It is a difficult task to estimate the mass loss of the large ice sheets, Greenland and West Antarctica.
Recent modeling, where isostacy due to load changes is incorporated (in a better way than before) change these estimate greatly.
For the period of GRACE measurements (2002 – 2008), the mass loss per year changes from earlier estimate to the new estimate as shown below:
| Earlier estimate Mass loss (Gt/a) | New estimate Mass loss (Gt/a) | |
| Greenland | 230 | 104±23 |
| West Antarctica | 132 | 64±32 |
The difference here is almost 100 Gt/a (giga-tonnes per year) for Greenland, and 40 Gt/a for West Antarctica.
This means that the large ice sheets contributed less to the rise in sea level than previously thought. The difference is ascribed to thermal expansion (at least for now).
Details can be seen in the article by Wu et al. (2010) in Nature Geoscience (needs subscription, so I have only seen the abstract and the news about the results): http://www.nature.com/ngeo/journal/v3/n9/full/ngeo938.html
Then we just need to wait and see whether new models change these numbers even further, and in which direction :-)
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