Greenland Ice Sheet 150 Billion Tonnes Above Average

In 2018, Greenland’s ice sheet has gained almost 150 billion tonnes of snow and ice above the average for 1981-2010.

It’s time for the Greenland ice sheet’s annual health report, brought to you by scientists from the Danish Meteorological Institute and Polar Portal.

The end of August traditionally marks the end of the melt season for the Greenland ice sheet as it shifts from mostly melting to mostly gaining snow.

As usual, this is the time when the scientists at DMI and our partners in the Polar Portal assess the state of the ice sheet after a year of snowfall and ice melt. Using daily output from a weather forecasting model combined with a model that calculates melt of snow and ice, we calculate the “surface mass budget” (SMB) of the ice sheet.

This budget takes into account the balance between snow that is added to the ice sheet and melting snow and glacier ice that runs off into the ocean. The ice sheet also loses ice by the breaking off, or “calving”, of icebergs from its edge, but that is not included in this type of budget. As a result, the SMB will always be positive – that is, the ice sheet gains more snow than the ice it loses.

For this year, we calculated a total SMB of 517bn tonnes, which is almost 150bn tonnes above the average for 1981-2010, ranking just behind the 2016-17 season as sixth highest on record.

By contrast, the lowest SMB in the record was 2011-2012 with just 38bn tonnes, which shows how variable SMB can be from one year to another.

Maps show the difference between the annual SMB in 2017 (left) and 2018 (right) compared with the 1981-2010 period (in mm of ice melt). Blue shows more ice gain than average and red shows more ice loss than average. (Credit: DMI Polar Portal)

We must wait for data from the GRACE-Follow On (GRACE-FO) satellite mission before we know how the total mass budget has fared this year – which includes calving and melting at the base of the ice sheet. However, it is likely that the relatively high end of season SMB will mean a zero or close-to-zero total mass budget this year, as last year.

The period 2003-2011 has seen ice sheet losses on Greenland averaging 234bn tonnes each year. The neutral mass change in the last two years does not – and cannot – begin to compensate for these losses. The comparison here does show that in any given year, the mass budget of the ice sheet is highly dependent on regional climate variability and specific weather patterns.