Greenland ice sheet softening like butter.Scientists have been puzzling out the exact mechanisms for

Greenland ice sheet softening like butter.Scientists have been puzzling out the exact mechanisms for the accelerating glacier surges flowing off the Greenland ice sheet as it continues to melt at an unprecedented rate in the face of climate change. These surges drain ice off the cap into the sea contributing to sea level rise. As the surface melts, lakes and rivers form on the ice, eventually draining into the ice sheet through holes known as moulins or by the phenomenon of ice lake drainage captured in the documentary Chasing Ice. Scientists already suspect that this water is lubricating the bottom of the sheet, lifting it off the bedrock and causing the surges.A study published by the American Geophysical Union has shown that the deep interiors of the sheet are also surging much faster than a decade ago, and proposes that the cause is the relative warmth of the draining water from the surface melt. This sun heated water warms the deep ice from the inside and softens it, allowing it to flow faster. Warm water carries an immense amount of latent heat, and it is well known that the oceans have absorbed much more of the extra heat energy from climate change than the atmosphere.Researchers used satellite images to quantify the movement of ice deep inland, and determined that it is moving at 1.5 times the speed of a decade ago (from 40 to 60 metres yearly). This worrying fact shows that the surging is not just happening towards the glacial snouts as they get into the warmer air closer to sea level, but deeper in the ice cap, suggesting that further downstream acceleration is likely.Surging so deep in the ice cap is not related to what happens as it enters the sea, but must be related to a change in the deep ice. The team modelled the effect of the warm water entering the sheet from the surface and found that the result was a close approximation of observed reality, with the iuce softening and flowing like warmed butter under its own weight. This suggests that our current models are underestimating the likely future contribution this ice cap will make to sea level rise in our warming world. Earlier models essentially inputted the sheet as a giant ice cube, without taking account of the fact that surface melt water is turning it into something more akin to Swiss cheese.The model showed that only a couple of degrees Celsius is sufficient to produce this effect, making for disturbing thoughts when one ponders that the current estimates give us 3-6 degrees of warming by 2100. The rise in sea level may well come much faster than we hope, constraining the time that society has to respond to the challenge of evacuating so much low lying land, including many of the world’s great cities.LozImage credit: J. Boxhttp://www.agu.org/news/press/pr_archives/2013/2013-35.shtml -- source link

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