Greenland is the world's largest island and contains the second largest glacier on Earth with a surface extent of 1.75 million km2, containing enough water to raise global sea level by approximately 7 meters. As a consequence, Greenland is important with regard to Earth’s climate as it provides cooling for the planet, water storage, and, from a hazard perspective, because it produces large quantities of icebergs.
Why do we care about monitoring the extent of surface snowmelt in Greenland? Because wet (melting snow) and dry snow have very different physical properties, although they may look similar. Greenland is very sensitive to changes in Earth's climate, such that even a small rise in its surface temperature will increase the extent of surface snowmelt. This decreases the amount of solar energy reflected back to space (as wet snow absorbs more of this energy), which, in turn, will increase the total energy absorbed by the Earth. Recent studies also show that melting snow enhances sliding of glaciers as surface melt water seeps down to the ice-bedrock interface. Furthermore, increased melting liberates water that can then freely evaporate; this may increase cloud cover, which is associated with its own complex set of climate feedbacks.
Space-borne microwave sensors, such as the Special Sensor Microwave/Imager (SSM/I) radiometer, can “see” through clouds and do not require solar illumination. They are also very sensitive to the presence of liquid water within the snowpack and, therefore, can be used for mapping melting snow in Greenland.
We used SSM/I data collected between 1979 and 2006 for mapping melting snow over the Greenland ice sheet. We compared our results with ground-based measurements collected by automatic weather stations deployed in Greenland, and with surface temperature data derived from global models and with data from other satellites. By means of satellite data, we were able to identify an extreme melting event at the end of June, 2002 where, for the first time in 28 years, melting occurred at locations in inner Greenland at high altitudes. During the same year, over 80 % of the entire Greenland ice sheet surface experienced at least one day of melting; this corresponds to an area the size of France, Spain and Italy put together. Results also suggest that the area experiencing at least one day of melting has been increasing since 1992 at a rate of 35000 km2 per year (~2 % of the entire Greenland surface), meaning that every year an area equivalent to the state of Maryland would be subject to new melting.
A long-term analysis for the period 1988 – 2006 shows that 2006 ranked seventh or fifth in terms of duration and extent, depending on the frequency, within the study period. Melting anomalies for 2006 are consistent with results regarding snow loss, altitude or surface temperature changes from other satellites mission, such as GRACE., ICESat and MODIS. Melting duration increased during 2003 - 2006 with respect to the period 1988 – 2002 in particular in the northeast and southwest part of Greenland, where most of Greenland glaciers are retreating and a significant snow loss is observed.
References:
Tedesco, M. (2007), Snowmelt detection over the Greenland ice sheet from SSM/I brightness temperature daily variations, Geophys. Res. Lett., 34, L02504,doi:10.1029/2006GL028466, January.
Tedesco, M. (2007), 2006 updated snowmelt over the Greenland ice sheet from space-borne microwave brightness temperatures, submitted to EOS Transactions, AGU.
Tedesco, M. (2007), An improved technique for snowmelt detection (1979–2006) over the Greenland Ice Sheet using microwave brightness temperature daily variations, EGU Meeting, Vienna, Austria, 15-20 April.
Link to article: http://jcet.umbc.edu/news/is_greenland_melting.html
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