Maybe it is just a coincidence, but last week saw the release (or pre-release) of two more studies confirming that the rate of melting on Greenland and Antarctica has accelerated in just the last decade. Greenland is showing increased melting and glacial runoff as temperatures are rising in the North Atlantic, and Antarctica is showing significant loss of ice on the Antarctic Peninsula and in the western part of the Southern Continent.
First, Greenland. It has been a focal point of the debate(?!) on climate change in recent years as the Greenland Ice Sheet (GrIS) is melting at a significant pace. This melting was thought to be more of an issue for coastal glaciers rather than the interior ice cap that covers the higher altitudes on the island as this area still shows at least a net gain in snow and ice (Science Magazine), but now scientists are seeing that as the ice sheet is melting, the water pools up on the surface and then seeps downward into the glaciers, turning into "moulins" or vertical rivers that create holes within the glacial structure, but then also flow under the ice acting as a lubricant to the glaciers as they "speed" toward the sea. It has been thought that snow and ice accumulation in the interior higher-altitude ice cap would balance the loss of coastal ice, but now it seems that the balance is just not there. Science Magazine reports that the only gain to the GrIS "is found in the vast interior areas above 1500 meters, in contrast to previous reports of high-elevation balance. Below 1500 meters, the elevation-change rate is -2.0 ± 0.9 cm/year, in qualitative agreement with reported thinning in the ice-sheet margins." (Science Magazine)
Don't get too excited about the gain. That information is now over two years old. We are still waiting to see newer reports to confirm if this gain is continuing.
Researchers led by Edward Hanna from the University of Sheffield just released news that the GrIS is showing increased melt in the last 15 years. Before that time, going back to records from the 1960's, there was no real correlation between the rate of melt and the temperatures in the Northern Atlantic. However, as the newer research shows, suddenly things starting changing around 1990. Temperatures started going up, and then the rate of melt started increasing in similar ratios.
The significant increases in observed Greenland margin summer temperatures and modelled runoff, the new 2003 and 2005 observed temperature and snowmelt records, and highly significant correlation of recent Greenland with Northern Hemisphere temperatures since the early 1990s, collectively suggest that an expected response of the GrIS to global warming may well be emerging. -- Hanna et alHonestly, these findings are not new or surprising. A report in Science Magazine from 2006 shows almost exactly the same thing. The latest study is simply looking at more complete data sets, and thus confirming what scientists have been noticing since the 1990s.
Obviously, melting is something that all glaciers and ice sheets do. The world's largest and most important rivers are almost always fed by far-off mountain glaciers that collect ice and snow all winter, discharging it throughout the spring and summer as rivers. Greenland is really no different, except that being an island the glacial runoff enters the ocean system (which poses other issues that I will discuss later).
The latest studies are estimating that although Greenland's Ice Sheet is accumulating precipitation, the rate of melt is outpacing the accumulation.
Last year, satellite data collected by NASA scientists revealed Greenland is losing 100 billion tons of ice each year, more than it is gaining from snowfall in the interior. Steffen and others have also detected a new, faster movement of the ice sheet, causing the glaciers to dump more ice into the ocean, where it melts and contributes to sea-level rise.-- CNNSo, as that last quote just mentioned, yes, sea level rise can and will be a problem for many, many millions of people. Couple that with what would be a rather large influx of fresh water into sea water at the top of the North Atlantic portion of the Ocean Conveyer Belt (Thermohaline Circulation) and that condition can further cause abrupt and devastating changes to not only the North Atlantic, but the entire globe.
Although various models give differing results, any changes in the thermohaline circulation will have profound consequences for marine biology and fisheries because of inevitable changes in habitat and nutrient supply. Perturbations caused by projected climate change, such as a marked increase in freshwater inputs in polar regions, may cause reorganization of the global ocean thermohaline circulation, leading to abrupt climate change (e.g., Manabe and Stouffer, 1993; Wright and Stocker, 1993; Stocker and Schmittner, 1997). Palaeoclimatic effects of past large freshwater inputs are widely discussed for the Atlantic (e.g., Broecker et al., 1990; Rasmussen et al., 1996; Bianchi and McCave, 1999) and for extra melt from the Antarctic ice sheet (Mikolajewicz, 1998). These studies show that with past climate changes, shifts from one circulation mode to another have caused large, and sometimes abrupt, regional climate changes. Although there is low confidence that such events will occur, the associated impacts would be substantial. -- UN Environmental ProgrammeAs you can see from the references in the above UNEP quote, studies on the effects of the polar regions melting have been going on for quite some time now. These studies were always meant to be more academic (at least that is what we have all been hoping) rather than a bleak picture of things to come, but with the latest data coming on line and examined in the context of the last century, it is becoming harder for climate change sceptics and their arguments to, ahem, hold any water. Even if the polar ice caps hold out for a few more centuries, no one can really say what the threshold is for freshwater tipping the balance of the Ocean Conveyer Belt, which is responsible for not only distributing heat around the globe, but also weather patterns.
So, now let's talk about Antarctica, which holds a special place in my heart. Nature Geoscience posted an online advance publication of the latest examination of data from Antarctica last week. I have not been able to read to entire article (being as yet unpublished), but here is a partial abstract that I read to a girl scout troop last night around a camp fire in place of a ghost story.
I added the [or]'s, and Gt means Giga-tonne or Giga-ton.
We compare the mass fluxes from large drainage basin units with interior snow accumulation calculated from a regional atmospheric climate model for 1980 to 2004. In East Antarctica, small glacier losses in Wilkes Land and glacier gains at the mouths of the Filchner and Ross ice shelves combine to a near-zero loss of 4 plus [or] minus 61 Gt yr-1. In West Antarctica, widespread losses along the Bellingshausen and Amundsen seas increased the ice sheet loss by 59% in 10 years to reach 132 plus [or] minus 60 Gt yr-1 in 2006. In the Peninsula, losses increased by 140% to reach 60 plus [or] minus 46 Gt yr-1 in 2006. Losses are concentrated along narrow channels occupied by outlet glaciers and are caused by ongoing and past glacier acceleration. Changes in glacier flow therefore have a significant, if not dominant impact on ice sheet mass balance. --Nature Geoscience
Antarctic hot zones
Here's just one more piece of this puzzle that I will leave you with. Most scientists agree that the "gain" of snowfall in the polar regions is actually in itself a result of a warming world. You see, warmer air can hold more water. Remember chemistry class. Heat means the atoms in the molecules are moving more and expanding a bit. The expansion in the air molecules means more room for water molecules to hitch a ride. So if the poles are receiving more snow, that means that warmer air is moving that way. That in and of itself is also a troubling sign for the Arctic and Antarctic. Last year's Nobel-winning IPCC panel report didn't really factor Antarctica increased ice loss because at the time the evidence of net loss was still a bit on the inclusive side. Unfortunately, this new data lends a bit more credibility to the potential one meter sea level rise that the IPCC predicted by 2100, and then some.
Oh, yeah, and if someone tells you that some climatologists are forecasting that 2008 is supposed to cool down from the last three or seven years, they are not reading the full story. Reuters did report that "2008 will be slightly cooler than recent years globally..." Keep reading, and you find "but will still be among the top 10 warmest years since records began in 1850 and should not be seen as a sign global warming was on the wane, British forecasters said." (Reuters)