11-09-2017, 07:29 PM
The Scientific Consensus on Climate Change
Naomi Oreskes
2004
Policy-makers and the media, particularly in the United States, frequently assert that climate science
is highly uncertain. Some have used this as an argument against adopting strong measures to reduce
greenhouse gas emissions. For example, while discussing a major U.S. Environmental Protection
Agency report on the risks of climate change, then-EPA administrator Christine Whitman argued, "As
[the report] went through review, there was less consensus on the science and conclusions on climate
change."1 Some corporations whose revenues might be adversely affected by controls on carbon
dioxide emissions have also alleged major uncertainties in the science.2 Such statements suggest that
there might be substantive disagreement in the scientific community about the reality of anthropogenic
climate change. This is not the case.
The scientific consensus is clearly expressed in the reports of the Intergovernmental Panel on
Climate Change (IPCC). Created in 1988 by the World Meteorological Organization and the United
Nations Environmental Programme, IPCC's purpose is to evaluate the state of climate science as a
basis for informed policy action, primarily on the basis of peer-reviewed and published scientific
literature.3 In its most recent assessment, IPCC states unequivocally that the consensus of scientific
opinion is that Earth's climate is being affected by human activities: "Human activities … are
modifying the concentration of atmospheric constituents … that absorb or scatter radiant energy….
[M]ost of the observed warming over the last 50 years is likely to have been due to the increase in
greenhouse gas concentrations."4
IPCC is not alone in its conclusions. In recent years, all major scientific bodies in the United States
whose members' expertise bears directly on the matter have issued similar statements. For example,
the National Academy of Sciences report, Climate Change Science: An Analysis of Some Key
Questions, begins: "Greenhouse gases are accumulating in Earth's atmosphere as a result of human
activities, causing surface air temperatures and subsurface ocean temperatures to rise."5 The report
explicitly asks whether the IPCC assessment is a fair summary of professional scientific thinking, and
answers yes: "The IPCC's conclusion that most of the observed warming of the last 50 years is likely
to have been due to the increase in greenhouse gas concentrations accurately reflects the current
thinking of the scientific community on this issue."6
Others agree. The American Meteorological Society,7 the American Geophysical Union,8 and the
American Association for the Advancement of Science (AAAS) all have issued statements in recent
years concluding that the evidence for human modification of climate is compelling.9
The drafting of such reports and statements involves many opportunities for comment, criticism,
and revision, and it is not likely that they would diverge greatly from the opinions of the societies'
members. Nevertheless, they might downplay legitimate dissenting opinions. That hypothesis was
tested by analyzing 928 abstracts, published in refereed scientific journals between 1993 and 2003,
and listed in the ISI database with the keywords "climate change."10
The 928 papers were divided into six categories: explicit endorsement of the consensus position,
evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the
consensus position. Of all the papers, 75% fell into the first three categories, either explicitly or
implicitly accepting the consensus view; 25% dealt with methods or paleoclimate, taking no position
on current anthropogenic climate change. Remarkably, none of the papers disagreed with the
consensus position.
Admittedly, authors evaluating impacts, developing methods, or studying paleoclimatic change
might believe that current climate change is natural. However, none of these papers argued that point.
This analysis shows that scientists publishing in the peer-reviewed literature agree with IPCC, the
National Academy of Sciences, and the public statements of their professional societies. Politicians,
economists, journalists, and others may have the impression of confusion, disagreement, or discord
among climate scientists, but that impression is incorrect.
The scientific consensus might, of course, be wrong. If the history of science teaches anything, it is
humility, and no one can be faulted for failing to act on what is not known. But our grandchildren will
surely blame us if they find that we understood the reality of anthropogenic climate change and failed
to do anything about it.
Many details about climate interactions are not well understood, and there are ample grounds for
continued research to provide a better basis for understanding climate dynamics. The question of
what to do about climate change is also still open. But there is a scientific consensus on the reality of
anthropogenic climate change. Climate scientists have repeatedly tried to make this clear. It is time
for the rest of us to listen.
Naomi Oreskes
2004
Policy-makers and the media, particularly in the United States, frequently assert that climate science
is highly uncertain. Some have used this as an argument against adopting strong measures to reduce
greenhouse gas emissions. For example, while discussing a major U.S. Environmental Protection
Agency report on the risks of climate change, then-EPA administrator Christine Whitman argued, "As
[the report] went through review, there was less consensus on the science and conclusions on climate
change."1 Some corporations whose revenues might be adversely affected by controls on carbon
dioxide emissions have also alleged major uncertainties in the science.2 Such statements suggest that
there might be substantive disagreement in the scientific community about the reality of anthropogenic
climate change. This is not the case.
