Tuesday, March 20, 2012

Perfect storm erupts over new climate data

Jo Chandler 
The Age, March 21, 2012   

THE update of a 160-year-old global temperature record by British scientists, plugging in additional data collected primarily across the Arctic, has resulted in 2010 now being ranked as the warmest year on record, followed by 2005, and bumping the previously top-ranked El Nino super-heated 1998 to third place.

In terms of scientific significance, it's not a big deal, the experts say - ''it makes essentially no difference to the assessment of trends over the last 100 years'', says Dr Blair Trewin, a climatologist at the National Climate Centre of the Bureau of Meteorology. It also falls in line with the other two principle global temperature records - both compiled in the United States.

But in terms of public discussion about climate change, the update has stirred up a disproportionate storm. The peak ranking of 1998 in the British data set was frequently cited by people arguing against the scientific consensus of human-induced global warming as evidence that temperatures had not risen in 14 years.

The British HadCRUT record is compiled by the British Met Office's Hadley Centre and the Climatic Research Unit at the University of East Anglia. The integrity of the record was caught up in the so-called ''Climategate'' affair in 2009, which circulated hacked emails from CRU scientists. Concerns about the content of the emails provoked at least eight separate inquiries by British and US government agencies, independent panels and universities. None identified wrongdoing by the scientists - although they were criticised for failing to share information - and the science was unassailed.

In some ways - in particular in regard to its approach to extrapolating data over distance - the British record is regarded as the most conservative of the records, Dr Trewin said.

The update draws on additional temperature records to redress ''holes in the [real-time] data over Russia and to an extent Canada. And because the last decade has been particularly warm at high latitudes, that pushes up the overall global averages,'' Dr Trewin said.

''They've also done a much more rigorous job of merging different types of data [from sources including sea-surface buoys as well as ships and satellites] which have all got their own biases and uncertainties.

''As a result, 1998 [which came on the back of a strong El Nino] no longer stands out as being a big outlier in the temperature record, as it was.''

''The inclusion of data from the Arctic gives better global coverage and better agreement with satellite data and other global surface temperature data sets for the observed global warming over the last 30 years and the last decade,'' said Professor David Karoly, a climate expert from the University of Melbourne.

Changes in global temperature estimates in individual years are not statistically significant, he said. But ''the global climate system is still warming and these new data provide additional evidence confirming that''.

The adjustment to the British data will likely later be reflected in the central collated temperature record, maintained by the World Meteorological Organisation, when the full data set is released. It will be publicly available online shortly.

No comments: