How land ice influences climate

The fourth Delft Climate Institute symposium (October 17 2013) focused on ice sheets. Not only do these erode as a consequence of climate change, they influence climate as well. That exchange has now been quantified.

Last July, a record temperature of 26 degrees Celsius was measured in Greenland. And in 2012 the land ice had melted so much that the underlying bedrock emerged at the surface. Climate scientists take such incidents pretty seriously, because they know that the Greenland ice can raise ocean levels by 7 meters, and Antarctica ice by 57 meters. That said, they also know that such mega-events will not happen overnight.

To get a grip on the dynamics of the icesheets, especially those of Greenland and Antarctica, scientist make clever use of data from various satellites to arrive at what they call the Ice Sheet Mass Balance. Professor Michiel van den Broeke (Utrecht University) explained that the measured ice sheet loss is a combination of increased ice-flow, less snow fall and more run-off of melt water. Researchers have figured out in detail the various contributions.

Scientists need data from remote sensing satellites to test their models. The GRACE satellite pair maps ice mass loss, which is especially high in the South East and North West of Greenland. Other satellites like ICESat (retired) and Cryosat (still active) map the surface height of the land ice, being a function of the melt and them fresh accumulation of snow.

Making use of the latest remote sensing and ice sheet models, Professor Pavel Ditmar (geoscience and remote sensing, faculty of CEGS) calculated that the current net mass loss could reliably set to 142 gigatonnes per year for Greenland and half of that for Antarctica.

Climate modeler Dr. Miren Vizcaino (Utrecht and Delft University) told the audience about a recent breakthrough by means of which she had included the influence of ice sheets on climate models. And not vice-versa as is the usual approach. Ice sheets influence the local climate through their whiteness (called albedo) which reflects most of the sun’s radiation. Ice sheets also influence fresh water fluxes and sea ice formation. Plus, they have a large influence on the land cover since when ice melts, all radiation gets absorbed.

Vizcaino worked hard to include the surface ice mass balance of Greenland into the regional climate model. In other words she worked to quantify the effect the land ice has on the regional climate. Comparison with actual weather stations showed that the model underestimated the mass loss at the rainy South East side of Greenland, but was mostly accurate. 

The challenge now is to extend beyond Greenland and to model the influence of ice sheets on a global model such as the Community Earth System Model or CESM. “Our results confirm that ice sheets should not be considered as a passive component of the climate system in projections of anthropogenic climate change”, says Vizcaino.

Ice sheets seem to buffer the effects of climate change. But with the ice sheets themselves slowly disappearing, so does the climate mitigation we are accustomed to.

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