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Global warming probably causing heat waves, study says

Aug. 5, 2012
Courtesy of PNAS
and World Science staff

Re­cent heat waves and ex­treme sum­mers were likely caused by glob­al warm­ing, a study re­ports. 

James Han­sen of NASA’s God­dard In­sti­tute for Space Stud­ies and col­leagues ex­am­ined the role of glob­al warm­ing in re­cent high pro­file heat waves, such as those in Tex­as and Ok­la­ho­ma in the sum­mer of 2011 and in Mos­cow in 2010. 

The re­search­ers com­pared re­cent June, Ju­ly, and Au­gust sur­face tem­per­a­ture anoma­lies rel­a­tive to 1951-1980. They found that ex­tremely hot sum­mers oc­curred much more often in the past sev­er­al years than dur­ing the ear­li­er pe­ri­od, when they were prac­tic­ally ab­sent.

The ex­tremely hot sum­mers have af­fect­ed an es­ti­mat­ed 10 per­cent of glob­al land ar­ea in re­cent years, com­pared with less than 1 per­cent of the Earth’s sur­face dur­ing the ear­li­er pe­ri­od, Han­sen and col­leagues said. The study con­cludes that the re­cent ex­treme sum­mer cli­mate anoma­lies would likely not have oc­curred with­out glob­al warm­ing, which sci­en­tists blame on heat-trapping car­bon di­ox­ide and oth­er gas­es re­leased in­to the at­mos­phere by hu­man ac­ti­vity.

Con­tin­ued warm­ing could po­ten­tially make ex­tremely hot sum­mers the norm and pos­sibly con­trib­ute to ex­treme droughts and floods, ac­cord­ing to the sci­en­tists. The study is pub­lished in this week’s early on­line edi­tion of the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces.

“The cli­mate di­ce are now load­ed to a de­gree that a per­cep­tive per­son old enough to re­mem­ber the cli­mate of 1951–1980 should rec­og­nize the ex­ist­ence of cli­mate change, es­pe­cially in sum­mer,” Han­sen and col­leagues wrote.

“Changes of glob­al tem­per­a­ture are likely to have their great­est prac­tical im­pact via ef­fects on the wa­ter cy­cle,” they added. “With the tem­per­a­ture am­pli­fied by glob­al warm­ing and ubiq­ui­tous sur­face heat­ing from el­e­vat­ed green­house gas amounts, ex­treme drought con­di­tions can de­vel­op… The oth­er ex­treme of the wa­ter cy­cle, un­usu­ally heavy rain­fall and floods, is al­so am­pli­fied by glob­al warm­ing.”

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Recent heat waves and extreme summers were likely caused by global warming, a study reports. James Hansen of NASA’s Goddard Institute for Space Studies and colleagues examined the role of global warming in recent high profile heat waves, such as those in Texas and Oklahoma in the summer of 2011 and in Moscow in 2010. The researchers compared recent June, July, and August surface temperature anomalies relative to 1951-1980. They found that extremely hot summers occurred much more frequently in the past several years than during the earlier period, when they were practically absent. The extremely hot summers have affected an estimated 10% of global land area in recent years, compared with less than 1% of the Earth’s surface during the earlier period, Hansen and colleagues said. The study concludes that the recent extreme summer climate anomalies would likely not have occurred without global warming, which scientists blame on heat-trapping carbon dioxide and other gases released into the atmosphere by human activity. Continued warming could potentially make extremely hot summers the norm and possibly contribute to extreme droughts and floods, according to the scientists. The study is published in this week’s early online edition of the research journal PNAS. “The climate dice are now loaded to a degree that a perceptive person old enough to remember the climate of 1951–1980 should recognize the existence of climate change, especially in summer,” Hansen and colleagues wrote. “Changes of global temperature are likely to have their greatest practical impact via effects on the water cycle,” they added. “With the temperature amplified by global warming and ubiquitous surface heating from elevated greenhouse gas amounts, extreme drought conditions can develop… The other extreme of the water cycle, unusually heavy rainfall and floods, is also amplified by global warming.”