A few responses on that Berkeley climate study

at 05:14 PM ET, 11/01/2011

From a purely scientific standpoint, it wasn’t terribly exciting to hear that a team of researchers based in UC Berkeley had taken a poke at the global temperature record and found that the Earth has indeed been heating up over the past century, just like NASA and other agencies have been saying all along.

Richard Muller displaying some results from the BEST study. (Paul Sakuma/AP)
Still, the leader of the Berkeley Earth Surface Temperature (BEST) team, Richard Muller, had been critical of climate scientists in the past, and his team had been partly funded by the Koch Foundation, so there was a man-bites-dog quality to the whole affair. “Even the doubters were getting on board,” etc. Not surprisingly, then, there’s been a lot of pushback from other climate skeptics who aren’t thrilled with the glowing coverage that Muller’s group is getting. Let’s go through a few of the responses so far:

1) “Muller’s not really a skeptic.” A bunch of conservative bloggers have criticized me for calling Muller a climate skeptic. They note that Muller has said before that he believes carbon dioxide is warming the planet. So let’s define terms. The phrase “climate skeptic” has frequently been used to characterize people who disagree with the mainstream scientific consensus on climate change. That’s broad enough to include a lot of different views. Some scientists who are widely considered skeptics, like MIT’s Richard Lindzen, also agree that CO2 can warm the Earth but sharply disagree with the vast majority of climatologists on how big the effect is. That’s what makes Lindzen a skeptic.

The fact that Muller agrees that CO2 can warm the planet doesn’t mean he’s in line with the mainstream consensus — it just means that he agrees with elementary facts about the greenhouse effect. Indeed, it’d be odd if he didn’t. Muller has, however, expressed a lot of doubts that the temperature record was reliable, especially after the Climategate affair broke. He told Science magazine that he considers noted skeptics like Anthony Watts and Steve McIntyre “heroes.” He’s savaged climate scientists like Michael Mann over the reliability of well-established paleoclimate records — earning him accolades from places like the Heritage Foundation. Muller may not be an outright denier like, oh, Rick Perry, but his past statements put him in the skeptic camp.

2) “The BEST studies don’t prove humans are warming the planet.” This much is true. Just because the Earth has been warming in the 20th century doesn’t, in itself, prove that humans are to blame. Though as I detailed in this post (or, better yet, check out the IPCC’s 2007 report), there’s ample evidence that increased atmospheric concentrations of greenhouse gases are the main driver of the 20th-century temperature rise — indeed, there isn’t any other theory that can explain why the Earth has heated up to the extent that it has. But, agreed, Muller’s team doesn’t provide evidence either way here.

3) “The BEST studies show that global warming has stopped.” One of the BEST researchers, climatologist Judith Curry, has been criticizing Muller for telling reporters that “We see no evidence of [global warming] having slowed down.” And the Daily Mail drew up a much-cited graph showing that, according to the BEST data, global warming appears to have stalled between 2001 and 2010.

There are a couple of problems with this line of argument. For one, as the BEST team noted in its FAQ, it’s just too hard to draw conclusions about long-term trends by looking at periods of less than 15 years. In the very short term, temperatures can fluctuate a fair bit due to natural variability, as, say, heat gets temporarily transferred to deeper ocean layers. (See the diagram on the right via Skeptical Science, which is purely for illustrative purposes, for an example of how very short-term trends can be misleading).

But perhaps more to the point, the “flat trendline” in the BEST data seems to be a statistical artifact due to two faulty data points in April and May of 2010 that were highly uncertain and based on readings from just 47 temperature stations (by contrast, the March 2010 temperature was based on 14,488 stations). When you remove these two highly suspect outliers, the BEST record shows a 0.14°C warming trend since 2001. And when you look at longer time periods, the upward trend is even more pronounced. There’s little here to suggest that global warming has somehow stopped.

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