Global warming is causing increased melting in polar regions. How do we know this? Because we can measure changes in mass balance (or the amount of ice that has melted) using space-geodetic techniques that detect variations in the Earth's gravity field and changes in ice height. How fast are Antarctica and Greenland melting and how is such melting contributing to rising sea level? There is the opportunity to study all aspects of the effects and ramifications of climate change, from measuring sea level variations using satellite altimetry and tide gauges, measuring with GPS the rebound of the Earth's crust caused by the melting of past ice sheets, monitoring mass balance changes through GRACE observations of gravity changes and/or assimilating all these observations to develop new models of past and present ice sheets for Greenland, Antarctica and North America. This exciting area of research has direct implications for understanding the present-day effects of climate change.