" A satellite study of the Greenland ice cap shows that it is melting far faster than scientists had feared - twice as much ice is going into the sea as it was five years ago. The implications for rising sea levels - and climate change - could be dramatic. Yet, a few weeks ago, when I - a Nasa climate scientist - tried to talk to the media about these issues following a lecture I had given calling for prompt reductions in the emission of greenhouse gases, the Nasa public affairs team - staffed by political appointees from the Bush administration - tried to stop me doing so. I was not happy with that, and I ignored the restrictions. The first line of Nasa's mission is to understand and protect the planet. This new satellite data is a remarkable advance. We are seeing for the first time the detailed behaviour of the ice streams that are draining the Greenland ice sheet. They show that Greenland seems to be losing at least 200 cubic kilometres of ice a year. It is different from even two years ago, when people still said the ice sheet was in balance. Hundreds of cubic kilometres sounds like a lot of ice. But this is just the beginning. Once a sheet starts to disintegrate, it can reach a tipping point beyond which break-up is explosively rapid. The issue is how close we are getting to that tipping point. The summer of 2005 broke all records for melting in Greenland. So we may be on the edge.