Claim: Greenland is actually gaining ice, not losing it as global warming alarmists would have you believe ``The evidence so far suggests that the Greenland ice sheet is actually growing on average" - Richard Lindzen, quoted here

Why this claim is wrong: Cherry-picking, basically is the answer. The cold high altitude interior of Greenland did have a net gain of snow during the '90's, but this was found to be consistent with global warming models, which include higher evaporation of warmer ocean water and deposition as snow at the very high elevations of the top of the Greenland ice cap, which was then still cold enough to have the net snow balance be positive. However, the ERS-1 and ERS-2 satellite data used was not able to say much about the behavior of ice near the coastal areas, where in fact ice has been melting and sliding into the ocean at an accelerating rate. And, since the most often used study which AGW-denialists use to champion this myth was published over a decade ago, newer and better GRACE satellite data using gravity measurements show that the entire continent is net losing ice at a rapidly accelerating rate (this YouTube shows how GRACE works). A recent paper by Wu et al. (2010) using a different calibration of GRACE data, still finds Greenland is losing its icecap. The graph at left shows the change in the total ice mass of Greenland, interior+coasts. The regular up/down oscillations are due to seasonal summer melting vs winter ice accumulation, not observational error. Note that the rate at which the ice is disappearing has doubled during just this last decade - a decade during which the solar heating contribution has actually been dropping as we've gone from a solar maximum in 2001 to an unusually deep solar minimum in 2008/9. Ice loss rate is now seen to have redoubled again from 2009 to 2013. This trend is beyond exponential, and strongly suggests oversimplified old estimates of ice loss in a warming world need to be redone. Ice loss is also happening in Antarctica (and here). A major factor is that the speed of Greenland glaciers is rising rapidly. Meltwater on the surface is observed to follow channels down to the base of the glacier, lubricating its gravity-induced motion towards the ocean. Without detailed images of the base of glaciers, it was difficult to model this with any confidence and so to be conservative, the IPCC decided to not include this aspect in their AR4 report. Unfortunately, the result is a significant under-appreciation of the loss of continental ice at the poles due to global warming. To address this, Vermeer and Rahmstorff (2009) have devised a semi-analytic method which captures 98% of the variance in ice volume vs global temperatures, and use it to predict sea-level rises for the coming century using current and historical data. It shows sea-level rise of 3-6 feet by 2100 (depending on anthropogenic emission scenario), which is 3 times the IPCC AR4's conservative calculation (see 3rd panel graph below). Baffin Island, also in the Arctic and the 5th largest island on Earth, has lost 50% of its ice cap in the last 50 years. Globally, glaciers worldwide are in rapid retreat (see graph below right - sorry for the poor reproduction!). See this video of congressional testimony which contains a nice animation of the GRACE data on where and when ice is being gained and lost on Greenland. This 2011 paper in GRL shows excellent agreement between two ice volume measures: GRACE, and ice accumulation vs perimeter loss. They both show accelerating ice loss and strong rising sea level predictions for this century. However, a new paper published in Nature (Sundal et al. 2011) uses satellite measurements to show that once a critical level of melting is exceeded, the drainage under glaciers transitions to a more efficient mode and glacier speed slows. It will be interesting to see this new work included in future modelling of Greenland ice loss, as it is the major determiner of sealevel rise as global warming accelerates. Also contributing to Greenland and other polar ice loss is the darkening of surface ice. The darkening can be caused by partial melting of snow flakes, changing their geometry and reflectivity, and/or to the accumulation of dark pollutants and soot from the growing number of wildfires as climate warms. A short video on the albedo issue here.

A key point to make is that simplistic arguments I've heard from denialists about Greenland taking millenia to melt make the assumption that the ice stays in place. High altitude ice is certainly colder and more stable than low elevation ice, yet what we see is meltwater de-stabilizing the deep ice/continental interface and speeding the breakup and transport of ice to the oceans. This has been seen for many years now, described by polar scientists in this 2013 video (5 min). This study, published in Nature: Climate Change in 2012, shows indeed that Greenland is more sensitive to losing it's entire ice cap than previously thought. We are already close to the temperature levels which will completely melt Greenland over the next centuries, even if CO2 levels are brought back down. Hansen and Sato (2012) provide a good update on Greenland and Antarctic ice loss in a "business as usual" scenario into the future, and review the recent papers, arguing that simple linear extrapolations of past ice loss are a very likely underestimate of this non-linear process. While sea level rise by 2100 is still highly uncertain, the "scientific reticence" approach (Hansen and Sato 2012) of the IPCC 2007 AR4 should not be relied on for comfort, and sea level rise of over a meter or two are quite possible or even likely, given that past sea level rise was almost all due to thermal expansion (linear), while future rise will see a major additional contribution from continental glacier disintegrations..

Another positive feedback not included in climate models is the darkening of Greenland and Arctic ice from increasing wildfires as increasing drought (also consistent with climate modelling) dries out Northern Hemisphere forests. Indeed, in 2012, wildfires were especially bad and studies show the resulting ash was able to briefly melt Greenland ice over the entire continent, even the normally permanently frozen highest elevation interior (Kaitlin et al. 2014 in PNAS).

Looking to the future, finds that even the northern ice cap of Greenland - thought to be safer from melt due to being colder - was in fact especially vulnerable, and melted during the last interglacial which exhibited temperatures as high as we'll see in the 21st Century. The reason seems to be melting due to warm water un-anchoring the ice-sheet's contact with topography in the shallow ocean there, removing the buttressing effect. (Born et al. 2012)

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