In the rainy Brisbane summer of 2011, James Powell, a geochemist and National Science Board member, and John Cook, physicist and Climate Communication Fellow at the University of Queensland, began discussing an idea. Cook had been running the website Skeptical Science since 2007 explaining what peer-reviewed science had to say about global warming and, in this way, combatting global warming denial with reason and facts. He had written numerous papers, coauthored books, and won the Eureka Prize in 2011 for the advancement of climate change knowledge. All of this, on a shoestring budget helped by donations through the site.

Yet the public perception of climate change science and scientists worldwide remained muddied.

During his research on the psychology behind climate change denial, Cook kept circling back to the fact that the public were less likely to support policy action on an issue if they thought scientists were still debating that issue —a fact well known not only by social scientists, but companies and political strategists. In 2000, political consultant Frank Luntz advised the Republicans in the presidential election to adopt this strategy by making lack of scientific certainty a primary issue in the debate. His reasoning was that “should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly.” Funding for this strategy has been significant. An investigation by The Guardian this year found that from 2002 to 2010, conservative billionaires had contributed nearly $120 million to around 100 groups who were casting doubt on the science behind climate change.

This is called manufacturing doubt on the consensus, and it’s been a very effective strategy. A significant gap, known as the consensus gap, exists between public perception and scientific consensus. In the United States, on the facts of climate change, 43 percent of the population believe that climate scientists are still in disagreement about whether the Earth is getting warmer because of human activity. This is where Powell and Cook’s idea came about: review as many climate science papers as possible, analyze the data, find out the true state of the consensus, then publish the results. And so the Consensus Project was born.

The Work Begins

Over the next 12 months, volunteers on the Skeptical Science team, from countries including Australia, the United States, Canada, the United Kingdom, New Zealand, Germany, Finland, and Italy, pitched in to investigate the scientific consensus on climate change in the published literature.

Naomi Oreskes, co-author of the book Merchants of Doubt, had conducted similar research in 2004. Powell had a plan to replicate this study over the period from 1991 to 2011, tally the number of papers rejecting climate change, and promote the results through an organized social media campaign. Powell published his results on the website DeSmogBlog, and his infographic communicating the overwhelming consensus has been one of the most popular features on the website. Cook, working in parallel, took a more thorough approach: as well as identifying papers that rejected human-caused climate change, his analysis would rate how strongly papers either endorsed or rejected the consensus on climate change. The analysis would also survey the authors of the papers themselves and use peer review and social media for more impact.

The team ran keyword searches, collected papers, and then, using a custom web tool, analyzed each paper’s abstract. The abstracts were placed in one of seven possible categories including explicit or implicit endorsement of human-caused global warming, no position, and implicit or explicit rejection.

The second stage was to then ask the authors of each paper to rate their own papers on whether it expressed a position on human-caused global warming.

The stats are impressive. Overall, the team analyzed 12,464 climate papers from 1991 to 2011 across a wide range of fields and subjects. Of the 29,286 scientific authors who were identified from at least 84 countries, 1,200 weighed in on their work, with over 2,000 papers receiving a rating from the paper’s author.

And the Results Are In

The result of 12 months of research was a 97.2 percent consensus by the papers’ authors and a 97.1 percent consensus by the Skeptical Science team on human-caused global warming.

This was taken from 4,000 papers that expressed a position on climate change in their abstracts. It’s important to note that two thirds of the total 12,464 papers analyzed didn’t express a position in their abstracts. However, when these “no-position” papers’ authors were asked to rate their full papers, more than half indicated their full paper endorsed human-caused global warming.

This is not so surprising considering the word limits on abstracts, and the fact that scientists will “…generally focus their discussions on questions that are still disputed or unanswered rather than on matters about which everyone agrees.”

Importantly, the results also found that the consensus has grown over time – to 98 percent in 2011.

This is in line with the Intergovernmental Panel on Climate Change (IPCC), the leading expert body on climate change “regarded as the single most authoritative source of information on climate change and its potential impacts on environment and society” . The IPCC has issued a series of increasingly definitive statements on the attribution of recent global warming that represent the evolving consensus position. The IPCC Second Assessment Report stated, “The balance of evidence suggests that there is a discernible human influence on the global climate.” This position was strengthened in the Third Assessment Report in 2001, concluding that “most of the warming observed over the last 50 years is attributable to human activities.”

The strongest IPCC statement on attribution comes in the most recent Fifth Assessment Report. “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia,” concludes the report. “Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. This evidence for human

influence has grown since [the last assessment]. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”

Berkley Lab / Flickr

Open Access and Money

Two emerging trends helped Cook get the word out on the climate change consensus project.

One trend is open access publishing. From the Public Library of Science to outspoken advocates such as Aaron Schwartz and Michael Eisen, there have been increased calls for academic research to be made available not just to those within academia or those who can afford the high journal subscription fees, but to anyone around the world.

One issue is that most open access journals charge authors to publish an article.

Alongside open access, crowdsourced funding—asking people to donate money for an idea or project in return for being a part of the project or receiving rewards—is also gaining popularity. Kickstarter is one example of many.

The Skeptical Science team wanted to publish the paper via open access and make it available to as many people as possible. Using the idea of crowdsourced funding, they put a shout-out on their website on the 25th of April 2013 to help fund the publishing of this paper and only 9 hours later the team had raised $1,600.

So on May 16th, 2013, the paper “Quantifying the Consensus on Anthropogenic Global Warming in the Scientific Literature” was published in the peer-reviewed journal Environmental Research Letters.

Global Reaction to The Consensus Project

The best possible exposure for this research came through Barack Obama’s Twitter account. The day after publication, a tweet was made to his 31.5 million followers at the time: “Ninety-seven percent of scientists agree: #climate change is real, man-made and dangerous.”

And on Tuesday the 25th of June, 2013, Obama gave a signature speech on climate change at Georgetown University. There, he said “so the question is not whether we need to act. The overwhelming judgment of science—of chemistry and physics and millions of measurements—has put all that to rest. Ninety-seven percent of scientists, including, by the way, some who originally disputed the data, have now put that to rest.”

In the UK, the Minister for Energy & Climate Change, Gregory Barker also cited the article in a speech. Interviews and articles appeared in the media worldwide.

In terms of online impact, according to Altmetric, which measures the online buzz around academic articles, this paper is in the top 5% of all academic papers and the top 1 percent of all papers published at a similar time.

Within a few weeks, the paper had reached 50,000 downloads, making it the most downloaded paper at Environmental Research Letters.

Why is this work important?

People who understand and perceive the actual scientific consensus on human-caused global warming are more likely to support government action to deal with the issue. This has been shown in several studies , and people will defer to the judgment of experts as they trust climate scientists on the subject of global warming. The issue is therefore communicating this agreement to the public.

This research is extremely important in bringing to light the real facts about manmade climate change and communicating this to the world.

“Consensus doesn’t prove human-caused global warming. Instead, the body of evidence supporting human-caused global warming has led to a scientific consensus.” The Consensus Project shows what can be achieved when you combine the ingredients of limited cash resources, motivated social scientists, volunteers, technology, crowdsourced funding, and open access publishing.