity could take to transition to
sustainability
Sustainability is a social goal for people to co-exist on Earth over a long period of time. Definitions of this term are disputed and have varied with literature, context, and time. Sustainability usually has three dimensions (or pillars): env ...
.
The second notice has more scientist cosigners and formal supporters than any other journal article ever published. The full warning was published in ''
BioScience
''BioScience'' is a monthly peer-reviewed scientific journal that is published by Oxford University Press on behalf of the American Institute of Biological Sciences. It was established in 1964 and was preceded by the ''AIBS Bulletin'' (1951–1 ...
'' and it can still be endorsed on the Scientists Warning website.
2019 warning on climate change and 2021 and 2022 updates
In November 2019, a group of more than 11,000 scientists from 153 countries named climate change an "emergency" that would lead to "untold human suffering" if no big shifts in action take place:
The emergency declaration emphasized that
economic growth
In economics, economic growth is an increase in the quantity and quality of the economic goods and Service (economics), services that a society Production (economics), produces. It can be measured as the increase in the inflation-adjusted Outp ...
and
population growth
Population growth is the increase in the number of people in a population or dispersed group. The World population, global population has grown from 1 billion in 1800 to 8.2 billion in 2025. Actual global human population growth amounts to aroun ...
"are among the most important drivers of increases in emissions from fossil fuel combustion" and that "we need bold and drastic transformations regarding economic and population policies".
A 2021 update to the 2019 climate emergency declaration focuses on 31 planetary vital signs (including greenhouse gases and temperature, rising sea levels, energy use, ice mass, ocean heat content, Amazon rainforest loss rate, etc), and recent changes to them. Of these, 18 are reaching critical levels. The
COVID-19 lockdowns
During the early stages of the COVID-19 pandemic, a number of Non-pharmaceutical intervention (epidemiology), non-pharmaceutical interventions, particularly lockdowns (encompassing stay-at-home orders, curfews, quarantines, and similar socie ...
, which reduced transportation and consumption levels, had very little impact on mitigating or reversing these trends. The authors say only profound changes in human behavior can meet these challenges and emphasize the need to move beyond the idea that global heating is a stand alone emergency, and is one facet of the worsening environmental crisis. This necessitates the need for transformational system changes and to focus on the root cause of these crises, the vast human
overexploitation
Overexploitation, also called overharvesting or ecological overshoot, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to ...
of the earth, rather than just addressing symptom relief. They point to six areas where fundamental changes need to be made:
(1) ''energy'' — eliminating fossil fuels and shifting to renewables;
(2) ''short-lived air pollutants'' — slashing black carbon
Black carbon (BC) is the light-absorbing refractory form of Chemical_element, elemental carbon remaining after pyrolysis (e.g., charcoal) or produced by incomplete combustion (e.g., soot).
Tihomir Novakov originated the term black carbon in ...
(soot), methane, and hydrofluorocarbon
Hydrofluorocarbons (HFCs) are synthetic organic compounds that contain fluorine and hydrogen atoms, and are the most common type of organofluorine compounds. Most are gases at room temperature and pressure. They are frequently used in air condit ...
s;
(3) ''nature'' — restoring and permanently protecting Earth's ecosystems to store and accumulate carbon and restore biodiversity;
(4) ''food'' — switching to mostly plant-based diets, reducing food waste, and improving cropping practices;
(5) ''economy'' — moving from indefinite GDP growth and overconsumption by the wealthy to ecological economics
Ecological economics, bioeconomics, ecolonomy, eco-economics, or ecol-econ is both a transdisciplinary and an interdisciplinary field of academic research addressing the interdependence and coevolution of human economy, economies and natural ec ...
and a circular economy
A circular economy (also referred to as circularity or CE) is a model of resource Production (economics), production and Resource consumption, consumption in any economy that involves sharing, leasing, Reuse, reusing, repairing, refurbishing, and ...
, in which prices reflect the full environmental costs of goods and services; and
(6) ''human population'' — stabilizing and gradually reducing the population by providing voluntary family planning and supporting education and rights for all girls and young women, which has been proven to lower fertility rates.
At the 30th anniversary of the World Scientists' Warning to Humanity, a second update to the climate emergency declaration concluded that "We are now at '
code red' on planet Earth".
2022 warning on population
In October 2022, Eileen Crist, William J. Ripple,
Paul R. Ehrlich
Paul Ralph Ehrlich (born May 29, 1932) is an American biologist known for his predictions and warnings about the consequences of population growth, including famine and resource depletion. Ehrlich is the Bing Professor Emeritus of Population ...
, William E. Rees, and Christopher Wolf all contributed to the ''Scientists' warning on population'', published by ''
Science of the Total Environment
Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into twoor threemajor branches: the natural sciences, which stu ...
'' as "part of the ongoing series of scientists' warning publications," to address the negative impacts of population size and growth on the climate and
biodiversity
Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...
