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Tim Flannery: Up to 2005 it looked as if there'd still be some sea ice by the end of this century in the Arctic. But in 2005 the sea ice started to melt away at about four times the rate of previous years, and that's now continued. And this year, the start of this summer has been just terrifying. The sea ice is melting away at about 6,000 square kilometres greater rate per week than last year. And if this summer follows the trajectory of the last few summers, we stand to lose about half the remaining sea ice by the end of this northern summer. And that is putting us on a trajectory to an ice-free Arctic within five years or so.

Alexandra de Blas: And what are the implications of that?

Tim Flannery: Well, the implications are profound because once the ice is gone the surface levels of the Arctic Ocean will start warming quite rapidly, because it's a dark surface and it absorbs light energy and turns it into heat energy. So the thermal balance of the area around Greenland will change, we'll start getting warming, so we can expect an accelerated rate of melt in Greenland. And that ice cap has enough water frozen in it, were it all to melt, to raise sea levels by six or seven metres. So that's one thing.

The second thing is of course that the entire climatic zonation of the northern hemisphere is held in place by the thermal gradient between the pole and the equator. That's why we have deserts where we have them in the northern hemisphere, and we have forested areas where we have them and tundra where we have them. And when I look at the melting tundra, the advance of the forest northwards...Greece and its forest fires that look like that area's becoming hostile to the sort of vegetation. I think we're seeing the early stages of a shift in that zonation. Once the ice melts away entirely and we get a rapid warming of the Arctic Ocean, that's when you'll see those sorts of changes potentially start shifting much more quickly.

Alexandra de Blas: If the sea ice is gone, say, within five years, how rapidly will we expect the Greenland ice cap to start melting?

Tim Flannery: Again, it's just not possible to answer that question, principally because ice doesn't just melt away as you might imagine an ice cube sitting on a bench would. It melts away, in part at least, by large-scale collapse. So ice shelves tend to collapse into the ocean and then fragment and then melt much more rapidly than they may otherwise do. And that sort of collapse is just impossible to model. We've seen it occur in the Antarctic Peninsula with the Larsen B ice shelf, but it is just impossible to model so we don't know. But people are now I think quite realistically talking about sea level rise, if nothing's done, of several metres this century.

Alexandra de Blas: Which will be astounding.

Tim Flannery: That will mean probably hundreds of millions of people displaced, a lot of the world's best agricultural land lost, some of the world's great cities threatened or under water, places like Shanghai and Amsterdam and London and so forth. Amsterdam's about two-and-a-half metres under water as it is, just held up by the dykes. And Singapore and so forth. So the changes, if you want to sum them up, that's the end of our global civilisation. The stresses that would be placed upon the global political system and economic system would be such that it simply couldn't endure them.