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August 03, 2010

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Nuke exchange would shred ozone layer: study

Urban fires seen spreading damage

April 7, 2008
Courtesy PNAS
and World Science staff

A re­gion­al nu­clear ex­change could wipe out most of the Earth’s pro­tect­ive ozone lay­er, re­search­ers re­port. The lay­er is a part of the at­mos­phere that con­tains enough ozone to block most of the sun’s ul­tra­vi­o­let radia­t­ion, which burns the skin and can cause skin can­cer.

An atomic bomb tested on June 24, 1957 in Ne­vada. (Im­age cour­te­sy State of Ne­va­da) 
Mi­chael Mills of the Uni­ver­s­ity of Col­o­rado, Boul­der, and col­leagues con­clud­ed from sim­ula­t­ions that a con­flict in­volv­ing the ex­change of 100 Hiroshima-equivalent bombs would cause ur­ban fires whose smoke would dec­i­mate the ozone lay­er. 

The fires would loft as much as five mil­lion met­ric tonnes of soot in­to the trop­o­sphere, the low­est at­mos­pher­ic lay­er, the re­search­ers ar­gued. So­lar heat­ing, they added, would then boost the soot in­to the strat­o­sphere, a high­er lay­er.

Up to about 60 km (40 miles) high the soot would ab­sorb so­lar radia­t­ion and heat the sur­round­ing gas­es, thus speed­ing up chem­i­cal re­ac­tions that break down ozone, the sci­en­tists said.

They used a mod­el that linked cli­mate to at­mos­pher­ic chem­is­try to con­duct 10-year sim­ula­t­ions. Their mod­el pre­dicts that in a nu­clear con­flict be­tween In­dia and Pa­ki­stan, at­mos­pher­ic cur­rents would likely spread soot around the globe, re­sult­ing in lo­cal at­mos­pher­ic warm­ing of up to 30-60 de­grees Cel­si­us. 

Some ozone-destroying re­ac­tions would ac­cel­er­ate at the high­er tem­per­a­tures, the re­search­ers con­tin­ued. In both hemi­spheres, they ad­dded, the ozone from 20 de­grees north or south lat­i­tude to the poles would thin be­low the thresh­old de­fin­ing a cur­rently ex­ist­ing Ant­arc­tic ozone hole. The mod­el pre­dicts that the at­mos­phere would beg­in to re­cov­er in five to eight years. 

The study is to ap­pear in this week’s early on­line edi­tion of the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces.

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A regional nuclear exchange would create a nearly Earth-sized hole in the ozone layer, researchers report. The ozone layer is a part of the atmosphere that contains enough ozone to block most of the sun’s dangerous ultraviolet radiation. Michael Mills of the University of Colorado, Boulder, and colleagues concluded from simulations that a conflict involving the exchange of 100 Hiroshima-equivalent bombs would cause urban fires whose smoke would decimate the ozone layer. The fires would loft as much as five million metric tonnes of soot into the troposphere, the lowest atmospheric layer, the researchers argued. Solar heating, they added, would then boost the soot into the stratosphere, a higher layer. At altitudes up to about 60 km (40 miles) the soot would absorb solar radiation and heat surrounding gases, thus increasing the rate of chemical reactions that break down ozone, the scientists said. They used a model that linked climate to atmospheric chemistry to conduct 10-year simulations. Their model predicts that in a hypothetical nuclear attack between India and Pakistan, atmospheric currents would likely distribute soot around the globe, resulting in local atmospheric warming of up to 30-60 degrees Celsius. Some ozone-destroying reactions would accelerate at the higher temperatures, the researchers continued. In both hemispheres, they addded, the ozone from 20 degrees north or south latitude to the poles would thin below the threshold defining a currently existing Antarctic ozone hole. The model predicts that the atmosphere would begin to recover in five to eight years. The study is to appear in this week’s early online edition of the research journal pnas.