"The seminal study in this area was done by Naomi Oreskes who surveyed 928 'global climate change' papers from 1993 to 2003," John Cook of the University of Queensland, Australia, told environmentalresearchweb. "She found zero papers rejecting the consensus that humans were causing global warming."

Cook and colleagues expanded Oreskes' search by adding another decade's worth of papers and including "global warming" papers, using volunteers to help rate the papers' position. "This swelled the number of papers to over 12,000," said Cook. "We confirmed Oreskes' result – among the papers matching her search parameters, zero rejected the consensus. We also did something not done before – inviting the scientists who authored the papers to independently rate their own research."

Again this resulted in a 97% consensus that man is causing climate change. In fact, this seems to be a commonly recurring figure – Cook says that two surveys of the climate-scientist community in recent years also found a 97% consensus.

"One study led by Peter Doran found that the greater the expertise in climate research, the higher the agreement that humans were causing global warming," he explained. "The other study, led by William Anderegg, surveyed public statements on climate change by 908 climate scientists."

According to Cook, the crowd-sourcing element of his team's project allowed analysis of samples an order of magnitude larger than in earlier studies. "Where Oreskes analysed 928 papers, our team analysed over 12,000 papers," he said. "Where Anderegg surveyed 908 climate scientists authoring public statements on human-caused global warming, we identified 10,356 scientists stating a position on human-caused global warming in peer-reviewed papers."

The consensus formed in the early 1990s and has strengthened since, the team discovered. "Our finding of near unanimous agreement among scientists is in stark contrast to public perception, with only half of the general public thinking scientists agree on global warming," said Cook. "The gap between public perception and the 97% reality has real-world consequences. People who correctly perceive the scientific consensus are more likely to support policies to mitigate climate change. This underscores the importance of 'closing the consensus gap'."

The team's goal was to complete the most comprehensive analysis of peer-reviewed climate papers to date, says Cook. The researchers covered papers published from 1991 through 2011, using crowd-sourcing to spread the load over a team of volunteers from the Skeptical Science website. "It was also important to us that the paper was freely available to the public, which is why we chose the high-impact journal Environmental Research Letters," he said. "There's a $1,600 fee to make the paper open access, which we raised through crowd-funding on Skeptical Science."

Next the researchers plan to analyse papers published further back in time, as well as adding future research. "Hopefully, this will shed more light on when exactly the consensus formed," said Cook. "A common comment received from scientists rating their own papers was [that] we didn't include all their relevant research. This was a consequence of the particular search terms we used. We will explore broadening the search and expanding our crowd-sourcing process to make a larger sample size less prohibitive."

The team would also like to "examine the level of consensus across different degrees of 'expertise' in climate science".

The team, from the University of Queensland, Australia, Skeptical Science, the University of Reading, UK, Tetra Tech, Michigan Technological University, George Mason University, all in the US, and the University of Ottowa, Canada, reported their work in Environmental Research Letters (ERL).

Related links

Related stories