July 2012 Greenland Melt Extent Enhanced by Low-Level Liquid Clouds

Increased glacier melting due to global warming can have serious global consequences. Run-off from this rise in melting contributes to sea-level rise around the world which puts communities or even whole countries at risk of permanent flooding in the future. In July of 2012 the Greenland ice-sheet (GIS) experienced an enhanced period of melting that had not been observed in past years. Using various methods to record the melting and local temperature it was determined that low-level liquid clouds were the main factor causing the decrease in the ice-sheet (Bennartz 2013). These clouds were of a particular thickness that allowed them to trap heat while allowing in enough solar radiation to heat the surface of the glaciers. These clouds are part of a positive feed-back loop in which global warming has already contributed to ice melt in the arctic, putting more water into the atmosphere which contributes to the low-level liquid clouds. These clouds then further enhance the melting contributing to more of these types of clouds. Using multi-channel microwave measurements, the researchers were able to determine that these clouds can cover up to 20-50% of the arctic (Bennartz 2013). –Andrew Walnum 

Bennartz, R., Shupe, M., Turner, D., Walden, V., Steffen, K., Cox, C., Kulie, M., Miller, N., Pettersen, C., 2013. July 2012 Greenland melt extent enhanced by low-level liquid clouds. Nature 496, 83-86.

                  R. Bennartz and his colleagues used many different methods for observing melting and the low-level liquid clouds. Ground-based data were collected using “infrared, microwave, radar and lidar remote sensing observation” as part of the ‘Integrated characterization of energy, clouds, atmospheric state, and precipitation at Summit’(ICECAPS). These data were then compiled to plot the amount of ice melt for the Greenland icesheet. Based on cloud data the researchers were able to develop a model to explain the effects of low-level liquid clouds.
                  The results revealed that on days when low-level liquid clouds were present temperatures were able to rise to or above 0 oC. Melting occurred on days when clouds were absent the GIS did not experience surface temperatures above melting temperature. Using a model which takes into account temperature, specific heat, height, air density, infrared flux, and time, the researchers were able to conclude that it was in fact low-level liquid clouds contributing to the rise in temperature and ice clouds. However, the low-level liquid clouds do not always contribute to rising temperatures. The thickness of the clouds determines how much solar radiation is reflected or trapped. When the clouds are thin enough they allow more solar radiation to pass through to the earth while still radiating the heat downwards. When this occurs, surface temperatures are essentially the same temperatures as the clouds.

                  The helps give important insight into future models of climate change in the arctic. The results from this paper show how important low-level liquid clouds are to surface energy balance (the amount of infrared energy that hits the GIS’ surface and is retained or reflected.) Modern climate models do not take into account how changes in the atmosphere will contribute to cloud cover which inhibits the models from recognizing feedback loops that might further contribute glacier and ice-sheet melting in Greenland.

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