20120813_R4

Source: BBC Radio 4: Today Programme

URL: http://news.bbc.co.uk/today/hi/today/newsid_9744000/9744378.stm

Date: 13/08/2012

Event: "Arctic ice seems to be melting faster than previously thought."

People:

• Evan Davis: Presenter, BBC Radio 4 Today programme
• Seymour Laxon: Professor of Climate Physics, UCL

Evan Davis: Arctic ice seems to be melting faster than previously thought. Preliminary results - and I should stress preliminary - from a European Space Agency satellite that's been measuring the thickness of Arctic ice imply that if the observed trend continues, the Arctic could be ice-free in the summer by the end of this decade, which is remarkably soon. Seymour Laxon is from the Centre for Polar Observation and Modelling at UCL in London, and is with us in the studio. Good morning to you.

Seymour Laxon: Morning.

Evan Davis: What was the, sort of, projected trajectory before these preliminary results came out?

Seymour Laxon: Well, the history of the prediction of when the Arctic might be ice-free is quite interesting, because about ten years' ago, the prediction was that we'd have an ice-free Arctic by about the end of this century. Then, in about 2007, satellites that actually measured the area of the ice - not the thickness, like the satellite we have - showed that we reached the level of ice that we weren't really expecting until 2030 or 2040. So at that point, the modellers went back, took account of this data, and came up with a prediction of about 2030, 2040. What the new data show is that we've got a very strong decline, not just in the extent but also in the thickness. And by combining the data from CryoSat - which is the satellite we work with - with a NASA - an American - satellite called ICESat, which took some measurements earlier on in this decade, we can see this very strong change in thickness just happening in this decade.

Evan Davis: So you've actually - it's not that you've got - that we'd misjudged how much there was there, in the first place. You've actually seen it melting, effectively. You've got two data points that are really quite different.

Seymour Laxon: That's right. I mean, we know that the area of the ice has been going down for about 30 years. But what's new is we're actually able to measure the thickness, from which we can get the volume, which actually gives you the total amount of the ice in the Arctic, not just how much area is covered.

Evan Davis: Right. How much ice is there in the Arctic? I mean, we've often heard about the Greenland ice, for example, being a potential threat to sea levels, and all of that. But how much ice is there in the Arctic?

Seymour Laxon: Well, there's about - right now, there's about 4,000 - sorry, there's about 4 million square kilometres' coverage. But that grows and shrinks as the winters go on every - expands and contracts. In terms of volume, what we were getting at the end of last summer, so after the melt season had happened, we were looking at a number of about 7,000 cubic kilometres.

Evan Davis: Right. What about the Greenland ice? Are you monitoring that as well, is that something you're watching?

Seymour Laxon: We're not - we don't work on that directly in UCL - I have colleagues who work on that. So that, also - there were some recent results from NASA, about a month or so ago, where we saw that apparently from satellites, all of the Greenland ice sheet was melting for a few days.

Evan Davis: Sorry, how do you mean - for a few days? It was, it was -

Seymour Laxon: Well, at the height of summer - because that's when we're really looking at - that's the point at which we - the maximum degree of melt that we can see in any one year.

Evan Davis: How confident are you of these figures? Because we've had, you know, data before, and we've realised that it wasn't quite right, and all these kinds of things. What - how much confidence should we attach?

Seymour Laxon: Well, as far as the CryoSat measurements go, we've been able to validate our measurements using both - two sets of aircraft, a European Space Agency aircraft, a NASA aircraft - and also some moorings in the ocean underneath the ice, which measure how thick it is. So we know that CryoSat is probably making measurements accurate to about 10 centimetres in thickness, which is good enough to say what our decline in volume is. There's a little bit less certainty about the NASA measurements, because we have less measurements on the ground to check them, but we're reasonably confident those are good. In terms of the prediction, one has to be careful, of course, in using the past as a guide to the future, as you know. But we can say that the trend we're seeing now - if that continues, only if that continues - that holds the prospect that we might see an ice-free Arctic... only during the summer, only in the peak of the Arctic summer, for perhaps even only one day...

Evan Davis: ... but the ice will have disappeared. Yeah.

Seymour Laxon: And what we really need to do, actually - to answer this question - and the next step really, is to get this data into the models that can do a really proper forecast, just like the weather forecast models we have and we use for everyday weather.

Evan Davis: Seymour Laxon, thank you very much.