At a dinner I attended last night, glaciologist Jason Box explained why he believes Greenland’s disintegration is likely to keep outpacing Antarctica’s for the foreseeable future. He has a detailed explanation at his blog, Meltfactor, reposted below. See also Chris Mooney’s interview of Box here and “Greenland Ice Melt Up Nearly Five-Fold Since Mid-1990s“ – JR.
Changes in global sea level due to ice sheet melting since 1992. Credit: ESA/NASA/Planetary Visions via NBC.
Icy contenders weigh in
by Jason Box, Ph.D.
Dahl-Jensen et al. (2013)[i] suggest that the Greenland ice sheet was more stable than previously thought[ii], enduring ~6k years of temperatures 5-8 C above the most recent 1000 years during the Eemian interglacial 118-126k years before present, its loss at the time contributing an estimated 2 m (6.6 ft) of global sea level compared to a total of 4-8 m (13-26 ft)[iii], implying Antarctica was and will become the dominant source of sea level change. Consequently, environmental journalist Andrew Revkin writes: “The dramatic surface melting [in Greenland], while important to track and understand has little policy significance.”
Given the non-trivial complexity of the issue and that Greenland has been contributing more than 2:1 that of Antarctica to global sea level in the recent 19 years (1992-2010)[iv], let’s not consider Greenland of neglible policy relevance until that ratio is 1:1 if not reversed, say, 0.5:1. Greenland, currently the leading contender with surface melting dominating its mass budget[v], the positive feedback with surface melting and ice reflectivity doubling Greenland’s surface melt since year 2000[vi]. Professor Richard Alley weighs in again: “We have high confidence that warming will shrink Greenland, by enough to matter a lot to coastal planners.”
That’s not to say that Antarctica couldn’t take over from Greenland the position of number 1 global sea level contributor in the foreseeable future. Nor should one be surprised if it did, given that Antarctica contains a factor of 10 more ice than Greenland[vii],[viii]. And it is probable that the planetary energy imbalance[ix] caused by elevated greenhouse gasses, expressed primarily through massive oceanic heat uptake[x], is delivering enough erosive power to destabilize the 3.3 m of sea level[xi] in the marine-based West Antarctic ice sheet. Yet, for today, consider also that climate change if increasing Antarctic precipitation a few percent can tip its mass balance toward the positive, lessening its sea level contribution[xii] even while its glaciers retreat.
Irrespective of sea level forcing, through its ice mass budget Greenland plays an important role to North Atlantic climate through ocean thermohaline circulation, even being suggested as the Achilles heel of the global climate system[xiii]. I wouldn’t tell our European friends Greenland’s hardly policy-relevant when climate change offers higher amplitude extremes in precipitation if not also temperature, as North Atlantic climate shifts in partial response to changes in neighboring Greenland.
Key differences between the modern Anthropocene and the Eemian interglacial suggest anthropogenic climate change may drive a different cryosphere response than during the Eemian…