What's the impact of rising sea levels?

As the floods in Pakistan are highlighting, climate change is set to alter the distribution of water across our planet in a dramatic way. One of the most widely covered aspects of this is rising sea levels. Peter Haynes, the news that sea levels are projected to rise, in the US, by 30cm in the next 30 years doesn’t seem that much. Why is it such a problem?

Chris - Peter, let's cross over to you. We've all seen the footage of what's happened to Pakistan. Climate change has had the finger pointed at it for what's happened there with flooding. Other countries as well are seeing very dramatic shifts in weather and our own country, the UK, we've seen a very radical departure from what we regard as normal summer temperatures this year and in recent years. So let's just consider climate change for a minute. One of the things that people often talk about in the context of climate change is what will happen to sea levels. And some of the predictions are only about 30 centimetres of sea level rise in the next 30 years. This question says, why is only 30 centimetres in 30 years such a problem?

Peter - I think the key thing here is that whilst sea level rise of a foot doesn't seem to mean very much if you're on the beach or something, right, we have to think of this in the context of severe extreme events and any systematic rise in sea level is going to increase the likelihood and the frequency of extreme flooding events. So it's not so much the fact that the average by itself has gone up. It's the fact that those high water events, the times for example when tides and the weather reinforce each other, those leading to dangerous levels of water rise are going to become more frequent.

Chris - A lot of people also point to Antarctica. And the fact that if that melts that's going to have a really significant impact, and Greenland of course, because that's ice that's not already in the water and so it's not floating and it will therefore directly contribute to a sea level rise, unlike the Arctic where the ice is already displacing water. So if that melts, the water just redistributes, but it doesn't actually mean there's a change in sea level rise.

Peter - That's right. It's the melting of ice on land that will have the most severe implications. Just in the last week or so, I think I read a newspaper headline the other day that it was going to be inevitable that the Greenland ice cap was going to be lost to a large extent. But I think another point to think about here is that melting of ice caps isn't the only effect that's going to give sea level rise. Also, just the fact that water expands when you heat it up is going to make an effect, right? So these things have to be considered together. There will inevitably be sea level rise, whatever happens to the Antarctic ice shelf or Greenland in the next 50 years, simply because of thermal expansion.

Kathryn Harkup - Something I was going to ask also about once all of this ice disappears from the land surface, do we know what is underneath that that's been trapped in? I've heard stories of methane gases that would be released after thaws and so on. So is there any concern about once the ice is gone what is left behind?

Peter - Certainly there is methane trapped in the sea bed. Increases in temperature and melting will potentially release it. Methane is a greenhouse gas, it traps radiation near the earth's surface, it'll increase the overall temperature. There are subtle differences with the way it works from carbon dioxide. Another effect that I could mention is this idea of what scientists called albedo, which is reflecting radiation. This is relevant actually to mountain glaciers as well as to the Arctic sea ice. Currently, where you have ice, you're reflecting radiation back so you don't get so much heating as soon as you remove the ice. And actually another effect here is having soot on the ice, for example, which might come from wildfires and things, particularly in mountain areas, that reduces the reflectivity which means you get more radiation absorbed and more warming. So there are quite a few different feedback effects that might have to be considered as important.

Chris - And albedo is quite different from libido...