Retre­at of Arc­tic sea ice acce­le­ra­tes glo­bal warm­ing

The retre­at of Arc­tic sea ice acts as an acce­le­ra­tor for cli­ma­te chan­ge, sin­ce the bright ice sur­faces reflect much more sun­light than the dar­ker sur­faces of open water. Ice reflects up to 90% of solar ener­gy back to space while water absorbs a lar­ge amount of ener­gy and warms both its­elf and the over­ly­ing air lay­ers.

If warm­ing leads to retrea­ting ice, then this effect cau­ses addi­tio­nal warm­ing and the ice melts even fas­ter: a clas­si­cal posi­ti­ve feed­back reac­tion. Of cour­se this would also work the other way around: If lower tem­pe­ra­tures cau­se an expan­si­on of snow and ice cover­ed are­as, this would lead to an addi­tio­nal coo­ling.

The abili­ty of sur­faces to reflect radia­ti­on is expres­sed by the albe­do, a figu­re that quan­ti­fies the amount of reflec­ted radia­ti­on in per­cent.

Sci­en­tists of the Uni­ver­si­ty of Cali­for­nia in San Die­go could now, by satel­li­te mea­su­ring, veri­fy that the albe­do north of the 60. degree of lati­tu­de is fal­ling and that this is rela­ted to the retre­at of arc­tic sea ice. The result of the mea­su­re­ments is that the albe­do decreased from 0,52 to 0,48 bet­ween 1979 and 2011. Ins­tead of 52% now only 48% of the solar radia­ti­on in the Arc­tic is reflec­ted. This cor­re­sponds to an addi­tio­nal avera­ge input of solar ener­gy of ca. 6,4 W/m² sin­ce 1979. Aver­a­ged over the glo­be this cor­re­sponds to an addi­tio­nal ener­gy input of 0,21 W/m², which is 25% of the amount attri­bu­ted to the increase of CO2 in the same peri­od.

The­se figu­res are signi­fi­cant­ly hig­her than tho­se expec­ted befo­re by models and esti­ma­tes.

Ano­ther result of the mea­su­ring is the fact that the albe­do also decreased in are­as which were cover­ed with ice all over the year. One expl­ana­ti­on for this is an incre­asing occur­rence of melt water lakes on the ice which again absorb more solar ener­gy and cau­se addi­tio­nal warm­ing.

Sources: Spie­gel Online Wis­sen­schaft, Pro­cee­dings of the Natio­nal Aca­de­my of Sci­en­ces of the United Sta­tes of Ame­ri­ca (PNAS)

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