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Global WarmingScience

Greenland Ice Sheet a Complex Mystery

With warming temperatures worldwide much speculation has been focused on how the Antarctic and Greenland ice-sheets will react. Hotter temperatures, in theory, should be bad for ice, but according to new research published in a letter in the 27 January edition of the journal Nature, hotter summers may not be as catastrophic for the Greenland ice-sheet as had previously been supposed.

The letter referred to a study conducted by Professor Andrew Shepherd from the University of Leeds School of Earth and Environment, and noted that as the melting increases in warmer years, the drainage system of the ice-sheet adapts and accommodates more melt-water, without speeding up the flow of ice towards the oceans.

“It had been thought that more surface melting would cause the ice sheet to speed up and retreat faster, but our study suggests that the opposite could in fact be true,” said Shepherd.

“If that’s the case, increases in surface melting expected over the 21st century may have no affect on the rate of ice loss through flow. However, this doesn’t mean that the ice sheet is safe from climate change, because the impact of ocean-driven melting remains uncertain.”

The Greenland ice-sheet covers approximately 80% of the island and holds enough water to raise the world’s sea levels by 7 metres if it were to completely melt. Additionally, the influx of so much freshwater into the ocean would have catastrophic effects on the ocean currents and, subsequently, the climate conditions of much of the northern hemisphere.

Rising temperatures in the Arctic have reduced the size of the Greenland ice-sheet, prompting fears that it might be close to a point where there is nothing that can be done to save it, a tipping point.

Some of the ice loss has been attributed to the speed up of glaciers due to increased surface melting. As summer turns around, the surface of the ice-sheet melts, causing water to run down a series of channels which lead to the base of the glacier where the water pools, sometimes creating huge underground lakes, other times simply acting as a lubricant for the glacier to slide across the bedrock.

However the new study by Shepherd and colleagues suggests that the opposite of this could in fact be true.

Shepherd and his team used satellite observations of six landlocked glaciers in south-west Greenland, acquired by the European Space Agency, to study how ice flow develops in years of markedly different melting.

Despite the fact that the initial speed up of ice melting was similar in all years, slowdown occurred soonest in years which were warmer than others, suggesting that these years of abundance triggers an early switch in the plumbing at the base of the ice, causing a pressure drop that slows down the ice speeds, behaviour that is similar to mountain glaciers, which sees summertime speed up of ice reduce once the melt-water from the glaciers can drain efficiently.

“This work also underlines the usefulness of modern gridded climate datasets and melt-model simulations for exploring seasonal and year-to-year variations in Greenland ice sheet dynamics and their relationship with the global climate system,” added study co-author Dr Edward Hanna from the University of Sheffield.

Source: The University of Leeds
Image Source: basheertome




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