The PJ Tatler

New Excitement in the Climate Change Controversy (Updated)

Yesterday, Richard Mueller of UC Berkeley and the Berkeley Earth Surface Temperature (BEST) project published an op-ed in the New York Times headlined “The Conversion of a Climate-Change Skeptic.”  In it, he says:

Last year, following an intensive research effort involving a dozen scientists, I concluded that global warming was real and that the prior estimates of the rate of warming were correct. I’m now going a step further: Humans are almost entirely the cause.

My total turnaround, in such a short time, is the result of careful and objective analysis by the Berkeley Earth Surface Temperature project, which I founded with my daughter Elizabeth. Our results show that the average temperature of the earth’s land has risen by two and a half degrees Fahrenheit over the past 250 years, including an increase of one and a half degrees over the most recent 50 years. Moreover, it appears likely that essentially all of this increase results from the human emission of greenhouse gases.

Today, Anthony Watts of the Watts Up With That website announced and provided a paper (figures and tables here) in pre-print titled “An area and distance weighted analysis of the impacts of station exposure on the U.S. Historical Climatology Network temperatures and temperature trends.”

Watts is listed as lead author, with co-authors Evan Jones of New York; Stephen McIntyre of Toronto, Canada; and Dr. John R. Christy from the Department of Atmospheric Science, University of Alabama, Huntsville. In it, they demonstrate a systematic bias of about 0.15 degrees Celsius per decade in the United States Historical Climatology Network (USHCN) temperature estimates.

That is, they show that according to their methods, which are drawn from new UN World Meteorological Organization guidelines, the total warming in USHCN data are overstated — in fact, nearly doubled.

(For our more excitable commenters: “systematic bias” aren’t the words of Watts et. al., and they don’t mean a purposeful bias. “Systematic bias” is a term in statistics for any procedure that leads to “systematic error,” a procedural error that moves an observed statistic consistently in one direction. Go read the Wikipedia article linked and restrain yourselves from conspiracy theories.)

Roger A Pielke, Sr., a respected climate scientist, comments on the Watts et. al. paper on his blog:

Anthony has led what is a critically important assessment of the issue of station quality. Indeed, this type of analysis should have been performed by Tom Karl and Tom Peterson at NCDC, Jim Hansen at GISS and Phil Jones at the University of East Anglia (and Richard Muller). However, they apparently liked their answers and did not want to test the robustness of their findings.

In direct contradiction to Richard Muller’s BEST study, the new Watts et al 2012 paper has very effectively shown that a substantive warm bias exists even in the mean temperature trends. This type of bias certainly exists throughout the Global Historical Climate Network, as well as what Anthony has documented for the US Historical Climate Reference Network.

Now, I’ve only just skimmed the Watts et. al. paper, but its conclusions are very interesting: if they hold true, it appears to me that the BEST paper, which draws its data from the USHCN, may be flawed.


I’ve reached Dr. Judith Curry of Georgia Tech, who was a co-author of the first four BEST papers but who declined to be listed as an author of this one.  She was in an airport, and has promised me more tomorrow, but in the meantime she referred me to the New York Times Dot Earth blog and her quote:

The BEST team has produced the best land surface temperature data set that we currently have. It is best in the sense of including the most data and extending further back in time. The data quality control and processing use objective, statistically robust techniques. That said, the scientific analyses that the BEST team has done with the new data set are controversial, including the impact of station quality on interpreting temperature trends and the urban heat island effect.

Their latest paper on the 250-year record concludes that the best explanation for the observed warming is greenhouse gas emissions. Their analysis is way oversimplistic and not at all convincing in my opinion.

There is broad agreement that greenhouse gas emissions have contributed to the warming in the latter half of the 20th century; the big question is how much of this warming can we attribute to greenhouse gas emissions. I don’t think this question can be answered by the simple curve fitting used in this paper, and I don’t see that their paper adds anything to our understanding of the causes of the recent warming. That said, I think there are two interesting results in this paper, regarding their analysis of 19th century volcanoes and the impact on climate, and also the changes to the diurnal temperature range.

As usual, you have to look carefully at this. Curry strongly disagreed with the conclusions of the paper, and needs to be taken seriously: she is, after all, a co-author of the previous studies. Her point is simply that:

(1) the paper does say there has been warming, but well, everyone knew that. The question is the magnitude of the warming, the part of that which is anthropogenic, i.e., human-caused, and then what part of that part is caused by CO2. They have done a lot to clean up the data set, but as Watts et. al. note, that dataset may be subject to a systematic error.

(2) the strength of the conclusion that essentially all of that is both anthropogenic and caused by CO2 is being overstated. (My own choice of words would be “wildly overstated.”)

A couple of other links:

  • At Science Blogs, William Connolley calls the BEST announcement “rubbish.”
  • Steve Mosher and Zeke Hausfather have a detailed technical critique at Climate Etc, Judith Curry’s blog.
  • Andy Revkin has a relatively even-handed piece in his Dot Earth blog. (Note that Connolley comments there that he wasn’t saying that the conclusions of the BEST study were rubbish, but that Mueller himself is rubbish.  I’ve got to admit the argument there sort of escapes me, but the amusement value is enormous.)