The End of Climategate?

New data on global temperature trends sheds light on the 2009 climate change scandal.

Climategate erupted into public with the release in November 2009 of thousands of emails sent to and from researchers associated with the Climatic Research Unit (CRU) at the University of East Anglia. It became a scandal because some of the emails seemed to suggest that prominent climate researchers may have fiddled with historical climate data with the goal of making recent increases in global average temperature look worse than it is. Suspicion was cast on three sets of historical temperature data, Hadley Centre/CRU series, the NASA Goddard Institute for Space Studies (GISS) series, and a third one from National Oceanic and Atmospheric Administration (NOAA).

As a possible example of scientifically illegitimate manipulation, skeptics pointed to an email from National Center for Atmospheric Research climate scientist Tom Wigley where he mentioned lowering mid-20th century temperatures by 0.15°C. This would have the effect of making the later increase of global temperatures look steeper.

In another email from CRU head Phil Jones reported, "I've just completed Mike's Nature trick of adding in the real temps ?to each series for the last 20 years (ie from 1981 onwards) amd from ?1961 for Keith's to hide the decline." Skeptics decried this "trick" because it tacked (largely without acknowledging it) thermometer data onto the end of a tree ring data series where the complete set of tree ring data suggested that temperatures had actually declined rather than increased. A graphic using the adjusted data showing a recent sharp increase in northern hemisphere temperatures was published as the cover of the World Meteorological Association's statement [PDF] on the status of the climate in 1999.

Were global warming proponents cherry-picking temperature data to bolster their claims that the world was becoming substantially warmer because of the emissions of greenhouse gases from burning fossil fuels? As University of Colorado environmental studies professor Roger Pielke Jr. told me back in 2009, "If it turns out that the choices made by CRU, GISS, NOAA fall on the 'maximize historical trends' end of the scale that will not help their perceived credibility for obvious reasons." On the other hand, Pielke added that Climategate could dissipate if probing by outside researchers finds that CRU, GISS, and NOAA researchers made temperature data adjustments "in the middle of the range or even low end, then this will enhance their credibility."

In 2010, University of California physicist Richard Muller decided to become just such an outside researcher. Why? In a lecture back in October 1, 2010, Muller made it clear that he was extremely provoked  by the implications of the "hide the decline" adjustments made to the tree ring data. Consequently, Muller established that Berkeley Earth Surface Temperature (BEST) group* with the goal of checking the accuracy of the temperature datasets assembled by the climatologists involved in Climategate.

Putting aside the possibility of unwitting or witting data manipulation, global warming skeptics were also concerned about the quality of the data used to determine temperature trends. They pointed out that many weather stations were subject to the urban heat island effect as cities grew around them and that numerous changes in equipment and location could spuriously suggest rising temperatures. The BEST team created a vast new set of 1.6 billion temperature reports using raw temperature data from more than 39,000 unique measuring sites. The data come from five times more stations than are used to assemble the earlier datasets.

So what did the BEST team find? On October 20, BEST issued a press release that declared [PDF], "Despite issues raised by climate change skeptics, the Berkeley Earth Surface Temperature study finds reliable evidence of a rise in the average world land temperature of approximately 1°C since the 1950s." Muller added, "Our biggest surprise was that the new results agreed so closely with the warming values published previously by other teams in the U.S. and the U.K. This confirms that these studies were done carefully and that potential biases identified by climate skeptics did not seriously affect their conclusions." So much for that aspect of Climategate.

The BEST team focused on the land temperature data because those were considered to be the most likely ones to be biased. The team suggested that once ocean temperature data are included the increase since the 1950s in global average temperature would be reduced to about two-thirds of a degree centigrade. Muller stressed, "What Berkeley Earth has not done is make an independent assessment of how much of the observed warming is due to human actions." Nevertheless, one of the four studies issued by BEST looked at the influence of ocean currents on global temperature trends, specifically the effect of shifts in sea surface temperatures associated with the Atlantic Multidecadal Oscillation (AMO). The study acknowledged that either greenhouse gas increases or natural variation might be driving AMO temperature changes. If the latter, that would suggest "the human component of global warming may be somewhat overestimated."  

Naturally, proponents of anthropogenic global warming were pleased with the BEST results and skeptics disappointed. However, Muller told the BBC on October 29 that the BEST land data showed no indication  that man-made global warming has stopped or slowed down. He did also note that data combining land and ocean temperatures indicated that global temperature increases had slowed down in recent years. Interestingly, even some proponents of anthropogenic warming have accepted that "global surface temperatures did not rise between 1998 and 2008." They blame factors like natural variability and increased air pollution for the hiatus.

Muller's assertion about recent temperature trends incited skeptics and a member of Muller's BEST team, Georgia Tech climatologist Judith Curry. An article with the provocative headline, "Scientist who said climate change sceptics had been proved wrong accused of hiding truth by colleague," in the Sunday Daily Mail (U.K.) reported that Curry was accusing Muller of "trying to mislead the public by hiding the fact that BEST's research shows global warming has stopped." The article quotes Curry as asserting, "There is no scientific basis for saying that warming hasn't stopped. To say that there is detracts from the credibility of the data, which is very unfortunate."

It's surprising how quickly people jump to (apparently predetermined) conclusions when it comes to a slowly unfolding phenomenon like climate change. The Daily Mail article engendered a flood of headlines from warming skeptics including, "The Climate Scam Continues," and "Time for Another Climate Science Scandal."

However, it seems that Curry has learned a rueful lesson about answering leading questions from reporters. On her Climate Etc. blog she clearly states, "This is NOT a new scandal….There is NO comparison of this situation to Climategate." In fact, Curry and Muller talked together for 90 minutes earlier this week at the Third Santa Fe Conference on Global and Regional Climate Change. "I have to say that there isn't much that we disagree on," reports Curry. "So all in all, I am ok with what is going on in the BEST project." End of scandal.

Contacted via email, Curry tells me that she "does not regard their initial findings and analyses as the last word on any of this" but adds, "Their interpretation is not unreasonable." She pointed to the BEST FAQ on the issue which concludes that "the decadal fluctuations [in global temperatures] are too large to allow us to make decisive conclusions about long term trends based on close examination of periods as short as 13 to 15 years."

A new study [PDF] just now being published by a leading group of climate modelers argues that "temperature records of at least 17 years in length are required for identifying human effects on global-mean tropospheric temperature." Considering that the warming pause in some temperature records has already been going on for 13 to 15 years perhaps we will soon find out if the climate models are producing valid results or not and get a better idea of how much warming can be attributed to accumulating greenhouse gases. 

While statistical quibbling about its results will occur, the BEST project has set admirable standards of scientific transparency with regard to data and how it's treated. This will help repair a bit of the damage to the public's trust in climate science caused by the insular authoritarian-minded band of climate scientists involved in Climategate.

*Disclosure: BEST received some funding from the Charles G. Koch Foundation. His brother David is a trustee of Reason Foundation which publishes this website.

Ronald Bailey is Reason's science correspondent. His book Liberation Biology: The Scientific and Moral Case for the Biotech Revolution is available from Prometheus Books.