“Citizen Science”: Scientific Consensus On Global Warming

I came across an interesting study about the consensus in the scientific community on anthropogenic global warming (AGW), i.e. the idea that human activity is very likely causing most of global warming. What makes this study so interesting is the fact that it involved a “citizen science” approach. Volunteers who contributed to the Skeptical Science website were asked to grade the abstracts of 11,944 scientific papers on global climate change that were published in the years 1991-2011.  These volunteers assessed whether the abstracts explicitly or implicitly endorsed AGW, were neutral on this question or whether they explicitly or implicitly rejected the idea that human activity is the main cause of global warming.

The study entitled “Quantifying the consensus on anthropogenic global warming in the scientific literature” was published by John Cook and colleagues as an open access paper in the journal Environmental Research Letters. The results are no surprise to anyone who has been following the scientific literature on AGW. Of the abstracts that expressed an opinion on AGW, 97.1% explicitly or implicitly stated that humans were the primary cause of global warming. This high level of consensus on the primary human role in causing global warming is very consistent with prior publications in the field. When Cook and colleagues contacted the authors of the papers to obtain their own opinion on the matter, they found that 98% of the authors who had a clear position on climate change agreed on human activity being the major cause of global warming.


Even though I think that the conclusions of the study are correct and that there is indeed a 97-98% consensus among scientists on AGW, I feel that the study highlights the potential for bias in “citizen science”.

The idea of using “citizens”, i.e. volunteers who are not necessarily trained as scientists to help obtain data is very intriguing. However, I do not believe that the authors of the study adequately addressed the issue of potential bias among these volunteers. The paper mentions that they contributed to the website Skeptical Science, which is managed by John Cook and attempts to convert climate change skeptics, i.e. people who deny the primary role of humans in global warming. I suspect that the volunteers who contribute to the website are probably all strongly convinced that AGW is very real. This could introduce a bias in the grading of the abstracts by these volunteers. I could not find any part of the paper, which discussed this potential bias and whether the authors also considered using “citizens” as abstract evaluators who did not believe in AGW or volunteers who felt neutral about AGW. Such “citizens” would have been good control groups to test whether a pre-existing opinion among volunteers can bias their interpretation of the scientific literature.

These concerns about potential “citizen science” bias should not only be addressed in the context of global warming research, but also in other areas of science that are associated with controversy and strongly held beliefs. A “citizen science” assessment of the risks and benefits of gene therapy or of embryonic stem cells in the scientific literature might also be influenced by their beliefs. As excited as many of us are about “citizen science”, it is necessary for us to consider potential biases that “citizens” can introduce, just like we also take into account the biases of professional scientists who conduct experiments when we evaluate a scientific paper.


Image credit: Annual average global warming by the year 2060 simulated and plotted via NASA)


3 thoughts on ““Citizen Science”: Scientific Consensus On Global Warming

  1. Khalil A. Cassimally

    97% of the abstracts point to clear manmade climate change. I’d think 1-2% of abstracts take a neutral standpoint. Be interesting to see who funds the studies in the remaining percentage points.


  2. Did you see Powell’s article about this?
    Only 24 of 13,950 articles, 0.17% or 1 in 581, clearly reject global warming or endorse a cause other than CO2 emissions for observed warming.
    These 13,950 articles have a total of 33,690 individual authors. The 24 rejecting papers have a total of 34 authors, about 1 in 1,000.

    I wrote a popular article about this, in Dutch though 🙂


  3. I came here via Prof Rehman’s article about the need for critical journalism. To that end, he and other readers here might be interested in the revelation that examination of Cook’s data has shown that more respondents completely rejected the idea of manmade climate change than felt that it was entirely due to man. The vast majority felt there was some manmade element, but only some.

    This makes the paper’s conclusions true, but only in a completely trivial way. Most prominent sceptics (myself included) would be happy to concur that CO2 affects the temperature. The real debate is over how much and over what timescales.


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