Human influence on climate tied to increase in monthly heat records

January 14th, 2013 by Potsdam Institute for Climate Impact Research

A heat wave and fires in Basom, New York (click image to expand - image courtesy of Catherine J. Hibbard, US Fish Wildlife Service)

Temperature measurements from around the world indicate that monthly temperature extremes have become much more frequent.

A study published in the paper ‘Global increase in record-breaking monthly-mean temperatures‘ in the journal Climatic Change shows that, on average, there are now five times as many record-breaking hot months worldwide than could be expected without long-term global warming.

In parts of Europe, Africa, and southern Asia the number of monthly records has increased ten-fold.

According to the authors from the Potsdam Institute for Climate Impact Research (PIK) and the Universidad Complutense de Madrid, 80% of observed monthly records would not have occurred without human influence on climate.

Dim Coumou, lead author of the paper, said “the last decade brought unprecedented heat waves; in Europe in 2003, in Australia in 2009, in Russia in 2010, and in the US in 2012.

“Heat extremes are causing many deaths, major forest fires, and harvest losses – societies and ecosystems are not adapted to ever new record-breaking temperatures.”

This study relies on 131 years of monthly temperature data for more than 12,000 grid points around the world provided by NASA

Comprehensive analysis reveals the increase in record-breaking temperature records.

The researchers developed a robust statistical model that explains the surge in the number of records to be a consequence of the long-term global warming trend.

That surge has been particularly steep over the last 40 years, due to a steep global-warming trend over this period.

Superimposed on this long-term rise, the data show the effect of natural variability, with especially high numbers of heat records during years with El Niño events.

The researchers found that this natural variability, however, does not explain the overall development of record events.

If global warming continues, the study projects that the number of new monthly records will be 12 times as high in 30 years as it would be without climate change.

“Now this doesn’t mean there will be 12 times more hot summers in Europe than today – it actually is worse,” Dr Coumou said.

For the new records set in the 2040’s will not just be hot by today’s standards.

“To count as new records, they actually have to beat heat records set in the 2020’s and 2030’s, which will already be hotter than anything we have experienced to date,” Dr Coumou said.

“And this is just the global average – in some continental regions, the increase in new records will be even greater.”

Professor Stefan Rahmstorf, a co-author of the study and co-chair of PIK’s research domain Earth System Analysis, said “statistics alone cannot tell us what the cause of any single heat wave is, but they show a large and systematic increase in the number of heat records due to global warming.”

“Today this increase is already so large that by far most monthly heat records are due to climate change.”

“The science is clear that only a small fraction would have occurred naturally,” he said.


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