In 2004, Naomi Oreskes published the first analysis examining the scientific consensus on climate change in published peer-reviewed research. She scanned over 900 climate papers from 1993 to 2003 to determine how many papers rejected the proposition that humans caused global warming. Remarkably, she found zero rejection papers. Oreskes’ results were cited in An Inconvenient Truth to demonstrate the overwhelming scientific consensus on climate change
Since that time, several studies have further sought to measure the level of agreement among climate scientists. In 2009, Peter Doran and Maggie Zimmerman found that 97 percent of actively publishing climate scientists agreed that humans were significantly changing global temperatures. In 2010, William Anderegg led a study that similarly found 97 percent of scientists who published climate papers agreed with the consensus. Over time, the picture was becoming clearer—there was overwhelming agreement in the climate science community on the issue of human-caused global warming.
Earlier this month, I published a peer-reviewed paper that continued and extended the work of Naomi Oreskes. The study was a collaboration of a team of research volunteers from the website Skeptical Science, working together for over a year to produce the most comprehensive analysis of climate research to date. We added another decade’s worth of climate research, examining 21 years and over 12,000 climate papers from peer-reviewed scientific journals. Our goal was to quantify the level of consensus in climate research from 1991 to 2011. We also hoped to determine how the consensus changed over the last two decades.
What we found was strikingly consistent with earlier research. Out of all the climate papers that stated a position on human-caused global warming, 97 percent endorsed the consensus. Overwhelming agreement had already formed by the early 1990s.
Over the 21 year period, the consensus strengthened. The number of papers endorsing the consensus was increasing at an accelerating rate. Correspondingly, more and more scientists from all over the world were adding their names to the ranks of scientists endorsing human-caused global warming. By 2011, the end of the period we examined, the level of consensus was around 98 percent.
We also employed a novel technique to independently measure the consensus. We invited the scientists who authored the climate papers to rate the level of endorsement in their own published research. After all, who is a better expert on what a paper is saying than the very authors of the paper?
The result was eerily familiar. Out of all papers that scientists rated as expressing a position on human-caused global warming, 97 percent endorsed the consensus. The 97 percent figure, seen in several studies over the last few years and through two different measures in our own study, continued to assert itself.
Nevertheless, there is a gaping chasm between the actual consensus and public perception of the consensus. When asked how many climate scientists agree on human-caused global warming, the average answer from the general public is around 50 percent.
This misperception has persisted for several decades and hasn’t happened by accident. There has been a deliberate, focused attempt to confuse the public about the level of agreement between scientists for over 20 years. In 1991, Western Fuels Association spent half a million dollars on a campaign attacking the scientific consensus. Political pollster Frank Luntz advised Republicans to focus on casting doubt on consensus in a memo leaked in 2002. A 2012 analysis of conservative syndicated columns found that the number one climate myth promoted by conservative columnists was “there is no scientific consensus.”
Why such a focus on attacking the consensus? Studies in 2011 and 2013 found that when the public correctly understands that scientists agree on climate change, it is more likely to support policy to do something about it. Social scientists are coming to realize what opponents of climate action have known for decades. If you confuse the public about scientific consensus, you can delay meaningful climate action.
This is why Naomi Oreskes’ 2004 work on consensus was so important. It’s why our study finding a strengthening consensus is important. The significance of this message is demonstrated by the fact that our paper was recently tweeted by President Obama and, fittingly, Al Gore. We need to clearly and persistently communicate the fact that the scientific community agrees on climate change. Closing the consensus gap is an essential and important step towards meaningful climate action.
Editor's Note: You can find the results of their paper summarized at: theconsensusproject.com.