Greenland is melting, but how fast?
The IPCC (2007) report explains that if the Earth's mean global temperature reaches more than 1.9oC above pre-industrial temperatures, we can expect the Greenland Ice Sheet to loose mass through melting faster than it is replaced by precipitation. If these conditions were to be maintained for 1000s of years we expect:
The mean global temperature is currently about 0.8oC above pre-industrial temperatures and rising at about 0.18oC per decade. These predictions are based on 3D models of the ice sheet (Figure 1; Alley et al., 2005), with specific atmospheric carbon dioxide concentration scenarios (e.g. Gregory et al., 2004).
Figure 1: The modelled evolution of the Greenland Ice Sheet suggests complete elimination over the next 3000 years for a scenario with CO2 concentration at 1000 ppm (equivalent to 7oC warming over 500 years). source: Alley, R.B., Clark, P.U., Huybrechts, P., and Joughin, I., (2005). Ice-sheet and sea-level changes, Science, 310(5747): 456-460. 10.1126/science.1114613.
As outlet glaciers speed up (and slow down) they deliver more (and less) ice into the oceans. Dramatic changes in glacier speeds have been observed in recent years, but are not yet well understood (e.g. Nick et al., 2009). Furthermore, current models of the Greenland Ice Sheet future evolution are unable to produce these dynamic changes. Better knowledge of the mechanisms controlling the outlet glaciers is required to improve this limitation.
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