In 1995, Greenland contributed no melt water to global sea level rise. By 2012, melt had increased rapidly to more than 7 mm. By comparison, Antarctica contributed about 4 mm by 2012. Ever since 2003, melt rate growth from Greenland has outpaced that of Antarctica.
In total, Greenland contains enough ice to increase world sea levels by about 6 meters or 20 feet. Quite a lot of water. By comparison, West Antarctica, which is most likely to melt alongside Greenland due to human-caused global warming, contains enough ice to raise sea levels by about 5 meters (16.5 feet). The last time greenhouse gasses were as high as they are today, both these ice stores melted. Along with thermal expansion of water and additional contributions from mountain glaciers and other parts of Antarctica, total sea level rise at around 400 ppm CO2 was about 75 feet.
As the globe warms due to human-caused climate change, we can expect increasing outflows of water from both Greenland and West Antarctica. To prevent such changes, at the very least, will require serious improvements to world energy and climate policy. And so monitoring ice melt in these regions cannot be entirely divorced from the need for such policy if we are to maintain a world with stable coastlines, a world in which states and nations aren’t at risk of being wiped off the face of the Earth by rising waters.
So one wonders why Andrew Revkin recently made this statement in his dotEarth blog:
“The dramatic surface melting [in Greenland], while important to track and understand has little policy significance.”
Revkin’s statement has to do with a recent ice core sample study which found that, during the Eemian, the last inter-glacial period, Greenland melted ‘only’ enough to increase sea levels by 1-2 meters. The study did not conclude, as Revkin did, that Greenland ice melt caused by increases in greenhouse gas emissions would follow the same pattern as it did in the Eemian. Nor did it recommend, as Revkin did, divorcing policy from observations of increasing Greenland ice melt.
Revkin’s argument and assertions aren’t new. In fact, James Hansen in his most recent paper on Greenland and West Antarctic ice melt cautions that melt in Greenland is not likely to follow the same pattern as the Eemian and that inland glaciers aren’t so buttressed from ocean influence as some suppose. Even more disturbing is the fact that some climate change deniers tend to use the Eemian to support some of their own, non-scientific, arguments.
Professor Richard Alley, whom Revkin interviewed in his blog, had his own response to this point by Revkin:
“We have high confidence that warming will shrink Greenland, by enough to matter a lot to coastal planners.”
In other words, Greenland melt has serious policy implications for coastal planners (and many more people, for that matter). A recent report found that Miami may well not be a viable city before the end of this century and, possibly, before it is even half over. Much of south Florida and many low-lying regions of the world are likely to suffer similar fates.
In general, it is not a good idea to suppose that current melt trends will mirror those of the Eemian. Nor that melt will be as gradual as some expect. Nor that we should not base policy decisions on an observable and increasing danger of damaging sea level rise.