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Don Paul: Worrisome melting on Antarctica will add to rising sea levels

Climate models correctly predicted back in the 1980s that warming would be greatest and fastest in the Arctic.

Some of the physics in that forecast were simple. As Arctic sea ice melted more quickly during summer months, surface reflectivity of solar energy would change more drastically than anywhere else on the planet. The bright white ice and snow cover reflect much of the solar energy reaching the surface back up into space, keeping the surface colder. As greater expanses of dark blue sea water increased, that reflectivity known as albedo, has been greatly reduced. The dark waters, rather than reflecting solar energy became a heat sink, absorbing more of the sun’s heat.

This process of changing albedo becomes a feedback mechanism. With warmth absorbed into the Arctic Ocean, the water warms and expands (warmer water expands) and doesn’t freeze to as thick a coating of ice as had been the case before this warming had become ongoing.

The warming of the Arctic has also led to increased melting of the permafrost in the tundra, and more rapid ice melt from Greenland. Arctic sea ice melt doesn’t directly cause sea levels to rise, anymore than a melting ice cube in your drink causes the level of liquid in your glass to rise. However, ice melt has accelerated on the vast ice cap of Greenland. That melt water does indeed cause sea level rise, along with lesser contributions from glacier melt on the continents.

(NASA image)

Antarctica has been a different story. As the 1980s models predicted, melting has been much slower than in the Arctic because the large majority of Antarctic ice lies on a vast continent, rather than the ocean. In its interior, there has been no melting down to a dark surface with a lower albedo. Therefore, the feedback mechanism for accelerated melting on the interior of Antarctica is absent as well. At times, snow and ice have actually gained mass closer to the South Pole during the era of melting.

[Washington Post vido: Flowing water on surface of Antarctica has scientists worried]

If you play the :06 second video in this Washington Post article, you’ll see what has never been observed before. Last year, a remote camera recorded a waterfall at the surface on the Ross Ice Shelf in Antarctica. Until recently, it was thought Antarctic ice melt occurred mainly where the the ice shelf met the sea, and that is primarily on the bottom of the ice. The Ross Ice Shelf, on West Antarctica extends off the land mass, and it’s melting at differing rates each year.

Were the shelf to melt in its entirety, it would raise sea levels by a catastrophic 10 feet. The Ross Ice Shelf covers an area larger than Texas. It is thought last year’s extraordinarily major el nino provided enough warmth to not only dramatically increase melt rates, but also brought more water vapor to produce significant rainfall over that shelf, which is almost unprecedented.

Here are surface ice melt days at the surface, in an image provided by Julien Nicholas of the Scripps Institute of Oceanography:

Ssurface ice melt days at the surface, in an image provided by Julien Nicholas of the Scripps Institute of Oceanography.

The el nino melting hypothesis is only a hypothesis, since the powerful warm 1997-98 el nino event did not produce such melting on the surface of Antarctic Ross Ice Shelf.

Satellite imagery from polar orbiting satellites showed large pools of water, some truly like large lakes, as well as huge areas of watery slush. Rain extending into the interior of Antarctica over such an expansive region is also close to unprecedented, since Antarctica is actually quite arid — a desert by climatological classification.

In any case, accelerated melting of the shelf occurs when there is liquid sitting on its top as well as warming ocean waters lapping at its bottom. The Ross Ice Shelf and other shelves hold back vast glaciers in the interior. The reduction of these shelves would allow more rapid melting of those glaciers, accelerating the overall amount of fresh water meltoff reaching the ocean. A recent study in the Journal of Nature estimates sea level rises of 4 feet could occur just in this century with these ongoing processes in Antarctica.

Don Paul: There's nothing simple about rising sea levels

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