The Cook et al paper ‘Quantifying the consensus on anthropogenic global warming in the scientific literature’ has been the top-ranking paper in terms of press citations, with Barack Obama using it to justify his efforts in Paris to lead the world in the war on CO2.
A typical press report on the study, reproduced in full below, advises in the first paragraph that ninety-seven percent of scientists say global warming is mainly man-made and the study found an overwhelming view among scientists that “human activity, led by the use of fossil fuels”, was the main cause of rising temperatures in recent decades. That looks like strong support for action on fossil fuels, but what does the paper itself tell us? Does it tell us anything more than that there is an overwhelming consensus on a human contribution to warming? Is that exciting news? Can you find anyone among the so-called deniers who denies that there has been warming since the industrial revolution? Do any of the “deniers” dispute a human contribution, if only in the heat-island effect of cities and towns?
What does the paper tell us about the agreement on amount of warming, the need to be alarmed about warming, the size of the human contribution and the role of CO2? As far as I can see, after reading the paper several times:
- The consensus in the paper does not refer to any particular amount of warming.
- There is nothing about a need to be alarmed.
- There is agreement that humans have contributed, but there is nothing about how much humans have contributed.
- There is no mention of the contribution of CO2.
I will not dwell on the way the Cook study was conducted, other than to note the method has been subjected to a great deal of criticism. Rather, my focus is on the published results and what they say, and do not say, about questions which matter if you have concerns about the trillions of dollars being sunk around the world in the suppression of CO2 emissions.
Turning to the paper, it is clear from the way the paper is organized that they wanted to say
- x% of scientists believe in warming
- y% think humans contribute and
- z% consider that human activity is the major driver.
They got what they wanted for x and y, namely 97+%, but z is missing. Of course the authors obtained a value because Table 1 shows how the data were classified to find it. However it is not in the paper. It is possible that the number is small to sustain the case for alarm about CO2. The research was clearly designed to provide a number for three levels of endorsement of the consensus.
- First “explicit endorsement (of humans as the primary cause of recent warming) with quantification”.
- Second “explicit endorsement without quantification”.
- Third “implicit endorsement”.
In the results (Table 2) the three categories are collapsed into one. Presumably if a significant number had turned up in the category which identified humans as the primary cause of warming it would have been reported because it is the figure that matters when you consider whether there is any need to address CO2 emissions. So the three levels of endorsement are collapsed into a figure of 97.1 for those who endorsed the “scientific consensus”.
It is clear from the way the authors talk that, for them, the consensus is not just warming but alarming warming with humans as the major cause. But that is not the consensus revealed in their own figures.
The results support (1) the proposition that there has been warming which is not in dispute and (2) the proposition that human activity makes a contribution, which by itself is hardly controversial. The paper makes no apparent contribution to the key issues, namely the amount of warming, whether we need to worry about it, how much humans contribute and, most important, the role of CO2.
Cook produced a press release to report the main findings, but he went far beyond the evidence in the paper. Bear in mind that there is a world of difference between a human contribution to warming, which could be small or negligible, and humans causing warming to a degree that matters.
This suggests that the consensus paper adds nothing to the scientific discussion of climate change. It has been misread and misreported probably more than any other paper and has demonstrated the limited capacity to read and understand scientific paper on the part of our journalists, science reporters and everyone from Barack Obama down who have used the figure of 97.1% to demand policies which increase power prices and undermine the reliability of supply.
Hi. I’m John Cook, lead author of ‘Quantifying the consensus on anthropogenic global warming in the scientific literature’. In our paper, we measured the level of agreement that humans are causing global warming in peer-reviewed climate papers published between 1991 and 2011. In recent years, two studies have measured the level of agreement of human-caused warming in the scientific community.
Both papers found that among climate scientists actively publishing climate research, 97% agreed that humans are causing global warming. But scientists have to back up their opinions with evidence that survives the scrutiny of experts in their field. In other words, peer-reviewed research.
The first analysis of this type was by Naomi Oreskes, who in 2004 analysed publications in the Web of Science between 1993 and 2003 matching the search term ‘global climate change’. She found that out of 928 papers, none rejected the consensus position that humans are causing global warming. Our paper builds upon this research.
