Thin cloud cover linked to arctic ice melt and sea-level rise

An analysis of the Greenland ice cap says that global sea levels would rise 24 feet if the entire sheet melted.

That number suggested by University of Wisconsin-Madison researchers is very close to the sea level that actually existed during the last interglacial, according to earlier figures from Woods Hole Oceanographic Institution.

The most recent assessment said that researchers have been tracking increasing melt rates in Greenland since at least 1979. Last summer, however, the melt was so large that similar events show up in ice core records only once every 150 years or so over the last four millennia, the research team  said..

A paper scheduled for publication today said the unusual surface melting was triggered by an influx of unusually warm air, but that was only one factor, said Dave Turner, physical scientist at the National Oceanic and Atmospheric Administration’s National Severe Storms Laboratory. “In our paper we show that low-level clouds were instrumental in pushing temperatures up above freezing.”

Low-level clouds typically reflect solar energy back into space, and snow cover also tends to bounce energy from the sun back from the Earth’s surface.

Under particular temperature conditions, however, clouds can be both thin enough to allow solar energy to pass through to the
surface and thick enough to trap some of that heat even if it is turned back by snow and ice on the ground.

While low, thin cloud cover is just one element within a complex interaction of wind speed, turbulence and humidity, the extra heat energy trapped close to the surface can push temperatures above freezing, the paper said.

Many scientists expect the sea level to rise about a foot per century due to the increase in global temperature. Some think that this rate can be reduced by human efforts to reduce carbon dioxide emissions into the atmosphere.

Still, the rate presents serious problems for island nations and coastal areas of Costa Rica where higher sea levels can cause more inundations. An example is the sandy peninsula on which Puntarenas Centro sits. The Instituto Meteorológico Nacional already had calculated the loss of dry land that would accompany sea level rises of varying degrees.

However, there have been no calculations that take into account a sea level rise of 24 feet. Three million cubic kilometers of Greenland ice won’t wash into the ocean overnight, the University of Wisconsin researchers said. But evidence of sea-level oscillations during a warm period that started about 125,000 years ago raises the possibility of a similar scenario if the planet continues its more recent warming trend, says the research team at the Woods Hole Oceanographic Institution.

They suggested the possibility of sea-level changes that are more dynamic than current observations of ice sheets suggest.

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