The Earth’s average land temperature has warmed by around 0.9 degrees Celsius, probably down to manmade greenhouse gas emissions, according to new research from the Berkeley Earth Surface Temperature (BEST) project. Given that much of the media interest focuses on Muller’s suggestion that he is a converted skeptic, the findings of the work have been somewhat obscured. Here’s our guide to the research behind Muller’s self-described conversion.
What is BEST?
The BEST project was launched and chaired by Professor Richard Muller, a physicist at the University of California at Berkeley. It aims to address criticisms raised by climate skeptics about how existing records of the Earth’s average surface temperature have been compiled. Team members include physicist Robert Rohde, climatologist Judith Curry, and other physicists and statisticians.
Previous research from the BEST group, released in October 2011, addressed concerns raised by skeptics about records of surface temperatures, including the urban heat island effect and poor weather station siting. These issues were not found to have a significant effect on the global land surface temperature record.
What does the latest BEST research show?
This latest research from the BEST team confirms that the Earth’s average land temperature has risen by roughly 0.9 degrees Celsius since the 1950s, and by 1.5 degrees Celsius over the last 250 years. This is in line with existing records, which put average global land temperature rise over the last 50 years at 0.81 – 0.93 degrees Celsius:
The study also uses a simple model to work out whether the change in global land temperature fits best with changes in atmospheric carbon dioxide levels, volcanic activity or solar activity – and find the best fit with a combination of change in atmospheric carbon dioxide and volcanic activity:
The contribution of solar activity, it concludes, must be negligible.
Muller notes this doesn’t prove that carbon dioxide is responsible for warming, but adds:
“To be considered seriously, any alternative explanation must match the data at least as well as does carbon dioxide.”
How do the latest BEST results differ from previous studies?
The BEST temperature reconstruction of global land temperature records differs from other records – produced by the NOAA National Climatic Data Center (NCDC), the NASA Goddard Institute for Space Studies (GISS), and a collaboration between the UK Met Office Hadley Centre and the Climatic Research Unit at the University of East Anglia (HadCRUT) – because it uses many more station records.
The BEST team also use a different statistical method to calculate the average land temperature record from the methods used by NOAA, GISS and HadCRUT. The team boasts that its approach is simple, pointing out that it doesn’t rely on complicated climate models.
The attribution of much of the last 50 years’ warming to human activity is in line with several recent studies using a variety of sophisticated approaches to calculate the contributions of natural and human causes of global warming. The studies agree that human activity is the dominant cause of warming over the last century, and particularly over the last 50 years.
Is the BEST research peer reviewed?
This new research is not yet peer reviewed. The BEST team explains why:
“Some people think that peer review consists of submitting a paper to a journal and waiting for the anonymous comments of referees. Traditional peer review is much broader than that and much more open. In science, when you have a new result, your first step is to present it to your colleagues […] Such traditional and open peer review has many advantages. It usually results in better papers in the archival journals, because the papers are widely examined prior to publication. It does have a disadvantage, however, that journalists can also pick up preprints and report on them before the traditional peer-review process is finished.”
When the BEST team last released papers they were also non-peer-reviewed preprints. Those papers have since been submitted to peer-reviewed journals. Only one out of those four, however, appears to have been accepted for publication so far, according to the BEST website.
The peer review process allows independent qualified experts to scrutinise scientific methods, results and interpretations before they are made public. It provides a kind of stamp of approval for new research, in that it shows that the research is considered valid, significant and original by experts in the field. So the fact that any BEST research has attracted so much media attention before even being peer reviewed is a little worrying – the research could turn out to be good, but could also turn out to be flawed or incomplete.
How much does the BEST study matter?
“[The BEST team has] done none of the attribution work you’d expect, in order to talk about attribution. And what they say […] appears absurdly naive.”
Climate scientist Ken Caldeira points out:
“The basic scientific results have been established for a long time now, so I do not see the results of Muller et al as being scientifically important. However, their result may be politically important. It shows that even people who suspect climate scientists of being charlatans, when they take a hard look at the data, see that the climate scientists have been right all along.”
BEST member Curry describes its temperature record as “the best land surface temperature data set that we currently have”, but declined to be a co-author on the latest paper, since she disagrees with its interpretation attributing the temperature rise to atmospheric carbon dioxide.
What about the Watts et al. paper?
Coinciding with the release of the latest BEST team results comes news from climate skeptic weatherman and blogger Anthony Watts. Watts and colleagues have released new, yet-to-be-peer-reviewed research into where US weather stations are sited, and whether this affects the average US temperature trend.
Watts has long blogged about the siting of weather stations, and in 2011 co-authored a paper on the topic which concluded that poorly sited US weather stations gave biased temperature readings – either artificially hot and artificially cold – but that these balanced each other out, not affecting the overall temperature trend.
Watts and colleagues’ hastily produced new paper – he apparently released it at the same time as the BEST study deliberately – seems to revoke his previous conclusions. He now suggests that:
“U.S. Temperature trends show a spurious doubling due to NOAA station siting problems and post measurement adjustments.”
Roger Pielke Sr. – acknowledged in the paper from Watts and colleagues for his help in its production – decribes the new research as “seminal”. But the research has come under criticism from climate scientist Victor Venema, University of Bonn, and is at odds with recent research.
Despite all the publicity, neither of these papers have received the important stamp of approval from the rest of the scientific community that constitutes peer-review. Will they make it through the peer review process? We’ll have to wait and see, but until they’ve been reviewed by specialists, it’s difficult to assess how scientifically significant they are.
Updated 10:48 01/08/12 to reflect Roger Pielke Sr.’s involvement with the paper by Watts and colleagues.