We expanded the search to cover the 21 years from 1991 to 2011. In addition to ‘global climate change’ papers, we also included papers matching the term ‘global warming’. This expanded the number of papers to over 12,000. We also divided Oreskes’ six categories into two sets: the type of research and the level of endorsement of human-caused global warming. Each abstract was classified according to whether it explicitly or implicitly endorsed or rejected human-caused global warming, or whether it took no position on the cause of warming. Out of the 12,000 papers, we identified just over 4,000 stating a position on human-caused global warming.
Among these 4,000 papers, 97.1% endorsed the consensus position that humans are causing global warming. In the second phase of our study, we asked the scientists who authored the studies to rate their own papers. 1,200 scientists responded to our invitation, so that just over 2,000 papers in total received a self-rating. Among the papers that were self-rated as stating a position on human-caused warming, 97.2% endorsed the consensus. These results are strikingly consistent with previous surveys.
Between 1991 and 2011, the percentage of endorsements among papers expressing a position on human-caused global warming marginally increased over time. In the abstract ratings, the consensus grew at a rate of 0.1% per year. In the self-ratings, it grew by 0.35% per year, in both cases reaching about 98% consensus in 2011.
However, there is a significant gap between public perception and the actual 97% consensus. When a US representative sample was asked how many scientists agree that humans are causing global warming, the average answer was around 50%. This misperception has real-world consequences. When people correctly understand that the scientists agree on human-caused global warming, they’re more likely to support policy that mitigates climate change. This consensus gap is directly linked to a lack of public support for climate action. This underscores the importance of clearly communicating the consensus and closing the consensus gap.
Much of the press report is taken from Cook’s press release rather than the Cook et al paper itself.
The take-home message is in the first paragraph. Note the phrase “global warming is mainly man-made”. And in the following para “human activity, led by the use of fossil fuels, was the main cause of rising temperatures”.
The implication is that the results reported in the paper support those propositions. When you read the paper you find no sign of a consensus about warming being mainly man-made, or even an estimate of the human contribution. Similarly, the press report refers to the use of fossil fuels. But there is nothing in the paper itself about fossil fuels or CO2. The press report on the contents of the published paper is fake news, on the back of the author’s misleading press release. Actually, as the press release does not mention fossil fuels, the Reuters reporters simply added it in!
Ninety-seven percent of scientists say global warming is mainly man-made but a wide public belief that experts are divided is making it harder to gain support for policies to curb climate change, an international study showed on Thursday.
The report found an overwhelming view among scientists that human activity, led by the use of fossil fuels, was the main cause of rising temperatures in recent decades.
“There is a strong scientific agreement about the cause of climate change, despite public perceptions to the contrary,”
“There is a gaping chasm between the actual consensus and the public perception… When people understand that scientists agree on global warming, they’re more likely to support policies that take action on it.”
Global average surface temperatures have risen by 0.8 degree Celsius (1.4F) since the Industrial Revolution.
Experts in Australia, the United States, Britain and Canada studied 4,000 summaries of peer-reviewed papers in journals giving a view about climate change since the early 1990s and found that 97 percent said it was mainly caused by humans.
They also asked authors for their views and found a 97 percent conviction from replies covering 2,000 papers. The data will be released at (www.skepticalscience.com).
The report said it was the biggest review so far of scientific opinion on climate change.
“If people disagree with what we’ve found we want to know,” said Mark Richardson of the University of Reading in England, one of the authors of the study that looked at English-language studies by authors in more than 90 nations.
Another co-author, Dana Nuccitelli of Skeptical Science, said she was encouraging scientists to stress the consensus “at every opportunity, particularly in media interviews”.
Opinion polls in some countries show widespread belief that scientists disagree about whether climate change is caused by human activities or is part of natural swings such as in the sun’s output.
Rising concentrations of carbon dioxide, the main greenhouse gas, hit 400 parts per million in the atmosphere last week, the highest in perhaps 3 million years.
Governments have agreed to work out, by the end of 2015, a deal to slow climate change that a U.N. panel of experts says will cause more floods, droughts and rising sea levels.