Even as Lamar Smith, R-Texas, 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.”
The study at issue in Smith’s inquiry, published by scientists with the National Oceanic and Atmospheric Administration (NOAA) in the journal Science, updated an influential NOAA dataset to resolve discrepancies between certain types temperature measurements — and that’s when the “pause” disappeared. But the new study takes a different approach — it suggests that scientists have had curiously inconsistent definitions of the “pause,” and whenever you take a long enough period of climate history, there’s always an upward trend anyway.
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.”
“This apparent lack of clear and a priori criteria must be of concern in the statistical environment in which the ‘hiatus’ has unfolded, which is known to be sensitive to the particular choice of start and end points that define short-term trends and the comparison baseline,” the researchers write.
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.
The notion of a “pause” has long been a major argument for global warming doubters. But 2014 and 2015 appear poised to see back-to-back temperature records – even as more and more scientific criticism aimed at the “pause” idea has emerged.
Indeed, the new Lewandowsky paper, co-authored with climate researcher James Risbey of Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Harvard historian of science Naomi Oreskes, is part of a triumvirate of interdisciplinary studies by this team, debunking the “pause” using a variety of tools including social scientific techniques (Lewandowsky is a psychologist by training). The researchers have already found that in blind expert tests, 25 economists examining various temperature trends did not observe a “pause” – and have also suggested, with a larger group of collaborators, that scientists have fallen prey to the “pause” narrative because of a “seepage” of arguments by climate change doubters into the scientific literature.
“Basically our argument is that there is no such thing as a pause in global warming, and in fact, arguably there never has been,” says Lewandowsky. “What there has been is a fluctuation in warming, and they always occur,” he adds.
Even if the authors are right, that does not mean that prior studies into the “pause” weren’t valuable. They tended to focus on natural fluctuations that impact the rate of global warming, such as the behavior of the vast Pacific ocean. This adds to our overall understanding of the complex climate system.
However, scientists have long said that while natural fluctuations mean that not every year will be hotter than the next, an overall warming trend due to global warming is clear.
Above all, the new wave of studies challenging the “pause” lend an exclamation point to that conclusion. As does 2015: It isn’t even over yet, but scientists are already proclaiming it will be the hottest year on record, and by a very significant margin.
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