Science Interviews

Interview

Tue, 9th Sep 2014

Is the Arctic icesheet shrinking?

Eric Wolff, University of Cambridge

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Global warming is often in the news but this week the Daily Mail ran an article withBathymetric map of the Arctic Ocean the headline: ďMyth of ARCTIC meltdown: Stunning satellite images show summer ice cap is thicker and covers 1.7million square kilometres more than 2 years ago.Ē

The article showed a graph charting a steady decline in ice coverage over the last 10 years and then a rebound, where ice cover appears to have doubled in the last two years. Professor Eric Wolff from the University of Cambridge explained to Ginny Smith that there's more to this story... 

Eric - So, weíre talking about the ice thatís frozen on top of the Arctic Ocean and every year, at the end of winter, there's a maximum amount of ice that covers most of the Arctic Ocean.  Most of what you'd see between Siberia or in Canada or Greenland.  And then that retreats by somewhere between 50% and 70% at the moment during each summer.  So, it should reach its minimum actually in a few daysí time.  So, what they're looking at is the average amounts of ice in August.  So, pretty close to a minimum and thatís clearly trending downwards quite rapidly by around about 10% every decade.  But it does vary from year to year because of various natural reasons and 2012, which is the year that the Daily Mail picks on - 2 years ago, happened to be a really low year. And  2014 actually looks very similar to 2013.  So, if you take any 10-year period in the record that I've got in front of me, then it just looks like a lot of noise actually.  It just looks as though itís going up and down.  But as soon as you look at the whole 37 years that weíve got satellite data, itís very obvious that the sea ice is decreasing.  2014 is still lower than any year between the beginning of the satellite record in 1979 and 2006.  So, itís certainly not a high sea ice year.

Ginny -   So, itís not really that ice is recovering as such, itís just sort of natural fluctuations.

Eric -   Itís natural fluctuations, just as you wouldnít expect asyou come into summer, you donít expect every day to be warmer than the one before.  Itís the same thing.  As weíre losing the ice slowly as due to global warming, and particularly to Arctic warming, you donít expect every year to be lower than the one before.  There are lots of meteorological factors that can affect it.

Ginny -   So, this doesnít shed any doubt in your mind on the idea of global warming is happening and it is having these effects on the Arctic?

Eric -   No, none at all.  I'm afraid there isnít really good news here.  the amount of carbon dioxide in the atmosphere is continuing to increase pretty rapidly.  That inevitably means that temperatures will warm.  It won't be uniform around the globe and it won't be the same every year, sometimes more heat goes into the ocean, sometimes more goes into the atmosphere.  But I'm afraid, as the Arctic warms, the ice does melt.  

Ginny -   So, what is it thatís causing these natural fluctuations within that kind of downwards trend?

Eric -   Well, itís mainly due to the meteorology in the Arctic which determines how the ice moves around because the amount of sea ice thatís left is not only a function of the temperature of the ocean in the atmosphere, but itís also a function of where the ice actually gets moved to by the winds.  So for instance, in 2012, part of the course was that just before, some time in August, there was a big storm at a time when the ice was already quite thin.  And that big storm just broke the ice up and moved it all southwards into an area where it could melt.  And that wasnít the complete reason.  There are lots of things that push the ice around and put it in one area or another, somewhere thatís colder, or somewhere thatís warmer.  But that does mean there can be quite big variations from year to year, actually, especially at this point of the year when the ice is already quite thin.

Ginny -   So, if there are so many factors going on, how do you go about making predictions about how the ice will be affected?  I mean, there was this prediction from Al Gore that it wouldíve all gone by now.  How did he get that so wrong?

Eric -   He was quoting a study that said that it might have disappeared by now and he made it sound so he thought it would.  But he got a little over enthusiastic I'm afraid.  So, what you do, I'm afraid the only way you can predict the future because we haven't seen it yet is by using models.  Those models are based on the best physics that we have of understanding both how the climate works and how the ice responds to the climate.  And so, all you can do is to run these models with and without changing levels of carbon dioxide, and what the models are saying. itís a whole range of models from different countries, is that around this time of year, the ice will virtually have gone, that thereíll be a little bit of ice here and there, but a few percent only.  The ice will virtually have gone by 2050.  So, itís not this year, itís not next year, itís not the best bet, but itís not going to come back again either.  So, some time within the next few decades.

Ginny -   So, you're putting all this kind of data that you have into a computer model and sort of simulating the future.  But different people are still making different predictions.  So, how can the public decide who to trust?

Eric -   Theyíre all making predictions that the ice is going to reduce.  If you now run the models through the last 30 or 40 years, they're actually doing pretty well.  They donít get quite as big fluctuations weíve seen, but they're not doing too badly.  But all the models would predict that the ice is going to reduce.  Exactly, when there's no ice in September differs from model to model.  If you think that we need to take action, you'll still think whether itís 2040 or 2070, and if you donít really care about it, then you'd still think you donít care about it.

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