The scientific consensus is clearly expressed in the reports of the Intergovernmental Panel on
Climate Change (IPCC). Created in 1988 by the World Meteorological Organization and the United
Nations Environmental Programme, IPCC's purpose is to evaluate the state of climate science as a
basis for informed policy action, primarily on the basis of peer-reviewed and published scientific
literature.3 In its most recent assessment, IPCC states unequivocally that the consensus of scientific
opinion is that Earth's climate is being affected by human activities: "Human activities … are
modifying the concentration of atmospheric constituents … that absorb or scatter radiant energy….
[M]ost of the observed warming over the last 50 years is likely to have been due to the increase in
greenhouse gas concentrations."4
IPCC is not alone in its conclusions. In recent years, all major scientific bodies in the United States
whose members' expertise bears directly on the matter have issued similar statements. For example,
the National Academy of Sciences report, Climate Change Science: An Analysis of Some Key
Questions, begins: "Greenhouse gases are accumulating in Earth's atmosphere as a result of human
activities, causing surface air temperatures and subsurface ocean temperatures to rise."5 The report
explicitly asks whether the IPCC assessment is a fair summary of professional scientific thinking, and
answers yes: "The IPCC's conclusion that most of the observed warming of the last 50 years is likely
to have been due to the increase in greenhouse gas concentrations accurately reflects the current
thinking of the scientific community on this issue."6
Others agree. The American Meteorological Society,7 the American Geophysical Union,8 and the
American Association for the Advancement of Science (AAAS) all have issued statements in recent
years concluding that the evidence for human modification of climate is compelling.9
The drafting of such reports and statements involves many opportunities for comment, criticism,
and revision, and it is not likely that they would diverge greatly from the opinions of the societies'
members. Nevertheless, they might downplay legitimate dissenting opinions. That hypothesis was
tested by analyzing 928 abstracts, published in refereed scientific journals between 1993 and 2003,
and listed in the ISI database with the keywords "climate change."10
The 928 papers were divided into six categories: explicit endorsement of the consensus position,
evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the
consensus position. Of all the papers, 75% fell into the first three categories, either explicitly or
implicitly accepting the consensus view; 25% dealt with methods or paleoclimate, taking no position
on current anthropogenic climate change. Remarkably, none of the papers disagreed with the
consensus position.
Admittedly, authors evaluating impacts, developing methods, or studying paleoclimatic change
might believe that current climate change is natural. However, none of these papers argued that point.
This analysis shows that scientists publishing in the peer-reviewed literature agree with IPCC, the
National Academy of Sciences, and the public statements of their professional societies. Politicians,
economists, journalists, and others may have the impression of confusion, disagreement, or discord
among climate scientists, but that impression is incorrect.
The scientific consensus might, of course, be wrong. If the history of science teaches anything, it is
humility, and no one can be faulted for failing to act on what is not known. But our grandchildren will
surely blame us if they find that we understood the reality of anthropogenic climate change and failed
to do anything about it.
Many details about climate interactions are not well understood, and there are ample grounds for
continued research to provide a better basis for understanding climate dynamics. The question of
what to do about climate change is also still open. But there is a scientific consensus on the reality of
anthropogenic climate change. Climate scientists have repeatedly tried to make this clear. It is time
for the rest of us to listen.
"Let me issue and control a nation's money and I care not who writes the laws. - Mayer Rothschild
"Civil disobedience is not our problem. Our problem is civil obedience! People are obedient in the face of poverty, starvation, stupidity, war, and cruelty. Our problem is that grand thieves are running the country. That's our problem!" - Howard Zinn
"If there is no struggle there is no progress. Power concedes nothing without a demand. It never did and never will" - Frederick Douglass
"Civil disobedience is not our problem. Our problem is civil obedience! People are obedient in the face of poverty, starvation, stupidity, war, and cruelty. Our problem is that grand thieves are running the country. That's our problem!" - Howard Zinn
"If there is no struggle there is no progress. Power concedes nothing without a demand. It never did and never will" - Frederick Douglass