Monday, August 17, 2015

melting glaciers

Glaciers are one of the more important topics in climate change.  Snow and ice occur where there are low temperatures and lots of precipitation.  As the atmosphere warms it contains more moisture, and while global temperatures are climbing, whether or not a glacier grows or melts is a complex process involving places where temperatures remain cold and moisture increases precipitation.

Thus while in some places the glaciers are melting, in other places then can be growing, even while the global temperatures are increasing.  Obviously after a certain point, glaciers are likely to completely melt, as happened in the PETM, but we have some ways to go for that to happen at this time.

Global warming deniers like to use glaciation as evidence against warming.  But this is called "cherry picking".  What is happening globally?

That doesn't look good for glaciers.  What is the proportion of growing to melting glaciers?

Figure 2:  Percentage of shrinking and growing glaciers in 2008–2009, from the 2011 WGMS report

So people can point to this or that glacier that is growing, e.g., the Tulutson Glacier in Mt. St. Helens, but globally, far more are shrinking than growing.

Of all the land ice on this planet there are two places that are more important than all the rest because their melting will mean dramatic increases in sea levels endangering coast lines everywhere, the Antarctica and Greenland.  The Antarctic is mixed, part of it is growing where temperatures remain quite cold and the increasing atmospheric moisture is causing increasing precipitation (i.e., snow).  Thus

There is variation between regions within Antarctica (Figure 2, top panel), with the West Antarctic Ice Sheet and the Antarctic Peninsula Ice Sheet losing ice mass, and with an increasing rate. The East Antarctic Ice Sheet is growing slightly over this period but not enough to offset the other losses.  There are of course uncertainties in the estimation methods but independent data from multiple measurement techniques (explained here) all show the same thing, Antarctica is losing land ice as a whole, and these losses are accelerating quickly.

So the situation's complex in the Antarctica.  But the matter's different on Greenland

With an area of 1.71 million km2 and volume of 2.85 million km3, the Greenland ice sheet is the second largest glacial ice mass on Earth. Only the Antarctic ice sheet is larger. The freshwater stored in the Greenland ice sheet has a sea level equivalent of +7.4 m.

In other words, if it were all to melt, the sea would rise about 25 feet.  And how is the ice on Greenland doing?

Figure - Monthly mass anomalies for the Greenland ice sheet

That doesn't look good.