Yet Another Study Debunks “warming pause” Myth

Even as he continues to double down, Rep. Lamar Smith’s holy war against science is on shakier ground than ever. #lamarlysenko.

Chris Mooney in the Washington Post:

Even as Lamar Smith, chairman of the House Committee on Science, Space, and Technology, continues to investigate a high profile study from federal scientists debunking the idea of a global warming slowdown or “pause,” a new study reaches the same conclusion — in a different yet complementary way.

“There is no substantive evidence for a ‘pause’ or ‘hiatus’ in warming,” write Stephan Lewandowsky, a professor at the University of Bristol in the UK, and two colleagues in Tuesday’s Nature Scientific Reports. “We suggest that the use of those terms is therefore inaccurate.”
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Perhaps most notably, the new study uses a different temperature dataset kept by NASA, not NOAA, in its analysis. “You can definitely 100 percent say that our conclusion does not depend on the NOAA update,” says Lewandowsky. “We did not use the NOAA data.” The implication is that independent of Smith’s inquiry, the “pause” argument could still be invalid.

The new paper begins with a simple scientific literature review, finding that while there are many scientific publications citing the “pause” and trying to explain it, they aren’t very clear on its start date. Rather, start dates range from 1993 to 2003, although many start with 1998, a very hot El Nino year and at the time the hottest year on record (which serves to dampen the assessment of the rising temperature trend if this start date is chosen).

That in itself is odd, the paper contends, in that there never seems to have been a clearly accepted definition of the “pause” or “hiatus.”

The study also undertakes a statistical analysis of observed temperature trends, finding that if you select a short enough time period, it is quite easy to find a ‘pause’ in the rise of global temperatures — and if you select a long enough one, it goes away.

“At every year (vantage point) during the past 30 years, the immediately preceding warming trend was always significant when 17 years (or more) were included in the calculation,” the researchers find. However shorter periods often show a “pause,” they add.

“If you look at time periods of the same duration as the pause in the literature, then you find that the climate has ‘paused’ between 30 and 40 percent of the time, during which temperatures went up more than 1 degree Fahrenheit,” says Lewandowsky.

Guardian:

While this sounds compelling so far, the authors went even further. They subjected the data to a blind expert test. They evaluated people’s forecasting judgement because it reveals human perception of a particular set of data. The authors asked a group of economists (each with a Masters or PhD degree in economics or an allied discipline) to evaluate the trend in global temperatures without awareness of the source of the data.

The experts were told that the data referred to agricultural output and were asked questions about whether the agricultural output had “stopped”. In fact, the authors took exact statements from a climate contrarian, except they replaced words associated with global warming with statements associated with agricultural productivity.

In this blind test, the experts strongly rejected the agricultural “pause” conclusion. In fact, they found mention of a pause “to be misleading and ill-informed”. The experts were divided about whether the “pause” statement was also fraudulent. What is particularly convincing is that a blind test like this, which removes the effects of personal biases or preconceived opinions, is the gold standard for many research areas.

The authors continue the paper by reciting how the “pause” gained such traction in the general public and such interest among scientists. They also found that the intense investigation on the “pause” has, as they put it,

ultimately reaffirmed the overall reliability of climate models for projecting temperature trends. However, by accepting the framing of a recent fluctuation as a ‘pause’ or ‘hiatus’, that research has, ironically and unwittingly, entrenched the notion of a ‘pause’ in the literature as well as in the public’s mind.

I asked the lead author, Dr. Stephan Lewandowsky for a summary and he told me,

We put the idea of a ‘pause’ in global warming to a blind expert test. Basically, we presented the global temperature data for the last 100+ years to a group of economists, but identified the data as representing ‘world agricultural output’ so that political attitudes or preconceived notions would not play a role. The economists agree that talk of global warming having ‘stopped’ was misleading and not supported by the data. This is not surprising because if you do the statistical analyses you find that the most recent fluctuation in warming rate was no more extreme than previous accelerations. Global warming has not ‘paused’