Current melting at the surface of the Greenland ice sheet is unprecedented for at least the last three-and-a-half centuries. That is what a group of climate researchers from the US, Belgium and Utrecht report today in the journal Nature, based on melt records from three ice cores drilled in central west Greenland. Brice Noël, postdoctoral researcher at the Institute for Marine and Atmospheric Research of Utrecht University (IMAU), played an important role in the research by contributing an advanced polar climate model. “This model translates the local melt history stored in the ice cores to the whole of Greenland.”
350 years of Greenland ice melt reconstructed
Modern Greenland ice sheet melt unprecedented since age of industrialisation
Surface melt on the Greenland ice sheet – the second largest body of land ice on earth - began to increase after the onset of the industrial-era in the mid-1800s and ramped up dramatically during the 20th and 21st centuries. The ice sheet now contributes significantly to global sea level rise. In this study, scientists from the US and Belgium worked together with Brice Noël and Michiel van den Broeke from IMAU at Utrecht University, who contributed an advanced polar climate model that extrapolated the melt from the ice core locations to the entire Greenland ice sheet.
Three ice cores
The basic data for this study were derived from three ice cores drilled in the ice of central west Greenland by the US team. In this part of the ice sheet all surface melt refreezes in the snow, preserving centuries of local melt history. Noël explains how it works: “Every year in summer, the top layer of snow melts and this meltwater percolates downward in the snow, where it refreezes. In the cores, you see this as a layer of ice with a higher density surrounded by snow. The thicker the ice layer, the more melt occurred during that specific year.”
350 years of ice melt
In those ice cores, a Greenland melt history from the last 350 years is stored. Noël: “Prior to the satellite era in 1978, estimates of Greenland melt remained highly uncertain. As a result, no conclusions could be drawn for the centuries when modern methods weren’t available yet.” The three ice cores, however, revealed valuable information on the local amount of melt since the 17th century that could be used to estimate surface melting over the whole ice sheet back in time.
To translate the melt history stored in the three ice cores to the whole of Greenland, an advanced polar climate model proved essential. Noël says: ”Our climate model was used to extrapolate that local melt information from the ice core sites to the full Greenland ice sheet. Because the model reaches a kilometer resolution, we could even determine how small glaciers on the jagged coastline of Greenland have responded.”
Noël: “It turns out that the amount of melt has been increasing since the middle of the 19th century, with a dramatic intensification in the last two decades.” The reason is that Greenland ice sheet melt is highly non-linear; this means that when it gets warmer, it takes an ever-smaller temperature increase to cause the same increase in melt. Noël concludes: “This study proves that warming today means a larger increase in ice melt than it did in the past.”
Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming
Luke D. Trusel, Sarah B. Das, Matthew B. Osman, Matthew J. Evans, Ben E. Smith, Xavier Fettweis, Joseph R. McConnell, Brice P. Y. Noël*, Michiel R. van den Broeke*
Nature, 6 December 2018, DOI 10.1038/s41586-018-0752-4
* affiliated with Utrecht University
This research was made possible with support from the Netherlands Earth System Science Centre (NESSC) and the Netherlands Polar Programme of the Netherlands Organisation for Scientific Research (NWO).