Our new study reveals that under warm and wet conditions, atmospheric heat can melt the lower 1/3 of the Greenland ice sheet elevations more than under sunny conditions. This was especially so during the 2012 heat wave when a record warm North America loaded the air with heat and moisture that drifted to Greenland.
We recorded the largest ever observed daily and annual surface melt rates on Greenland under PROMICE. The 8-11 July, 2012 heat wave produced 0.9 m (3 ft) of ice melt for a yearly total of 8.5 m (28 ft), actually 9% less than the 2010 annual value of 9.2 m (30 ft). The peak daily melt rate was 0.28 m (11 inches) occurred on 11 July. To capture such high melt rates, we use a 12.4 m (40 ft) long ruler.
A persistent air flow that drove air up and over west Greenland prevailed for 6 summers (2007 to 2012), parts of 2015, and in other years. This is the same kind of “atmospheric river” that can replenish California’s moisture deficit and cause flooding. In the case of Greenland, if it’s summer and air temperatures are high enough, there will be no snow, just rain and atmospheric heat delivered to the ice surface can do untold damage to the surface.
The study decomposes the ice melt energy into contributions. Together, atmospheric heat and condensation delivered more energy to the lower elevations of the ice sheet than absorbed sunlight during pulses in July and August 2012. It’s counterintuitive that under cloudy conditions there can be more melting, especially because the surface is so dark in this lower 1/3 of the ice sheet elevations. It goes to show that the ice sheet melt does not get a break just because the sun is blocked.
Climate models under-represent this effect, by our estimate by a factor of two, and with the frequency of warmer air masses driven over Greenland expected to increase with climate change (Collins et al., 2013), the impact of atmospheric heat and condensation will probably bring Greenland ice melt loss faster than forecast.
- Collins, M., R. Knutti, J. Arblaster, J.L. Dufresne, T. Fichefet, P. Friedlingstein, X. Gao, W.J. Gutowski, T. Johns, G. Krinner, M. Shongwe, C. Tebaldi, A.J. Weaver, and M. Wehner, (2013), Long-term Climate Change: Projections, Commitments and Irreversibility. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
- Fausto, R. S., D. van As, J. E. Box, W. Colgan, P. L. Langen, and R. H. Mottram (2016),The implication of nonradiative energy fluxes dominating Greenland ice sheet exceptional ablation area surface melt in 2012,Geophys. Res. Lett., 43, doi:10.1002/2016GL067720.