Polar ice sheets on Antarctica and Greenland are melting, raising sea levels.
This is a fact.
But what is up for debate is how quickly it’s happening.
Today, Nov. 29, a group of researchers have published a new study combining 20 years of research, giving the most accurate measurements of ice sheet loss we’ve ever had.
Researchers are worried about the polar ice melting because the meltwater goes into the oceans, raising sea level. Recent studies have shown that sea level is rising 60 per cent faster than expected — about 3.2 millimeters a year. Rising seas threaten the lives of people who live near the ocean and low-lying lands, like some islands that scientists think could completely vanish.
Why is this happening? Green house gases from burning fuels are causing runaway warming on a global scale — and warmer temperatures melt the ice.
Greenland has been covered by ice for about three million years, and Antarctica has been covered for about eight million years. Latest estimates indicate that there are 680,000 cubic miles of ice on Greenland, which would raise the oceans by more than 20 feet if it were to melt completely.
Since 1998 there have been at least 79 estimates of the melting of ice sheets on Antarctica and Greenland, all of which have some flaws. These flaws include: only looking at certain regions, not studying the ice sheets over the long term, or only using one technique to measure ice loss, since each technique has their own flaws.
Andrew Shepherd from the University of Leeds in the UK and his colleagues complied data from 1992 to 2011 using satellites to measure changes in elevation, velocity of ice sheets, changes in gravity, and precipitation. Combing these methods carefully and overlapping time and geography from the different studies adds certainty to the measurements.
Their results show that since 1992 Antarctica has lost about 1,320 gigatons of ice and Greenland has lost 2,940 gigatons. This melt has contributed to 11 millimeters of sea level increase.
Previous estimates from 1958 to 2010 have been all over the map. Estimates of yearly mass change for Antarctica ranged between a loss of 246 gigatons and a gain of 27 gigatons. In Greenland annual estimates ranged from a loss of 308 gigatons to a gain of 10 gigatons.
Photo: Ian Joughin
This is only part of the total sea level rise of almost six centimeters since 1995, and are now rising faster than expected. Other sources of rising levels include the melting of other glaciers (like the Himalayas) and the expanding of the ocean as it warms with the rest of the Earth.
They noted that both of the polar ice sheets seem to be melting more rapidly than they thought from previous observations. Greenland is losing five times more mass today than it was in the early 1990’s and Antarctica is losing 50 per cent more ice.
Photo: Ian Joughin
When asked what this meant for future melt, the researchers warned that any prediction they made now would be inaccurate because we can’t be sure how much the Earth will warm. There are many variables adding to the ice melt and rising temperatures.
Over the summer there was a massive sweep of warm air and melting of ice in Greenland. As ice melts, the land absorbs more energy from the sun (since ice reflects light, and darker areas absorb it). This energy raises temperatures, and makes the ice melt even faster.
Even the Intergovernmental Panel on Climate Change has concluded they could no longer place limits as to how much ice melt will contribute to sea levels rising because the melting keeps increasing — the only thing the researchers know for sure is that ice sheets are definitely melting and sea levels are certainly rising.
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