Getting Warmer

I think by now most people are familiar with the basic idea of global warming: the hypothesis that the Earth is getting warmer because human activities (notably the heavy use of fossil fuels) have increased the concentration of “greenhouse gases” (such as carbon dioxide, or methane) in the atmosphere, causing more heat to be retained and less to be radiated into space.   Although I think it is fair to say that the consensus among scientists is that something like global warming is going on, the idea has generated a lively argument, and a group of fairly vocal skeptics.  Some skeptics accept the evidence that the planet’s temperature is rising, but question whether this is attributable to human activities; others have expressed doubt that any change is really occurring at all.

The Associated Press, in an article carried at Yahoo!, reports on a newly-released study, carried out by a prominent scientist heretofore skeptical of the change, that will probably not be welcome news to that second group of skeptics.

A prominent physicist and skeptic of global warming spent two years trying to find out if mainstream climate scientists were wrong. In the end, he determined they were right: Temperatures really are rising rapidly.

The study, the Berkeley Earth project, was led  by Dr. Richard Muller, a physics professor at UC Berkeley, who also works at the Lawrence Berkeley National Laboratory.   Its independent analysis, based on temperature data since 1800 from 15 sources,  produced essentially the same results as earlier studies by NASA and the National Oceanographic and Atmospheric Administration [NOAA]: land temperatures  have risen by 1° C since the 1950s.

It is mildly amusing, in an ironic way, that a significant chunk of the funding for the study, according to the AP report,

… came from the Charles Koch Foundation, whose founder is a major funder of skeptic groups and the tea party. The Koch brothers, Charles and David, run a large privately held company involved in oil and other industries, producing sizable greenhouse gas emissions

Skeptics had previously argued that the reported increase might not be real, because of two potential problems with the data:

  • The weather stations from which the data were collected provide inaccurate and unreliable measurements
  • Cities tend to be warmer than rural areas (for example, because asphalt absorbs solar heat better than trees), and create “heat islands” that may skew the reported data.

Dr. Muller and his colleagues examined both of those possibilities carefully, and found that they did not have any significant effect on the results.

“Our biggest surprise was that the new results agreed so closely with the warming values published previously by other teams in the US and the UK,” said Richard Muller. “This confirms that these studies were done carefully and the potential biases identified by climate change skeptics did not seriously affect their conclusions.”

The four draft papers from the project, which are in the process of peer review, are available at the project site.   Dr. Muller also wrote an editorial at the Wall Street Journal site, in which he says that, although there may have been grounds for skepticism originally, the issues have now been explored and should be put behind us.

When we began our study, we felt that skeptics had raised legitimate issues, and we didn’t know what we’d find. Our 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.

The Berkeley study looked specifically at the question of urban “heat islands”, by looking at the results using only “very rural” locations.  They found no significant difference from the overall results.

The result showed a temperature increase similar to that found by other groups. Only 0.5% of the globe is urbanized, so it makes sense that even a 2ºC rise in urban regions would contribute negligibly to the global average.

Similarly, although it is true that the data quality from some weather stations leaves a good deal to be desired, there is no evidence that this affected the results.  The study looked separately at stations rated as having good accuracy, and those whose accuracy was rated as poor.  Once again, there was no significant difference in the results.

Remarkably, the poorly ranked stations showed no greater temperature increases than the better ones. The mostly likely explanation is that while low-quality stations may give incorrect absolute temperatures, they still accurately track temperature changes.

That last point is quite an important one.  What we are interested in is the change, if any, over the time period studied.  If poor quality stations  just provide data with a lot of random noise, that will tend to average out over a large sample; even if those stations provide biased data (for example, they always report the temperature 5° F too high), that will not affect the measured temperature difference.  Similarly, if we think about the potential “heat island” effect, if it were constant, it would not affect measurements of temperature change.  A misleading result might be obtained if a significant proportion of the area surveyed changed from being rural to urban over the survey period, but I rather doubt any such change has happened since the 1950s.  (If we were looking at data since, say, 1500, this might be a noticeable effect.)

In the WSJ editorial, Dr. Muller expresses the hope that these results will allow everyone to accept that the world is getting warmer, and focus on the questions of why this is happening, and what to do about it.

Global warming is real. Perhaps our results will help cool this portion of the climate debate. How much of the warming is due to humans and what will be the likely effects?

I’m afraid he is a bit more optimistic than I am about moving forward; as George Bernard Shaw put it:

Reformers have the idea that change can be achieved by brute sanity.

Nonetheless, having additional carefully collected evidence is a good thing.

There are additional reports on this research at Ars Technica and the New Scientist.

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