Using RADARSAT synthetic aperture radar data, we have mapped the flow velocity over much of the Greenland ice sheet for the winters of 2000/01 and 2005/06. These maps provide a detailed view of the ice-sheet flow, including that of the hundreds of glaciers draining the interior. The focused patterns of flow at the coast suggest a strong influence of bedrock topography. Differences between our two maps confirm numerous early observations of accelerated outlet glacier flow as well as revealing previously unrecognized changes. The overall pattern is one of speed-up accompanied by terminus retreat, but there are also several instances of surge behavior and a few cases of glacier slowdown. Comprehensive mappings such as these, at regular intervals, provide an important new observational capability for understanding ice-sheet variability.

It has been widely hypothesized that a warmer climate in Greenland would increase the volume of lubricating surface meltwater reaching the ice-bedrock interface, accelerating ice flow and increasing mass loss. We have assembled a data set that provides a synoptic-scale view, spanning ice-sheet to outlet-glacier flow, with which to evaluate this hypothesis. On the ice sheet, these data reveal summer speedups (50 to 100%) consistent with, but somewhat larger than, earlier observations. The relative speedup of outlet glaciers, however, is far smaller (<15%). Furthermore, the dominant seasonal influence on Jakobshavn Isbrae's flow is the calving front's annual advance and retreat. With other effects producing outlet-glacier speedups an order of magnitude larger, seasonal melt's influence on ice flow is likely confined to those regions dominated by ice-sheet flow.

Previous studies in Greenland show that retreat of tidewater glaciers may be linked to recent increases in ice loss, raising Greenland's contribution to sea level rise. We examined ice front changes of 203 tidewater glaciers, land‐terminating glaciers, and glaciers terminating with ice shelves to understand Greenland glacier behavior over three periods: 1992–2000, 2000–2006, and 2006–2007. We observed synchronous, ice sheet–wide increases in tidewater retreat during 2000–2006 relative to 1992–2000, coinciding with a 1.1°C increase in mean summer temperature at coastal weather stations. Rates of retreat for the southeast and east slowed during 2006–2007 when temperatures were slightly cooler than the 2000–2006 average. Our work suggests that regional Greenland tidewater retreat responds strongly to climate change, with higher temperatures corresponding to increasing retreat, and helps confirm a link between ice thickness, velocity, and ice front position.