Science says: 97% of climate experts agree humans are causing global warming.
Science achieves a consensus when scientists stop debating. When a question is first asked—like "what would happen if we put a load more CO2 in the atmosphere?"—there may be many hypotheses about cause and effect. Over a period of time, each idea is tested and retested (the scientific method) because reputation and kudos go to those who find the right answer. Nearly all hypotheses will fall by the wayside during this testing period, because only one is going to answer the question properly, without leaving all kinds of odd dangling bits that don't quite add up. Bad theories are usually rather untidy.
Eventually, the testing period must come to an end. The focus of investigation narrows down to those avenues that continue to make sense, that still add up, and quite often a good theory will reveal additional answers, or make powerful predictions that add substance to the theory. When Russian scientist Dmitri Mendeleev constructed the periodic table of elements, not only did he fit all known elements successfully, he predicted that elements we didn't even know about would turn up later on, and they did!
So a consensus in science is different from a political one. There is no vote. Scientists give up the debate because the sheer weight of consistent evidence is too compelling, the tide too strong to swim against any longer. Scientists change their minds on the basis of the evidence, and a consensus emerges over time. Not only do scientists stop debating, they also start relying on each others' work. All science depends on that which precedes it, and when one scientist builds on the work of another, he acknowledges the work of others through citations. The work that forms the foundation of climate change science is cited with great frequency by many other scientists, demonstrating that the theory is widely accepted and relied upon.
In the field of climate studies, which is informed by many different disciplines, the consensus is demonstrated by the number of scientists who have stopped debating what is causing climate change—and that's nearly all of them. A survey of all peer-reviewed papers on the subject "global climate change" published between 1993 and 2003 shows that not a single paper rejected the consensus position that global warming is man-made. 75% of the papers agreed with the consensus position while 25% made no comment either way, focusing on methods analysis instead (Oreskes 2004).
Several subsequent studies confirm that "...the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes." (Doran 2009). In other words, more than 95% of scientists working in the disciplines contributing to studies of our climate, accept that climate change is almost certainly being caused by human activities.
We should also consider official scientific institutions and what they think about climate change. There are no national or major scientific institutions anywhere in the world that dispute the theory of anthropogenic climate change. Not one.
In the field of climate science, the consensus is unequivocal: human activities are causing climate change.
Science says: That humans are causing global warming is the position of the Academies of Science from 19 countries plus many scientific organizations that study climate science. More specifically, around 95% of active climate researchers actively publishing climate papers endorse the consensus position.
Scientists need to back up their opinions with research and data that survive the peer-review process. A survey of all peer-reviewed abstracts on the subject 'global climate change' published between 1993 and 2003 shows that not a single paper rejected the consensus position that global warming is man caused (Oreskes 2004). 75% of the papers agreed with the consensus position while 25% made no comment either way (focused on methods or paleoclimate analysis).
Subsequent research has confirmed this result. A survey of 3146 earth scientists asked the question "Do you think human activity is a significant contributing factor in changing mean global temperatures?" (Doran 2009). More than 90% of participants had Ph.D.s, and 7% had master's degrees. Overall, 82% of the scientists answered yes. However, what are most interesting are responses compared to the level of expertise in climate science. Of scientists who were non-climatologists and didn't publish research, 77% answered yes. In contrast, 97.5% of climatologists who actively publish research on climate change responded yes. As the level of active research and specialization in climate science increases, so does agreement that humans are significantly changing global temperatures.
Figure 1. Response to the survey question "Do you think human activity is a significant contributing factor in changing mean global temperatures?" (0Doran 2009) General public data come from a 2008 Gallup poll.
More on the consensus surveys in a blog post by Dr. Jeff Masters.
Most striking is the divide between expert climate scientists (97.4%) and the general public (58%). The paper concludes:
"It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes. The challenge, rather, appears to be how to effectively communicate this fact to policy makers and to a public that continues to mistakenly perceive debate among scientists."
This overwhelming consensus among climate experts is confirmed by an independent study that surveys all climate scientists who have publicly signed declarations supporting or rejecting the consensus. They find between 97% to 98% of climate experts support the consensus (Anderegg 2010). Moreover, they examine the number of publications by each scientist as a measure of expertise in climate science. They find the average number of publications by unconvinced scientists (eg - skeptics) is around half the number by scientists convinced by the evidence. Not only is there a vast difference in the number of convinced versus unconvinced scientists, there is also a considerable gap in expertise between the two groups.
Figure 2. Distribution of the number of researchers convinced by the evidence of anthropogenic climate change and unconvinced by the evidence with a given number of total climate publications (Anderegg 2010).
Scientific organizations endorsing the consensus
The following scientific organizations endorse the consensus position that "most of the global warming in recent decades can be attributed to human activities":
- American Association for the Advancement of Science
- American Astronomical Society
- American Chemical Society
- American Geophysical Union
- American Institute of Physics
- American Meteorological Society
- American Physical Society
- Australian Meteorological and Oceanographic Society
- Australian Bureau of Meteorology and the CSIRO
- British Antarctic Survey
- Canadian Foundation for Climate and Atmospheric Sciences
- Canadian Meteorological and Oceanographic Society
- Environmental Protection Agency
- European Federation of Geologists
- European Geosciences Union
- European Physical Society
- Federation of American Scientists
- Federation of Australian Scientific and Technological Societies
- Geological Society of America
- Geological Society of Australia
- International Union for Quaternary Research (INQUA)
- International Union of Geodesy and Geophysics
- National Center for Atmospheric Research
- National Oceanic and Atmospheric Administration
- Royal Meteorological Society
- Royal Society of the UK
The Academies of Science from 19 different countries all endorse the consensus. 11 countries have signed a joint statement endorsing the consensus position:
- Academia Brasiliera de Ciencias (Brazil)
- Royal Society of Canada
- Chinese Academy of Sciences
- Academie des Sciences (France)
- Deutsche Akademie der Naturforscher Leopoldina (Germany)
- Indian National Science Academy
- Accademia dei Lincei (Italy)
- Science Council of Japan
- Russian Academy of Sciences
- Royal Society (United Kingdom)
- National Academy of Sciences (USA) (12 Mar 2009 news release)
"Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver. These conclusions are based on multiple independent lines of evidence, and contrary assertions are inconsistent with an objective assessment of the vast body of peer-reviewed science."
The consensus is also endorsed by a Joint statement by the Network of African Science Academies (NASAC), including the following bodies:
- African Academy of Sciences
- Cameroon Academy of Sciences
- Ghana Academy of Arts and Sciences
- Kenya National Academy of Sciences
- Madagascar's National Academy of Arts, Letters and Sciences
- Nigerian Academy of Sciences
- l'Academie des Sciences et Techniques du Senegal
- Uganda National Academy of Sciences
- Academy of Science of South Africa
- Tanzania Academy of Sciences
- Zimbabwe Academy of Sciences
- Zambia Academy of Sciences
- Sudan Academy of Sciences
Two other Academies of Sciences that endorse the consensus: