In the early 1990s, it would have been hard to imagine the rates of glacial ice loss we are seeing now.
There were few ways to accurately measure the Greenland Ice Sheet’s mass. Snow fell, glaciers calved. But observations seemed to show that the great, cold ice pile over Greenland was in balance. Snow gathered at the top, glaciers calved at the edges, but human heating of the atmosphere had yet to show plainly visible effects.
At that time, climate scientists believed that changes to the ice, as a result of human caused heating, would be slow and gradual, and would probably not begin to appear in force until later in the 21st Century.
(Extensive surface melt ponding, dark snow near the rapidly melt Jakobshavn Glacier on the West Coast of Greenland in early August of 2014. Image source: LANCE MODIS.)
Ice Sheet Response Starts Too Soon
By the late 1990s, various satellites had been lofted to measure the gravity, mass and volume of structures on the Earth’s surface. These sensors, when aimed at the great ice sheets, found that Greenland, during a period of 1997 to 2003 was losing mass at a rate of about 83 cubic kilometers each year.
This rate of ice loss was somewhat small when compared to the vastness of the ice sheet. But the appearance of loss was early and, therefore, some cause for concern. More monitoring of the ice sheet took place as scientists continued their investigation, for it appeared that the ice sheet was more responsive to human warming than initially believed.
A Doubling After Just Six Years
By 2009 another set of measures was in and it found that the six year period from 2003 to 2009 showed a near doubling of ice mass loss from the Greenland Ice Sheet. Rates of loss had jumped from 83 cubic kilometers each year to around 153 cubic kilometers. The doubling caused consternation and speculation among climate scientists. Greenhouse gas heat forcing was rapidly on the rise and the world’s oceans were warming faster than expected as human emissions continued along a worst case scenario path. It appeared that the ocean was delivering heat to the ice sheet bases even as atmospheric warming was melting larger areas upon the ice sheet surface.
These changes to the massive ice sheets were occurring far more rapidly than previously considered.
(Hundreds foot high edge of the Greenland Ice Sheet in Kangerlussuaq as seen at the end of a long valley and across a cold estuary. Image source: EISCAT Scientific Association.)
The potential for a 3, 6, or even 9 foot or more sea level rise by the end of the 21st Century was raised. Perhaps even more ominous, global climate models were showing that rapid ice melt in Greenland and West Antarctica, should it occur, would play havoc with world weather systems. It was this jump in ice loss, in part, that spurred climate scientist and then head of NASA GISS, Dr. James Hansen to write his book The Storms of My Grandchildren as a warning that rapid mitigation in human greenhouse gas emissions along with a stabilization of atmospheric CO2 at 350 ppm would probably be needed to prevent severe consequences from human-caused warming.
But humans kept emitting at a break-neck pace, spending far more money to build coal, gas and oil based technology, than to reduce energy consumption through efficiencies or behavioral change or to invest in alternatives like wind and solar.
Melt Rates Surge Yet Again
And so, by January of 2014, heat forcing had continued to accumulate at a very rapid pace. CO2e heat forcing had spiked to 481 ppm, enough to melt the entire Greenland Ice Sheet and much of Antarctica as well, if maintained or increased over a long period.
And the Greenland Ice sheet was, indeed, melting at an ever faster clip. For the most recent assessment found that the loss rate from Greenland had again more than doubled — hitting a 375 cubic kilometer per year average during the period of January 2011 through January of 2014.
(Greenland Ice Sheet elevation change in meters as found in a recent report by the Alfred Wegner Institute. Note that all Greenland edge zones are now experience elevation losses. Due to higher elevations at the center of the ice sheet, elevation loss at the edge has an effect that speeds ice sheet motion toward the sea. The effect is similar to pushing down the edge of a plastic swimming pool, but on a much larger scale and with somewhat slower moving ice.)
It was an extraordinary rate of melt now 4.7 times faster than in the period from 1997 to 2003 and 2.5 times faster than during 2003 to 2009. But, likely, it is but one more milestone on the path to even faster melt.
The same study that found the Greenland melt acceleration also saw a tripling of the melt rate of West Antarctic since 2003 to 2009. Together, the ice sheets were found to contribute a combined mass loss of 503 cubic kilometers per year between Greenland and West Antarctic. This vast, and still apparently rising, loss now meant that the two great ice sheets were contributing at least one millimeter per year to sea level rise.
Likely Grim Future For Sea Level Rise
It is likely that mass rate losses will continue to increase until some kind of break or negative feedback comes into play. Similar rates of melt increase would mean an annual 5-8 millimeter sea level rise by 2035 due to Greenland and Antarctic melt on top of a 2-3 millimeter sea level rise from thermal expansion of the oceans and from other melt sources. But even taking into account the cooling effect at the ocean surface from ice melt and fresh water floods, one could easily envision the feared 1-3 foot sea level rise by sometime near mid century and the even more concerning 3-9 foot sea level rise amidst a very intense battle between hot and cold weather systems through to century’s end.
As of 2014, it appears the conditions leading up to the warned of “Storms of My Grandchildren” are well in play and rapidly building.
Hat Tip to TodaysGuestIs