Sunday, May 29, 2016

Spencer on Bray and von Storch

An acquaintance directed me to this (originally WSJ commentary) piece by Dr. Roy Spencer as refutation of my consistently held characterization of the scientific consensus on anthropogenic (human caused) climate change as "overwhelming." The Spencer piece has a lot of problems. For example, he tries to debunk the scientific consensus by highlighting scientific disagreement over things like computer models and cloud formation:
Rigorous international surveys conducted by German scientists Dennis Bray and Hans von Storch—most recently published in Environmental Science & Policy in 2010—have found that most climate scientists disagree with the consensus on key issues such as the reliability of climate data and computer models. They do not believe that climate processes such as cloud formation and precipitation are sufficiently understood to predict future climate change.
This is an odd argument. The "consensus" has nothing to do with the reliability of models. It is all about two questions: Is the earth warming? Is that warming mostly caused by humans? Scientists reach conclusions about those questions in a variety of ways.

Many climate scientists don't see much need for models. James Hansen says that understanding how the climate has operated in the past tells us what we can expect in the future. I'd guess most scientists would say that models, alleged warts and all, can be useful for specific purposes, but the case for climate change doesn't depend upon how "good" those models are judged to be.

The Bray and von Storch survey does ask the two questions, ignored by Spencer, against which consensus is gauged, and is briefly mentioned in a Wikipedia article entitled "Surveys of scientists on climate change." From the article:
In the section on climate change impacts, questions 20 and 21 were relevant to scientific opinion on climate change. Question 20, "How convinced are you that climate change, whether natural or anthropogenic, is occurring now?" Answers: 67.1% very much convinced (7), 26.7% to some large extent (5–6), 6.2% said to some small extent (2–4), none said not at all. Question 21, "How convinced are you that most of recent or near future climate change is, or will be, a result of anthropogenic causes?" Answers: 34.6% very much convinced (7), 48.9% being convinced to a large extent (5–6), 15.1% to a small extent (2–4), and 1.35% not convinced at all (1).
Let me rephrase that slightly. On the question of whether the earth is warming,  93.8% said they were convinced at least to "some large extent," 6.2% were convinced "to some small extent," and nobody said they were completely unconvinced.

On the question of whether the warming was caused by humans, 83.5% said the were convinced at least "to a large extent," 15.1% "to a small extent," and a mere 1.35% were not convinced at all.

A very strong result for consensus.

I personally think the Bray and von Storch survey has some problems, as do most efforts of its kind. It's darned hard to survey scientists about their beliefs. But Spencer cited it to make his case, although as we can see it surely works against him.

With respect to the various survey attempts, the Wikipedia article says "they have generally concluded that the majority of scientists accept that human activity is contributing to global warming."

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