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Wednesday, December 11, 2019

Does Greenland's meltng ice sheet suggest climate change is irreversible?

The Guardian reports that Greenland’s ice sheet is melting much faster than previously thought, threatening hundreds of millions of people with inundation and bringing some of the irreversible impacts of the climate emergency much closer.

They refer to data that suggests ice is being lost from Greenland seven times faster than it was in the 1990s, and the scale and speed of ice loss is much higher than was predicted in the comprehensive studies of global climate science by the Intergovernmental Panel on Climate Change.

As a result it is believed that sea level rises are likely to reach 67cm by 2100, about 7cm more than the IPCC’s main prediction, putting 400 million people at risk of flooding every year, instead of the 360 million predicted by the IPCC, by the end of the century:

Sea level rises also add to the risk of storm surges, when the fiercer storms made more likely by global heating batter coastal regions. These impacts are likely to strike coastal areas all around the world.

“These are not unlikely events or small impacts,” said Andrew Shepherd, professor of earth observation at the University of Leeds, one of the lead authors of the study. “[These impacts] are happening and will be devastating for coastal communities.”

Greenland has lost 3.8tn tonnes of ice since 1992, and the rate of ice loss has risen from 33bn tonnes a year in the 1990s to 254bn tonnes a year in the past decade. Greenland’s ice contributes directly to sea level rises as it melts because it rests on a large land mass, unlike the floating sea ice that makes up much of the rest of the Arctic ice cap.

About half of the ice loss from Greenland was from melting driven by air surface temperatures, which have risen much faster in the Arctic than the global average, and the rest was from the speeding up of the flow of ice into the sea from glaciers, driven by the warming ocean.

Oceans have absorbed most of the excess heat arising from our disruption of the climate to date, and much of the carbon dioxide, but they are reaching the limits of their capacity to do so. Sea level rises are driven not only by melting ice but by the thermal expansion of the seas as they warm.

The paper adds that some experts are concerned that the IPCC's findings do not take into account the potential for “tipping points”, thresholds beyond which climate breakdown accelerates and becomes catastrophic and irreversible:

Louise Sime, a climate scientist at the British Antarctic Survey, said of the new paper: “This finding should be of huge concern for all those who will be affected by sea level rise. If this very high rate of ice loss continues, it is possible that new tipping points may be breached sooner than we previously thought.”

Have we now reached the point when, whatever we do, the devastating impact of climate change is now unstopable?
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