Sunday, October 07, 2012

No consensus on the "consensus": Michael Mann tries to turn 75 scientists into "perhaps 10K" scientists

Twitter / PapiTerra: @MichaelEMann Dr. Mann, would ...
@MichaelEMann Dr. Mann, would you have a ballpark number on how many scientists make up the 97% that agree on global warming?
Twitter / MichaelEMann: @PapiTerra would be in the ...
@PapiTerra would be in the thousands Steve, perhaps 10K or so, depending on how you define/count...
Flashback: Mutiny of the bounties - Watts Up With That?
What of the claim that “97% of climate scientists believe in AGW”? The origin of this spurious claim is a 2009 online survey of scientists by two University of Illinois professors who claimed to have found that 75 out of 77 climate scientists (yes, only 77 climate scientists!) answered yes to this question: “Do you think human activity is a significant contributing factor in changing mean global temperatures?” The sample size is bizarrely small – more about that in a moment — and the question itself is meaningless. Most “skeptics” believe “human activity” – which includes everything from clearing forests to make way for crops to the urban heat islands created by cities – is having some impact on global temperatures. This survey tells us nothing about the real issue about which AGW advocates claim a consensus, that human emissions of greenhouse gases are causing catastrophic climate change.

Regarding the sample size … according to Lawrence Solomon, the two researchers who produced the survey deliberately left out solar scientists, space scientists, cosmologists, physicists, meteorologists, and astronomers … all scientists likely to be aware of natural causes of climate change. Only scientists employed by governments or universities were chosen to be surveyed, introducing another source of bias. Of the 10,000 or so scientists left, about 3,000 replied to the 2-minute online survey. No surprise, 82% of that unrepresentative sample answered yes to the ambiguous question. The authors then looked at a subset of just 77 scientists who participated in the survey and were successful in getting more than half their papers accepted by peer-reviewed climate science journals and found that 75 of those answered “yes.” 75/77 = 97%.

This may be how sausage is made, but it is not how accurate surveys are conducted. The “97% of climate scientists” claim is garbage. Anyone who cites it ought to be ashamed.


kenneth said...

So, you are saying that 82% out of 3,000 replied "yes" ?

Thats a bit different than 72 out of 75?

But the question was....questionable...

DennisA said...

Kenneth said...

"Thats a bit different than 72 out of 75?"

The phrase “97 percent of the world's climate scientists” is the phrase normally used but the truth is somewhat different. According to the figures presented in the paper, 90% of the scientists were from the US, including federal and state bodies, 6% from Canada and 4%from 21 countries around the world.

We are also told that only 5% of the original sample response were climate scientists, so if we pragmatically apply those proportions we end up with just 141from the US, 9 from Canada and just 6 from 21 countries around the world, hardly a global consensus.

“In our survey, the most specialized and knowledgeable respondents (with regard to climate change) are those who listed climate science as their area of expertise and who also have published more than 50% of their recent peer-reviewed papers on the subject of climate change (79 individuals in total). Of these specialists, 96.2% (76 of 79) answered “risen” to question 1 and 97.4% (75 of 77) answered yes to question 2.”

Q1.When compared with pre-1800s levels, do you think that mean global temperatures have generally risen, fallen, or remained relatively constant?

Q2.Do you think human activity is a significant contributing factor in changing mean global temperatures?

The original number contacted was 10,157 and of those, 69% decided they didn’t want any part of it, but they were the original target population. When the figure of 75 believers is set against that number, we get a mere 0.73% of the scientists they contacted, who agreed with their loaded questions.

A headline of 0.73% doesn't quite have the same ring as 97% does it?

This CNN posting was typical of the Press coverage at the time:

"Surveyed scientists agree global warming is real January 19, 2009

A survey of more than 3,000 scientists found that the vast majority believe humans cause global warming.

Human-induced global warming is real, according to a recent U.S. survey based on the opinions of 3,146 scientists."

Not quite the full picture.....