By Paul Homewood
http://www.dmi.dk/en/groenland/maalinger/greenland-ice-sheet-surface-mass-budget/#
As I pointed out the other day, the surface mass balance (SMB) in Greenland has increased way above the long term average for the second year running.
The question was raised as to the significance of this, given that the SMB does not include losses from calving. The DMI page on the SMB quotes:
The calving loss is greater than the gain from surface mass balance, and Greenland is losing mass at about 200 Gt/yr.
However, care needs to be taken with this, as the same statement has appeared every year recently, for instance in 2013 (see here). It is just a stock statement.
The simple answer is that the SMB is an extremely important part of the equation, otherwise DMI would not even be bothering to show it at all. Great effort is put into calculating SMB changes every single day of the year. The DMI certainly regard it as an extremely important measure.
It is also true that one of the most important determinants of glacier/ice sheet formation is snow downput, which in turn feeds into the SMB.
It also needs to be stated that, as far as I am aware, neither the DMI nor anybody else publishes regular estimates of calving loss. So, like it or not, we are left with SMB.
To put SMB into perspective, the DMI’s Ruth Mottram produced this table and chart in her paper, Surface mass balance of the Greenland ice sheet in the regional climate model HIRHAM5: Present state and future prospects, in 2017:
In other words, the SMB fell from 375 Gt pa in the 1980s, to 277 Gt between 2000 and 2014.
IPCC AR5 also gave us some figures for total ice loss, including calving, which mention a loss of 215 Gt pa from 2002-11:
https://ipcc.ch/report/ar5/wg1/
This would imply a loss from calving of roughly 500 Gt a year. Therefore an increase to over 500 Gt in the SMB for the last two years is highly significant, as it means that there is no ice loss at all.
Of course, this is only two years worth of data; mere weather. Arguably though, so was the last decade. We certainly need to be looking at decades of data, covering the major ocean cycles.
And, of course, we should not be surprised that Greenland’s glaciers are receding, given that scientists say they were at their maximum extent since the early Holocene during the Little Ice Age.
No doubt, Greenland’s glaciers will continue to recede in the long term, just as they have in the past century.
The real question is whether ice loss will accelerate. And the answer to that lies in the SMB.
Will we see the great Greenland meltdown, that we hear so much about?
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August 26, 2018 at 11:10AM
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