31 October 2011

A ‘Now What?’ Moment for Climate Change Skeptics

Skeptics and denialists of climate change lost a powerful voice recently. What’s more? It was one of their very few scientific voices.

Richard Muller, a physicist at the Universityof California at Berkeley, has long raised questions about the data used by climate researchers and the Intergovernmental Panel on Climate Change (IPCC) to chart the planet’s temperature record over the last 200 years or so: the chief evidence of recent and rapid warming. Among the questions were whether the data and the stations that collected it were of sufficient quality to allow for a valid estimate of warming; whether the data had been selectively chosen, or cherry-picked, to show a warming trend that would otherwise not be reflected; and whether urban heat-islands were skewing global average temperatures.

In an October 21 op-ed in the Wall Street Journal, Muller laid out a case for climate skepticism based on these questions. “Without good answers to all these complaints,” he wrote, “global-warming skepticism seems sensible.”

Feeling that earlier explanations from scientists fell short of adequately addressing these points, Muller and a team of physicists, statisticians and climatologists dubbed the Berkeley Earth Surface Temperature (BEST) project, went in search of the answers themselves. They assembled a dataset of 1.6 billion surface temperature records from 39,390 land-based stations (air temperatures over the ocean surface were not considered in the study), including the subset of records used by the IPCC. The IPCC and other groups such as NASA and the National Oceanic and Atmospheric Administration had limited the records used in their assessments to these stations because of concerns about data completeness and reliability from the other stations. As Muller pointed out in his Wall Street Journal piece, “There’s logic to that practice, but it could lead to selection bias.”

So what were the results of the BEST team’s two-year analysis? Contrary to the expectations of the skeptical crowd, and perhaps to Muller himself, the “results turned out to be close to those published by prior groups. We think that means that those groups had truly been very careful in their work, despite their inability to convince some skeptics of that. They managed to avoid bias in their data selection, homogenization and other corrections.”

And in conclusion, Muller wrote, “Global warming is real.”

The team’s analysis indicated a roughly 1 degree Celsius increase in the average global land surface temperature since the mid-1950s, in agreement with, if not even greater than, the IPCC’s estimate. The results suggested that while heat-island warming is large on local scales, it does not significantly affect the global average because of the relatively small portion of the planet — less than 1 percent — that is urbanized. Additionally, low-quality temperature stations — deemed so because they were poorly located, had been moved over time, or only gave short-term, incomplete or highly variable records — actually showed a similar warming trend to the high-quality trends. Thus, the outcome was essentially the same regardless of whether all of the temperature records were included or whether, as in the case of IPCC and other assessments, some data were excluded.

The team also found that about one-third of stations showed a cooling trend since the mid-20th century. But, the other two-thirds showed warming. As BEST lead scientist Robert Rohde noted in an October 20 pressrelease, “The large number of sites reporting cooling might help explain some of the skepticism of global warming.” The press release goes on to say that “the presence of sites reporting cooling is a symptom of the noise and local variations that can creep in.”

In closing his op-ed, Muller wrote that although no assessment of the role of humans was made in their study, “Perhaps our results will help cool this portion of the climate debate.”

If it could only be that easy. While those who have been celebrating the new findings can hope that at least some skeptics out there are as sensible as Muller and his team, many of the same people who held him up as a leader of opposition to climate alarmism are surely working out ways to disown and discredit him. (Perhaps they’ve already been hard at work considering Muller began tipping his hand about preliminary results earlier this year.) To do so, they will have to contend with not only the BEST team’s results, but the transparency with which it has conducted work can only help as well. In addition to pursuing traditional peer-reviewed critiques, BEST has opened up their data, methodologies, funding and drafts of the four scientific papers the team has prepared to public scrutiny.

Nonetheless, if critics can find legitimate inaccuracies in the analysis, or present valid, contradictory data of their own, then more power to them. Healthy skepticism in science is, after all, a good thing. It’s when that healthy skepticism becomes dogged and unwavering in the face of the preponderance of available evidence, however, that it becomes (at the very least) capricious and impractical.

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