A new study, carried out by scientists at the University of Leeds, demonstrates the extent to which current estimations of Greenland ice loss and its impact on rising sea levels are probably wrong.
Up until now, it has been commonly held that the effect of lakes that form on the ice sheet from melted snow and ice – called supraglacial lakes – was relatively small, but the new study, which simulated their distribution on the surface, has showed there’s a high probability that over the next 50 or so years these “lakes” will move farther inland, which may alter the ice sheet flow in a disastrous way.
According to the lead author Dr. Amber Leeson, a researcher at the School of Earth and Environment: “Supraglacial lakes can increase the speed at which the ice sheet melts and flows, and our research shows that by 2060 the area of Greenland covered by them will double.”
Because of their darker colour, supraglacial lakes absorb more heat from the Sun, which warms up the ice and makes it melt more rapidly. When lake size crosses a certain threshold, it drains through little cracks on the surface, letting the water reach the ice sheet base. Once there, it acts as a lubricant that helps the melting ice to slide into the ocean at an accelerated pace.
“When you pour pancake batter into a pan, if it rushes quickly to the edges of the pan, you end up with a thin pancake. It’s similar to what happens with ice sheets: the faster it flows, the thinner it will be.
“When the ice sheet is thinner, it is at a slightly lower elevation and at the mercy of warmer air temperatures than it would have been if it were thicker, increasing the size of the melt zone around the edge of the ice sheet.”
For now, supraglacial lakes are still restricted to low elevations around the coastline of Greenland, forming in a band that is approximately 100 km wide. Current climate prevailing in the areas further inland are simply too cold for the lakes to form.
However, new data suggests that rising Arctic temperatures will cause the lakes to spread up to 100 km further inland by 2060, effectively doubling the area of Greenland they cover today.
Dr. Leeson added: “The location of these new lakes is important; the will be far enough inland so that water leaking from them will not drain into the oceans as effectively as it does from today’s lakes that are near to the coastline and connected to a network of drainage channels.” This could lead the water from lakes further inland to lubricate the ice more effectively, causing it to speed up.
Loss of ice in Greenland has been expected to contribute about 22 cm to global sea level by 2100, but these estimations did not take into account the changes in supraglacial lake distribution, which the new study highlights.
The Director of Centre for Polar Observation and Modelling, Professor Andrew Shepherd, a co-author of the study, said: “Because ice losses from Greenland are a key signal of global climate change, it’s important that we consider all factors that could affect the rate at which it will lose ice as climate warms.
“Our findings will help to improve the next generation of ice sheet models, so that we can have greater confidence in projections of future sea-level rise. In the meantime, we will continue to monitor changes in the ice sheet losses using satellite measurements.”
Original research article: A. A. Leeson, A. Shepherd, K. Briggs, I. Howat, X. Fettweis, M. Morlighem & E. Rignot, Superglacial lakes on the Greenland ice sheet advance inland under warming climate, 15 December 2014, Nature Climate Change. DOI: 10.1038/nclimate2463