Sceptical climate scientists concede Earth has warmed

A group of scientists known for their scepticism about climate change has reanalysed two centuries' worth of global temperature records. Their study largely confirms previous ones: it finds strong evidence that Earth is getting hotter.

"The valid issues raised by [climate] sceptics, when addressed fully and in detail, do not significantly change the answer," says lead author Richard Muller of the University of California, Berkeley. In a testimony to the US Congress earlier this year, Muller questioned whether global temperature records showed a significant warming during the 20th century.

His project, the Berkeley Earth Surface Temperature (BEST), has now pulled together global temperature data going back to 1800 from 15 sources, including datasets held by the World Meteorological Organisation and US and UK government agencies.

BEST concludes that land temperatures have risen by 1??C since the 1950s. This is largely in line with the three existing global temperature records: GISTEMP, maintained by NASA, the US National Oceanic and Atmospheric Administration's GHCN and HadCRU, kept by the UK Met Office. The 1??C of warming reflects warming above land masses only, so is not yet a truly global estimate.

In a series of papers that have not yet been peer-reviewed but are available on the BEST website, the researchers examine how reliable the temperature data is.

Contrary to earlier studies that are often quoted by climate sceptics, the BEST researchers find that including data from weather stations in cities ? which are warmer than rural areas ? makes little difference to the overall trend. "Urban warming does not unduly bias estimates of recent global temperature change," they say.

Blogger Anthony Watts of Watts Up With That has repeatedly claimed that temperature data is unreliable because weather stations are poorly placed ? for instance, next to air-conditioning vents or other heat sources. However, BEST found no statistically significant difference in the trends seen at well-placed and poorly placed stations.

No surprise

"These initial findings are very encouraging and echo our own results, and our conclusion that the impact of urban heat islands on the overall global temperature is minimal," says Phil Jones of the University of East Anglia in Norwich, UK, the climatologist at the heart of the "climategate" scandal. Jones helped to compile the HadCRU dataset.

"They get the same result that everyone else has gotten," says Michael Mann of Penn State University in University Park. "That said, I think it's at least useful to see that even a critic like Muller, when he takes an honest look, finds that climate science is robust."

The UK Met Office refused to comment on the studies because they have not been through peer review. Other climate scientists expressed similar reservations.

Muller defended the decision to circulate the results before publication, saying he was going through peer review "in the traditional way: by circulating preprints and giving seminars and talks".

The blogosphere responds

Prominent critics of climate science contacted by New Scientist say the temperature record is not at issue.

"I haven't ever suggested that temperatures haven't risen since the 19th century. Quite the contrary," says blogger and mathematician Steve McIntyre of ClimateAudit. Nevertheless, McIntyre questions BEST's analyses of urban heating and weather station quality.

"They're concentrating on the wrong question," says David Whitehouse, science adviser to The Global Warming Policy Foundation, a London-based think tank that has former British finance minister Nigel Lawson for chairman. "Everybody agrees that the temperature has warmed. The people who disagree about temperatures are the barking mad end of the spectrum."

He claims the uncertainty lies in the size of the human effect on the climate, as compared to natural effects (see "Climate myths: Human CO₂ emissions are too tiny to matter").

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