Researchers say that monthly temperature extremes have become much more frequent as measurements from around the world indicate, and on an 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 even by a factor of 10.
80 percent of observed monthly records would not have occurred without human influence on climate, concludes the authors-team of the Potsdam Institute for Climate Impact Research (PIK) and the Complutense University of Madrid.
Record-breaking hot months have become much more frequent. (For full graphic see Fig. 4 in the study) Graphic: PIK
"The last decade brought unprecedented heat waves; for instance in the US in 2012, in Russia in 2010, in Australia in 2009, and in Europe in 2003," lead-author Dim Coumou said.
"Heat extremes are causing many deaths, major forest fires, and harvest losses - societies and ecosystems are not adapted to ever new record-breaking temperatures," Coumou said.
The new 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 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 Nino events.
This natural variability, however, does not explain the overall development of record events, found the researchers.
Natural variability 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," Coumou said.
For the new records set in the 2040s will not just be hot by today's standards.
"To count as new records, they actually have to beat heat records set in the 2020s and 2030s, which will already be hotter than anything we have experienced to date," Coumou said.
"And this is just the global average - in some continental regions, the increase in new records will be even greater," Coumou added.
The study has been published in Climatic Change.