Friday, January 23, 2015

Greenland On The Mind

The National Snow and Ice Data Center (NSIDC) released their 2014 Greenland melt season review on January 22. The first line pretty much summarizes it all:
Melt extent in Greenland was well above average in 2014, tying for the 7th highest extent in the 35-year satellite record.
The figure below showss the surface melt day anomaly for the last four years, the number of melt days compared to the average number of melt days. You can see the pattern hasn't been good. The number of melt days is increasing for the low-altitudes regions.

Source: NSIDC
The NSIDC report stated,

Comparing the seasonal progression of the four most recent years, the recent tendency for greater-than-average melt extent is apparent, as are the rapid variations in melt extent mid-year.
We'll say 2012 was an abnormality and discount that one. Let's hope we don't see any more years like that one. That still leaves a clear pattern of an increased number of melt days these last few years compared to the long-term average number of melt days.

In case you are plan on objecting on the basis the interior is experiencing a normal melt routine, consider these facts:
  • As the ice melts the higher altitudes get lower every year, increasing the number of melt days;
  • As the coastal ice melts, the interior ice will push out and spread, again bringing the higher altitude ice down;
  • As the melt season increases it results in dark pools of water sitting on the surface for longer periods of time where they absorb more sunlight than the reflective ice, increasing the amount of melting.

In the paper, The pattern of anthropogenic signal emergence in Greenland Ice Sheet surface mass balance, published in Geophysical Research Letters last August, researchers concluded human-driven climate change is increasingly responsible for current trends in Greenland Ice Sheet melt and accumulation. They also concluded human activity will dominate further melt and accumulation  pattern throughout the 21st century. 

In case you still think the Greenland Ice Sheet is recovering, take a look at this graph:

Source: Polar Portal
This graph shows the mass of the Greenland Ice Sheet as measured using the GRACE satellite. The mass increases during the winter accumulation season and then drops during the summer melt season. The downward trend is pretty obvious. More ice is melting away in the summers than is being deposited by snow in the winters. In fact, we can see the mass of the ice sheet has decreased by more than 2800 billion tons since just 2004.

By the way, the NSIDC report also said the top eight melt extent years have all occurred since 2002.

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