Ancient air in Antarctic ice

11 June 2019

Interview with 

Robert Mulvaney, British Antarctic Survey

ICE-CORE

An ice core segment extracted in Antarctica

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Climate change is considered to be one of the most serious threats facing us in the coming decades. So understanding why things are changing, and how they’ve changed in the past is critically important. Travelling to the extreme cold and carrying out science in places that would freeze your fingernails off has its benefits, as Adam Murphy learned when he took a trip out to the British Antarctic Survey, to speak with Robert Mulvaney...

Adam - Sometimes it doesn't matter if it's cold, even extremely cold, there’s still science to be done. And there's lots of science being done in Antarctica. A lot of it has to do with ice cores, cylinders of ice taken out of the Antarctic ground. But to learn exactly what these tubes of ice are for, I spoke to Robert Mulvaney from the British Antarctic survey who has spent 25 seasons in Antarctica...

Robert - I'm a glaciologist and in particular I drill ice cores. And what I'm looking at is climate and the atmosphere evolution over many thousands of years. So if we drill into the ice we’re drilling further back in time so in the polar regions you essentially get very little snow melting at the surface. As the snow falls it just builds up year on year and eventually compresses to the point where the layers are really really thin near the bed, but the ice might be 2 to 3, maybe 4 kilometres thick in places. If I go and sit in a camp on the surface and then set up a drill rig and drill down into the ice, I'm drilling further and further back into the past. Now the ice remembers  something about the climate and what we do is we drill these cores of ice, we bring them back to the lab here and we measure things in the ice that tell us about the climate. But also locked in the ice are tiny bubbles of air, and these bubbles of air are the actual atmosphere of the past. It's the only place on Earth that still has an archive of past atmosphere so as we drill deeper into the ice we're able to recover the climate record from the ice itself, and then a record of the atmosphere from the bubbles trapped in the ice.

Adam - To learn exactly how they keep the ice and what they do with it, we donned our jackets and wandered into the freezer

...Oh, that is noticeably colder.

Robert - So I've just brought you into the cold laboratory here at BAS. We keep this room at about -25 and this is where we process the ice. So what we take is the column of ice that we've collected in Antarctica and we cut it into the sections that we're going to use for analysis. What we've got here, it's got an arrow on it to say which way up it is. It's just a column of ice, and every column of ice looks exactly the same, so we have to be able to identify it when we get back here. It's got the top at this end.

Adam - Is that the newest ice at the top?

Robert - Exactly. The bit nearest the surface is the youngest ice, the bit nearest the bottom is the oldest ice. We know at this site the ice at the bottom is likely to be something like 140,000 years old. So if you imagine we’re in a warm  period at the moment, we could go back 140,000 years ago you're in the ice age before last, so this is ice age two. At the bottom of the core this ice will be 140,000 years old or thereabouts.

Adam - Back in the comfort of a nice warm office waiting for my jeans to come back to a normal temperature, I asked about the human effects on the climate...

Robert - If we look at the greenhouse gases, what we see is through all of the cold period, so all of the glacial periods, the level of carbon dioxide in the atmosphere is 190 parts per million or thereabouts. If we go into a warm period the number is about 270 parts per million. You get all the way up to about the 1770s and suddenly it starts to rise, and it starts to rise and continues to rise until you get to the level we see today in the atmosphere, which is about 410. And around about the 1770s was when the steam engine was invented. And almost as soon as the steam engine was invented the industrial revolution kicked off, we started burning more and more fossil fuels and almost instantly the atmosphere responded and carbon dioxide began to rise. The level of 410 we see today, we can't see anything like it in the last 800,000 years.

Adam - Now I remember reading somewhere that you can see traces of lead in the ice from when we used to drive cars, is that true?

Robert - Yes, that's true. So almost anything that's emitted into the atmosphere in terms of pollution, if it remains in the atmosphere long enough to be taken up and carried by wind and circulation to the polar regions and deposited in snow, then there's a chance that we can measure it. It's very difficult to measure. If you imagine the amount of lead we measure is something like a grain of salt in an Olympic swimming pool, that's a sort of concentration we were trying to measure. What we are able to show is that the lead in the atmosphere had been rising again since the point where cars started to use leaded petrol. Now there was a fairly low level of lead which supports lead in petrol and the lead began to rise quite quickly. Now up until that point, I think the oil industry has always claimed that most of the lead that you see in the atmosphere came from natural sources, it came from things like volcanoes. But when we showed them what the lead looks like in the polar regions where you get this very low level and then a rise just at the point when lead was put into petrol. They said okay, we believe it, we understand. Lead was taken out of petrol and now the lead is coming back down to the levels that we saw before it was ever introduced into petrol. So in a sense the atmosphere has cleaned itself up. There's much lower levels of lead in the atmosphere and we would have seen in the 70s and it's down to almost its background level.

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