During the past several years, some skeptics of manmade global warming have focused their attention on the reliability of the modern surface temperature record, which according to numerous studies, shows a distinct warming trend starting in the middle of the 20th century, and continuing through the present day.

The surface temperature record isn’t reliable, the skeptics argue, because the data is biased by the urban heat island effect, which can raise temperatures in cities compared to rural locations. And even if it isn’t biased because of the heat island effect, the skeptics reason, the record can’t be trusted because of the statistical methods scientists have used to account for missing or intermittent temperature data over time, and sparse data coverage across certain areas, like the Arctic.

Another common skeptic argument has been that too few surface observation stations are used for global climate change studies, and many of these stations suffer from data quality issues.

Now a new series of studies has come along, produced by someone known for his skepticism of mainstream climate science, which conclude that these skeptic arguments are simply not tenable.

Of course, there were previous studies showing that some, if not all, of these concerns had little factual basis – particularly concerning the urban heat island issue. But the skeptics ignored those, and the questions persisted, and grew louder in the wake of the so-called “climategate” email scandal that raised doubts about the credibility of one of the main sources of surface temperature data, the Climatic Research Unit at the University of East Anglia, in Britain. Texas Governor Rick Perry, for example, still makes references to the “climategate” dustup (among other reasons) in justifying his skepticism of manmade climate change, and the state of Texas cited concerns about the reliability of the surface record in a petition for the U.S. EPA to reconsider its finding that carbon dioxide, a climate-warming greenhouse gas, endangers public health and welfare.

Twelve month moving average of surface temperature record over land. New Berkeley temperature record, which agrees with other temperature records, shown in black ( Berkeley Earth Surface Temperature project)

The new studies will make it much, much harder to credibly cast suspicion upon the surface temperature record.

Known as the “Berkeley Earth Study,” the interdisciplinary collaboration headed by Richard Muller, a noted physicist, sought to directly address the legitimate questions concerning the reliability of the surface temperature record. The Berkeley Earth analysis shows 0.911 degrees Celsius of land warming (+/- 0.042 C) since the 1950s, which translates to about 1.8 degrees Fahrenheit.

The Berkeley study analyzed data from more than 39,000 weather stations, more than five times the 7,280 stations found in the Global Historical Climatology Network Monthly data set (GHCN-M) that has served as the foundation of many other climate studies. The researchers employed new statistical methods that, the team says, more accurately take into account discontinuities in the data as well as data quality questions.

From the Berkeley Earth Surface Temperature project: “Berkeley Earth video representation of the land surface temperature anomaly, 1800 to the present. The map of the world shows the temperature anomaly by location over time. The chart at the bottom, shows the global land-surface temperature anomaly. The Berkeley Earth analysis shows 0.911 degrees Centigrade of land warming (+/- 0.042 C) since the 1950s.”

Muller has (or had) credibility in the skeptic community due to his criticisms of mainstream climate science findings. So while the conclusions reached by Muller’s group are not exactly surprising, the source of those conclusions is noteworthy. (For more background info on Muller, I suggest reading this profile in The Guardian newspaper.)

The Berkeley team’s analysis strongly refutes claims that the urban heat island effect causes a warm temperature bias in the surface data. The researchers also found that despite the skeptics’ assertions, readings from networks of temperature stations are not compromised by poor data quality from many of the individual stations.

The Berkeley Earth Study should put the criticisms of the surface record to rest. As Andy Revkin of the New York Times’ Dot Earth blog wrote, “Muller’s work... appears to completely undercut efforts to raise doubts about the extent of recent warming.”

And as Muller himself wrote in an op-ed in the Wall Street Journal, a paper whose editorial board routinely casts doubt on the existence of global warming, let alone manmade global warming:

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. They managed to avoid bias in their data selection, homogenization and other corrections.

Global warming is real. Perhaps our results will help cool this portion of the climate debate…

I doubt Muller’s work will end the debate regarding the surface data, though, judging from the reactions of some climate skeptics. Blogger Anthony Watts, for example, who had previously written that he was “prepared to accept whatever result they produce, even if it proves my premise wrong,” slammed the Berkeley group for releasing its results before the studies underwent peer review.

“I know that I’ll be criticized for my position on this, since I said back in March that I would accept their findings whatever they were, but that was when I expected them to do science per the scientific process,” Watts wrote.

The irony in this reaction is that Watts and his contributors have long criticized the same peer review process, and they frequently post non-peer reviewed analyses and papers online.

Of Watts’ work, the Berkeley team states in a press release:

Stations ranked as “poor” in a survey by Anthony Watts and his team of the most important temperature recording stations in the U.S., (known as the USHCN -- the US Historical Climatology Network), showed the same pattern of global warming as stations ranked “OK”. Absolute temperatures of poor stations may be higher and less accurate, but the overall global warming trend is the same, and the Berkeley Earth analysis concludes that there is not any undue bias from including poor stations in the survey.

The Berkeley team has put its data and methods online, allowing for anyone to verify its work. This is a good sign, since it demonstrates that scientists have learned from “Climategate” and other recent pseudo-scandals that being transparent is the best way to earn credibility, rather than simply appealing to authority. Hopefully the peer review process (in the broadest meaning of that term) will bolster the studies’ findings when all is said and done, and we can finally move on to the more legitimately pressing questions in climate science, such as how high sea levels will rise between now and the end of this century.