You’ve probably heard the statistic before. 97% percent of scientists agree that global warming is real.  People throw this number around, but where did it come from, and what exactly does it mean? Here at UseYourBrainForScience.com, we’re all about facts (though apparently not about brevity in our blog name), so here’s the skinny on this often misquoted number.

First, the statement above  is wrong.

97% of scientists don’t agree that global warming is real.  This statement is over-simplified, and very much misquoted.  The actual statement, which comes from two separate publications by Cook et al  (2013 and 2016) is “Among abstracts expressing a position on AGW [anthropogenic global warming], 97.1% endorsed the consensus position that humans are causing global warming”.  What Dr. Cook (A climate researcher from Australia) and his team did was review all the peer-reviewed work on the subject and determine what percent of this work in which a cause for global warming was discussed attributed the warming trend to human activity. Pretty straightforward, right?

So this is a little different than the statement I made in the first paragraph. This has several important implications.

1)  The 97% refers to the cause of global warming being humans, not belief in global warming itself. While there is no data on what percent of scientists actually agree that global warming is real, I would guess it is pretty much 100%. Why? Well, because of this..

 Source: http://ete.cet.edu/gcc

It’s tough to argue with that.  By definition, higher temperatures equals global warming, so if the average global temperature increases, then the globe is in fact warmer, which is… global warming.  You wouldn’t be much of a scientist if you reached any other conclusion from the data above.  This data, by the way, was generated by NASA. They are pretty good at science.

2) The 97% doesn’t refer to specifically to the percent of scientists who agree humans are causing global warming, but rather the percent of peer-reviewed reports that agree with this statement. Cook et al also did the calculation by percent of scientists.  That number is actually a little higher – 98.4% of the total authors of these papers believe that humans are causing global warming.

3) So that means that 3% of the peer-reviewed reports and 1.6% of total authors don’t think humans are causing global warming right?  Wrong.  Cook et al also took into account reports and authors that felt that cause was still uncertain.  1% and 0.4% (reports and authors, respectively) were uncertain, which leaves only 1.9% and 1.2% (of reports and authors) that disagreed with the consensus that humans are causing global warming.

4) Cook et al focused on peer-reviewed reports on global warming, which means that the authors in question are climate scientists, not scientists in general.  This is a good thing – they are the experts after all.

So there you have it. It’s probably safe to say that 100% of climate scientists believe  that global warming is real and that 98% of these scientists agree that humans are causing global warming. Feel free to use your detailed knowledge of this work at your next cocktail party. Nothing says “let’s party” like an in-depth discussion of climate science.  Right?

Primary Data from Cook et al (2013 & 2016)

http://iopscience.iop.org/article/10.1088/1748-9326/8/2/024024/meta

http://iopscience.iop.org/article/10.1088/1748-9326/11/4/048002/meta