, which they posit "continues to be ignored, sidestepped, or denied." It calls for two actions that, if heeded, will stop
population growth
Population growth is the increase in the number of people in a population or dispersed group. The World population, global population has grown from 1 billion in 1800 to 8.2 billion in 2025. Actual global human population growth amounts to aroun ...
before the end of this century. Firstly, the authors issue a global appeal to all adults to have no more than one child as part of the transformative changes needed to mitigate both climate change and
biodiversity loss
Biodiversity loss happens when plant or animal species disappear completely from Earth (extinction) or when there is a decrease or disappearance of species in a specific area. Biodiversity loss means that there is a reduction in Biodiversity, b ...
. Secondly, the warning urges policy-makers to "implement population policies with two key female empowerment components," primarily improving education for young women and girls and providing high-quality family-planning services to all. It emphasizes that "the combination of institutional support to plan one's child-bearing choices and educational attainment, including enhanced opportunity for higher education for women, yields immediate fertility declines." It also posits that a
sustainable human population, which according to environmental analysts is "one enjoying a modest, equitable middle-class standard of living on a planet retaining its biodiversity and with climate-related adversities minimized," is between 2 and 4 billion people.
The warning also advocates for combatting
poverty
Poverty is a state or condition in which an individual lacks the financial resources and essentials for a basic standard of living. Poverty can have diverse Biophysical environmen ...
,
patriarchy
Patriarchy is a social system in which positions of authority are primarily held by men. The term ''patriarchy'' is used both in anthropology to describe a family or clan controlled by the father or eldest male or group of males, and in fem ...
and
overconsumption
Overconsumption describes a situation where consumers overuse their available goods and services to where they can't, or don't want to, replenish or reuse them. In microeconomics, this is the point where the marginal cost of a consumer is greater ...
by the affluent, and calls for a
global wealth tax to be levied primarily against "wealthy nations, industries and people who have benefitted the most from humanity's massive-scale historical and contemporary use of fossil fuels" in order to expand "clean sanitation and water availability, food sovereignty, and electrification via renewables." It stresses that poverty alleviation must include the provision of basic public services, in particular healthcare and education.
Other scientists' warnings
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See also
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Climate emergency declaration
A climate emergency declaration or ''declaring a climate emergency'' is an action taken by governments and scientists to acknowledge humanity is in a climate crisis.
The first such declaration was made by a local government ( Darebin, Melbourne ...
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Individual action on climate change
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List of open letters by academics
;Issues
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Animal–industrial complex
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List of global issues
A global issue is a matter of public concern worldwide. This list of global issues presents problems or phenomena affecting people around the world, including but not limited to widespread social issues, economic issues, and environmental iss ...
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Anthropocene
''Anthropocene'' is a term that has been used to refer to the period of time during which human impact on the environment, humanity has become a planetary force of change. It appears in scientific and social discourse, especially with respect to ...
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Climate crisis
''Climate crisis'' is a term that is used to describe global warming and climate change and their effects. This term and the term ''climate emergency'' have been used to emphasize the threat of global warming to Earth's natural environment an ...
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Defaunation
Defaunation is the global, local, or functional extinction of animal populations or species from ecological communities. The Human overpopulation, growth of the human population, combined with advances in harvesting technologies, has led to more i ...
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Effects of global warming
Effects of climate change are well documented and growing for Earth's natural environment and human societies. Changes to the climate system include an overall warming trend, changes to precipitation patterns, and more extreme weather. As ...
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Habitat loss
Habitat destruction (also termed habitat loss or habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved elsewhere, or are dead, leading to a decrease ...
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Habitat protection
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Holocene extinction
The Holocene extinction, also referred to as the Anthropocene extinction or the sixth mass extinction, is an ongoing extinction event caused exclusively by human activities during the Holocene epoch. This extinction event spans numerous families ...
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Human impact on the environment
Human impact on the environment (or anthropogenic environmental impact) refers to changes to biophysical environments and to ecosystems, biodiversity, and natural resources caused directly or indirectly by humans. Modifying the environment to ...
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Human overpopulation
Human overpopulation (or human population overshoot) is the idea that human populations may become too large to be sustainability, sustained by their environment or resources in the long term. The topic is usually discussed in the context of wor ...
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Sustainable food system
A sustainable food system is a type of food system that provides healthy diet, healthy food to people and creates sustainable environmental, economic, and social systems that surround food. Sustainable food systems start with the development of Su ...
;Groups
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Extinction Rebellion
Extinction Rebellion (abbreviated as XR) is a UK-founded global environmental movement, with the stated aim of using nonviolent civil disobedience to compel government action to avoid tipping points in the climate system, biodiversity loss, and ...
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Scientists for Future
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Scientists for Extinction Rebellion
References
Excerpts and notes
Citations
Bibliography
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External links
World Scientists Warning to Humanity(2017)
(1992)
(2001)
''ScientistsWarning.org''(2018-Present)
''ScientistsWarning.TV''(2014-Present)
Phys.org. April 8, 2019.
{{Vegetarianism
Climate change policy
Environmentalism
Political statements
1992 in the environment
Science activism
1992 documents
2017 in the environment
2017 documents