The real breakthrough has come with the increasing number of observations that have allowed the scientists to independently check how well the computer models are able to simulate the Greenland ice sheet. Project co-Principal Investigator, Professor Jason Box at GEUS is clear that not only the weather stations that GEUS-PROMICE have been installing and maintaining, but also the years of fieldwork, using a range of techniques from radar to shallow cores and snow pits, have been vital for being able to develop and assess the new model. “The Greenland ice sheet is really going through a period of change. We saw that last year with the extremely early start to melting. This can really make it challenging to do fieldwork just when we need long-term records more than ever. With these new model parameters we can now see how important these early melt events can be”.

DTU PhD student Baptiste Vandecrux concurs “On the ACT-16 Arctic circle traverse across the Greenland ice sheet last year, we experienced some pretty challenging conditions due to the early melt event, but this makes our work on the model and the observations even more interesting and important”.

The early melt in 2016 was reported by polar portal scientists on the 12th April 2016. Based on this work, it was argued already then that it would not have much overall impact on how much ice Greenland would lose. As co-author Dr. Robert Fausto from GEUS puts it, “When we compare the model results with sensors in the snow or with observations from snow pit we can see that much of this meltwater in the early part of the season stays within the snowpack either as liquid water or as ice lenses, which means we can really estimate quite well how much water is retained in the ice sheet”.

It’s not all good news however, “the bad news is that observations and models also show that widespread melting and the formation of thick ice layers in the snow, effectively creating an ice lid, preventing further drainage down deep into the snowpack, so later in the year we get much more runoff. It’s important to understand these processes as we need to know when the melt happens and where the water goes. This also helps us to quantify how much the surface melt of Greenland is contributing to sea level rise at the present day, and how quickly this will likely increase in the future”.

The Retain project also has a benefit for the Polar Portal as we can use the upgraded model to extend and improve the daily estimated surface mass balance. We expect to introduce this new data over the next few weeks.

Full reference :

Langen, P.L., Fausto, R.S., Vandecrux, B., Mottram, R.H., Box, J.E., 2017. Liquid Water Flow and Retention on the Greenland Ice Sheet in the Regional Climate Model HIRHAM5: Local and Large-Scale Impacts. Front. Earth Sci. 4. doi:10.3389/feart.2016.00110 http://journal.frontiersin.org/article/10.3389/feart.2016.00110/full

This is a contribution to the special issue in Frontiers in Science on Melt Water Retention Processes in Snow and Firn on Ice Sheets and Glaciers: Observations and Modeling, curated by Retain project members.

Learn more about the Danish Council for Independent Research funded Retain project here: http://retain.geus.dk/ (Grant no. 4002-00234).

Polar Portal is collaboration between DMI, GEUS, DTU-Space and DTU-Byg with funding from the Danish Energy Agency (Energistyrelsen)