Environment

A physicist whose work is often highlighted by climate-change sceptics is refusing to provide the software he used to other climate researchers attempting to replicate his results.

Nicola Scafetta, a physicist at Duke University in Durham, North Carolina, has published a series of papers over the past few years that suggest the sun played a much bigger role in warming over the 20th century than is generally accepted. In particular, one 2006 paper he co-authored concluded that: "The sun might have contributed approximately 50 per cent of the observed global warming since 1900" (Geophysical Research Letters, DOI: 10.1029/2006GL027142).

This paper has been widely cited by those seeking to cast doubt on the scientific consensus on the cause of climate change, including US senator James Inhofe. Scafetta has also contributed to a book that claimed that "carbon dioxide probably is not the driving factor behind climate change".

Many researchers in the field (PDF), however, regard Scafetta's scientific papers on the sun's role in global warming as incorrect, despite their publication in peer-reviewed journals.

Playing down the sun

Earlier this year, for instance, Rasmus Benestad of the Norwegian Meteorological Institute in Oslo and Gavin Schmidt of NASAs Goddard Institute for Space Studies in New York published a paper claiming that Scafetta's methodology produces larger errors than he acknowledges. Benestad and Schmidt concluded that the sun is responsible for only about 7 per cent of the warming in the 20th century and none after 1980.

Scafetta claims Benestad and Schmidt have made many errors of their own. However, he is now refusing to give them the program code he used to allow them to try to replicate his results.

New Scientist was copied in on a series of emails between Benestad and Scafetta over the past week, in which Scaffetta repeatedly refused to provide the code. "If you just disclose your code and data, then we will manage to get to the bottom of this," Benestad writes in one email. "I really do not understand why you are not able to write your own program to reproduce the calculations," responds Scafetta.

In response to direct questions from New Scientist, Scafetta said the code in question had been submitted to a scientific journal and that if "the journal takes its time to publish it, it is not our fault". Benestad says the code he is asking for relates to papers already published.

Show us your code

Some of those questioning the scientific consensus on climate change have long demanded that climate scientists release all their data and code, an issue that has come to the fore following the "Climategate" affair. Some climate scientists reject such calls, in part because the data and code relating to published studies can have commercial value.

Many others, however, welcome the idea because it will make research much easier. Back in 2003, Michael Mann, now at Penn State University in University Park, initially refused to make available the data and code relating to the "hockey stick" graph. Now he is releasing all the data and code relating to his papers.

Researchers like Benestad say the demand for more open access and increased transparency should also apply to researchers who question the scientific consensus, making it far quicker and easier to settle debates about errors in papers.

Inhofe's office continues to highlight Mann's initial refusal to release his data and code. It remains to be seen whether the senator will join those calling for Scafetta to release his code.

Read more: New Scientist's full coverage of the latest Copenhagen and climate change news

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