A Farewell to Ice: A Report from the Arctic by Peter Wadhams
Author:Peter Wadhams [Wadhams, Peter]
Language: eng
Format: epub, pdf
ISBN: 9780241009420
Publisher: Penguin Books Ltd
Published: 2016-08-31T18:30:00+00:00
Figure 8.2: Changes in the mass balance of glaciers in different regions of the globe.
There are some other minor factors involved in the eustatic sea level rise. One is the transfer of fossil aquifer water into the hydrology cycle. As groundwater is pumped out of underground aquifers, where it has been inaccessible to the atmosphere for many millennia, it is used and then runs off into rivers, evaporates into the atmosphere and is eventually added to the water mass of the ocean. This makes a positive contribution to sea level rise, while other man-made effects, such as water being held back in dams, has a net negative effect because the number of dams in the world is constantly increasing.
Another minor feedback is connected to the change in ice altitude on the ice caps. The overall elevation of the Greenland ice sheet itself is beginning slowly to decrease, and the lower it gets, the higher is the surface temperature of the ice cap (because temperatures are lower at higher altitudes), so the more it melts in the summer. This in itself causes the surface elevation to decline faster, leading to more warming, and so on in a feedback loop. This effect is probably small at the moment, but could become more significant in later stages of decline of the ice sheet, speeding its final demise.
The Antarctic ice sheet has been assumed until recently to be in approximately neutral mass balance, because any melt was offset by snowfall, especially on the mountains around the Antarctic coastlines. But now GRACE has been applied to the Antarctic, too, and has observed the Antarctic ice sheet also to be definitely in retreat, though not yet as fast as Greenland.5 The latest estimate is that the Antarctic ice sheet is losing 84 km3 per year, compared to at least 300 km3 for Greenland. It is alarming, though, because there is much more ice in the Antarctic to melt, the equivalent of 60 metres of sea level rise. Also, glaciologists calculate that one part of the Antarctic ice sheet, the West Antarctic ice sheet in the Antarctic Peninsula area, is less stable than previously thought, and after a substantial amount of melt could break away from its base. This on its own would produce a sudden sea level rise of several metres.
In the face of these worrying threats the IPCC has been complacent. Indeed in 2007, in its Fourth Assessment Report (AR4), it was seriously so. Because they had difficulty in estimating the eustatic sea level rise, the IPCC authors gave only the steric rise and extrapolated this to the end of the century to give a mere 30 cm of sea level rise by 2100. They pointed out that this was a partial figure that did not include glacier melt, but most non-scientists and policymakers did not read the small print and some very serious underestimates of sea level rise have been used by national bodies responsible for flood defences, for instance the city authorities of Shanghai.
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