Ed Waddington is a geophysicist who studies problems that arise when geologists try to interpret paleoclimate records from polar ice cores. He has studied ice in Greenland, Alaska, Antarctica, and also, extraterrestrially, on Mars. He and his students measure surface velocities and strain rates on ice sheets using a variety of methods, including GPS. They use ice-penetrating radar to detect layering within the ice, since ice found at different depths may have come from very different places on the surface of the ice sheet, depending on that ice sheet’s particular history. They combine these data with computer models, to derive the ice flow patterns at depth. With all of this information, they can piece together what the climate was like hundreds or thousands of years ago.