Topography affects the speed at which ice moves.
Just as the global temperature rise is likely to be sporadic, so too will the melting of the world’s glaciers. Greenland’s main ocean-draining “outlet” glaciers retreated alarmingly during the past decade, some of them doubling their flow speed as they thinned. The IPCC considered this behaviour so capricious that they left outlet glaciers out of their last models.
An international team led by Faezeh Nick at Svarlbad University in Norway has now shown that this behaviour can be explained by considering the shape of the fjord through which the glacier flows. Glaciers can retreat rapidly through broad valleys, but the retreat will slow through the narrower valleys higher up the glacier.
By mapping four key glaciers, which collectively drain 22% of Greenland’s ice sheet, the team could predict their retreat – and contribution to sea level rise – up to the year 2200.
Should global temperatures reach 4.5 °C above 1990 levels by 2100, these glaciers combined will contribute a mere 49mm to sea levels by 2100, the team predicts.