GLOBAL WARMING

Antarctic ice melting from warm water

7:36 AM Thursday Apr 26, 2012 NZ Herald

Antarctica's massive ice shelves are shrinking because they are being eaten away from below by warm water, a new study finds. That suggests that future sea levels could rise faster than many scientists have been predicting.

The western chunk of Antarctica is losing 7 metres of its floating ice sheet each year. Until now, scientists were not exactly sure how it was happening and whether or how man-made global warming might be a factor. The answer, according to a study published in the journal Nature, is that climate change plays an indirect role - but one that has larger repercussions than if Antarctic ice merely were melting from warmer air.

Hamish Pritchard, a glaciologist at the British Antarctic Survey, said research using an ice-gazing NASA satellite showed that warmer air alone could not explain what was happening to Antarctica. A more detailed examination found a chain of events that explained the shrinking ice shelves.

Twenty ice shelves showed signs that they were melting from warm water below. Changes in wind currents pushed that relatively warmer water closer to and beneath the floating ice shelves. The wind change probably is caused by a combination of factors, including natural weather variation, the ozone hole and man-made greenhouse gases, Pritchard said in a phone interview.

As the floating ice shelves melt and thin, that in turn triggers snow and ice on land glaciers to slide down to the floating shelves and eventually into the sea, causing sea level rise, Pritchard said. Thicker floating ice shelves usually keep much of the land snow and ice from shedding to sea, but that is not happening now.

That whole process causes larger and faster sea level rise than simply warmer air melting snow on land-locked glaciers, Pritchard said.

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"It means the ice sheets are highly sensitive to relatively subtle changes in climate through the effects of the wind," he said.

What's happening in Antarctica "may have already triggered a period of unstable glacier retreat," the study concludes. If the entire Western Antarctic Ice Sheet were to melt, which would take many decades if not centuries, scientists have estimated it would lift global sea levels by about 3 metres.

NASA chief scientist Waleed Abdalati, an expert in Earth's ice systems who was not involved in the research, said Pritchard's study "makes an important advance" and provides crucial information about how Antarctica will contribute to global sea level rise.

Another outside expert, Ted Scambos of the National Snow and Ice Data Center, said the paper will change the way scientists think about melt in Antarctica. Seeing more warm water encircling the continent, he worries that with "a further push from the wind" newer areas could start shrinking.

Peter’s Comment

So now we have another point of view which leads us to believe that the melting of the polar ice caps is not just hot air.

The polar ice caps weigh trillions of tons and, like a moving ship weighing thousands of tons, it takes a long time and a great deal of space to turn them around. The polar ice caps may have been melting since the last warm age in the fifteenth century when there was almost no industrial activity to blame.

Furthermore, sea-levels and coastlines have been changing, not just throughout recorded history, but even before man walked the planet. Sea-levels have changed not just by three metres, but by thousands of metres and even whole continents have come and gone and will continue to come and go without any assistance from man.

Anyone who cannot accept this basic principle should then accept that the dinosaurs must have been very industrious creatures during their time on earth.