The consensus of the 2.45%

The previous post was about the consensus according to Naomi Oreskes. It was clear that the consensus statement was surprisingly uncontroversial, a statement even skeptics would certainly agree with. Another survey that is mentioned often is Examining the Scientific Consensus on Climate Change from Peter Doran and Maggie Kendall Zimmerman in 2009.

Basically, an invitation to participate in a survey consisting of two questions on global temperatures and some questions about their field of expertise. The invitation was sent to 10,257 Earth scientists and they received 3,146 completed surveys. From these completed surveys Doran and Zimmerman separated 79 scientists that listed climate science as their area of expertise and who also published more than 50% of their peer reviewed papers on the subject of climate change. The answers of those 79 scientists on the two questions influenced the result: ≈97% agreed with those statements and therefor were part of the consensus.

Okaaaay, the result is based only on a sample of 79 scientists out of already a sample of 3,146?

Let’s first start with the questions:

1. When compared with pre-1800s levels, do you think that mean global temperatures have generally risen, fallen or remained relatively constant?
   76 out of 79 scientists answered “Risen” on this question, meaning 96.2%, which seems little to me.
2. Do you think human activity is a significant contributing factor in changing mean global temperatures?
   75 out of 77 scientists answered “Yes” to this question, meaning 97.4%. Which is also surprisingly little considering the broad and vague terms it was stated in.
   Only 77 of the sample of 79 because the second question was not asked to some surveyed. If they answered “remained” relatively constant” they didn’t get the second question. Which means two scientists selected that option in the first question and were not counted in the second, lifting the result by a couple percent in the process… This is the source of the 97%.

If I would have taken the survey I would have answered definitely “Risen” on the first question and a cautious “Yes” on the second one. Cautious because I believe human influence is only one of the many influences and a yes is closer than a no. It all depend on what one means with “significant”. It is a downright miracle that only 97% gave these answers on both questions! My take is that some (skeptic) scientists suspected a biased survey and answered differently on those questions.

Question 1. It depends on what one means with “pre-1800s” (just before 1800, middle of Little Ice Age, Medieval Warm Period,…). My take would be just before 1800. Since then temperatures went up. But even this doesn’t mean that much. Yes, temperatures starting to rise in the 1850s, no doubt about that, but this has probably more to do with the coming out the a cold period (called “The Little Ice Age” for a reason). The answers on this first question doesn’t say anything about the supposed (human) cause of the warming.

Question 2. That’s really vague. First it states “human activity” and not “anthropogenic CO₂ emissions”. Maybe there are other influences that Doran & Zimmerman mean? Like urbanization, agriculture, deforestation,… So even if some scientist doesn’t believe in the magical powers of CO₂ he/she could have answered “Yes” on that second question. Second, what is the meaning of “significant contributing factor”. That is highly subjective and the answer on this question will always be an opinion, not a fact. It is not possible to give a nice yes/no answer in a field that has no black/white answers.

Now why the narrow selecting of 77 and 79 scientists out of the 3.146 Earth scientists? Doran & Zimmerman explained it like this:

It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes

Okay, I can agree that the scientists who actively publish on climate science would know more than a thing or two about climate science. But that is not necessarily impressive in a chaotic system from which we don’t have much data yet. What about the other 97.5% that were tossed out? The results were lower in that group. With a very low score of the economic geologists (only 47% said “Yes” to the second question) and the meteorologists (only 64% said “Yes” to the second question).

Concluding: what exactly is that consensus in this publication about? The existence of an increase in global temperatures (which is rather uncontroversial) and a very vague “human activity” as a “significant contributing part” in global mean temperatures.

It seems to me this kind of consensus is basically meaningless.

But look closer to what wasn’t said: that this temperature increase is dangerous (therefor needing immediate action) or CO₂ did it (so we must take steps to curb it). But that is what we are being suggested that it means.