A faster timetable for ris­ing seas?

Melt­wa­ter pools may speed the threat to Antarc­tica’s ice shelves.

The Washington Post Sunday - - SUNDAY OPINION -

YOU’VE HEARD THIS one be­fore: The Earth is com­plex and con­stantly chang­ing, so how can sci­en­tists pos­si­bly know that burn­ing fos­sil fu­els will do so much harm to the planet? This ar­gu­ment has never been per­sua­sive. It is no mys­tery that adding heat-trap­ping gases to the at­mos­phere will trap more heat. That some un­cer­tain­ties re­main does not nec­es­sar­ily fa­vor the doubters: Things could be worse than ex­pected — not just bet­ter.

Two new pa­pers on how melt­wa­ter flows on the sur­face of Antarc­tica’s vast icy ex­panse drive this es­sen­tial point home. There is an as­ton­ish­ing amount of wa­ter frozen on top of the south­ern con­ti­nent, hemmed in by float­ing ice shelves abut­ting the Antarc­tic land mass. For now, that is: A ma­jor ice shelf dis­in­te­grated in 2002, and sci­en­tists just re­ported an omi­nous new crack in an­other close by. Los­ing ice shelves en­cour­ages the ice fur­ther back to melt and drain into the ocean, raising the seas to dan­ger­ous lev­els. A ma­jor threat to these ice shelves is melt­wa­ter that pools on the sur­face, widen­ing cracks and en­cour­ag­ing them to break up. Sci­en­tists have known about this threat for years, yet they still do not know much about Antarc­tica’s “plumb­ing.”

A team from Columbia Univer­sity and the Univer­sity of Sh­effield that ex­am­ined decades of satel­lite mon­i­tor­ing and aerial pho­to­graphs found vast net­works of melt­wa­ter-fed streams and lakes across Antarc­tica. The streams can flow for up to 75 miles be­fore reach­ing melt ponds or the sea. Melt ponds, mean­while, can be mas­sive — up to 50 miles long. If this sys­tem de­liv­ers in­creas­ing amounts of wa­ter to the wrong parts of del­i­cate ice shelves, it could se­verely dam­age them.

As the tem­per­a­ture rises, more melt­wa­ter will flow into this hy­dro­log­i­cal sys­tem, and the sci­en­tists warn that the re­gion might en­ter a dev­as­tat­ing feed­back loop. As more ice melts around the con­ti­nent, more rocks and other non­white fea­tures of the land­scape are ex­posed. These darker fea­tures ab­sorb more of the sun’s heat. This en­cour­ages melt­ing. The re­sult­ing melt­wa­ter could then en­cour­age ice shelves to de­cline, which could en­cour­age fur­ther thin­ning far­ther back on the con­ti­nent, and there­fore fur­ther ex­po­sure of heat-ab­sorb­ing rocks.

Even so, it is not clear ev­ery ice shelf is in crit­i­cal dan­ger. In an­other pa­per, the sci­en­tists dis­cussed a drainage sys­tem in one part of Antarc­tica that di­verted melt­wa­ter di­rectly into the ocean, ap­par­ently with­out un­der­min­ing sen­si­tive parts of the ice shelf over which it flowed. Rather than un­der­min­ing the sta­bil­ity of the ice, the flow ap­pears to be bol­ster­ing it.

It will take years more re­search for sci­en­tists to bet­ter ac­count for Antarc­tic melt­wa­ter in cli­mate mod­els. But it would be fool­hardy to as­sume that it will all harm­lessly drain into the ocean. Bet­ter to take the warn­ing: Dra­mat­i­cally higher sea lev­els may come sooner than we think.

Newspapers in English

Newspapers from USA

© PressReader. All rights reserved.