Planet Earth - Sniffing the Atmosphere

Dave -   Predicting how the Earth's climate is likely to change is one of the toughest challenges facing science, one that as we know is not without its controversies.  To build accurate simulations of the climate, scientists need raw data and Planet Earth podcast presenter Richard Hollingham has been to Scotland to meet researchers sniffing the air.

Richard -   I've come to a Scottish hillside, about 10 miles north of Dundee and I'm standing underneath a very tall tower.  It's actually called the Angus Tall Tower.  It's because it's in Angus and it's a tall tower.  It's a TV tower covered in transmitters and we're surrounded by fields of sheep, and behind me heather moorland.  John Moncrieff from the University of Edinburgh is with me.  Now you're not interested in the TV transmitter.  You're interested in the instrument, right at the top of this tower, sniffing the air.

John -   That's right, Richard.  It's not so much in the instrument, it's more just a tube.  We actually have a long tube which goes from the very top of the tower, about 220 metres up, and we sample air down this tube into some analysers which we have in a cabin just in front of us.

Richard -   What are you trying to measure here?

John -   I'm really trying to measure very accurately the greenhouse gas concentrations of the air as the air moves past the tower.  So I'm interested in the concentration of the three big greenhouse gases:  carbon dioxide, methane and nitrous oxide.

Richard -   Okay, so you've got this tube, almost like a hose pipe, I suppose, coming down the tower, through this cabling duct and then behind us, through this door.

John -   That's correct, yes.  Let's go inside and see the instruments.

Richard -   So you've got a stack of shelves with a computer on one, a mass of tiny little tubes on the other and occasionally, it's emitting a bit of a belching sound, and you're measuring greenhouse gases now?

John -   We're trying to build up a picture of how the greenhouse gases change over time in this particular location.  The reason we're on a tall tower - we take our samples from a tall tower - is that these samples that we observe at the tall tower actually reflect what's going on for many hundreds of kilometres upwind.  On this particular day, we have a strong westerly wind.  So the sample that we're measuring right now will have come probably from Ireland, several hours ago.

Richard -   Let's have a look outside because you're on this hill top.  You can see the Tay bridge and Dundee.  Over behind us is a transformer buzzing away.  This heather - we look west.  I mean, you can't see much beyond this hill, but the wind is coming that way and I suppose it's coming from Northern Ireland, the Irish Sea, Western Isles, Glasgow, and then a vast track of countryside, and it's hitting here, and that's what you're measuring.

John -   Well that's right.  We're probably sensing air that's coming from Ireland, possibly from the Atlantic.  Indeed there are some days, you can actually measure the carbon monoxide that's come on forest fires in Canada.  It can come that far and our instruments are that sensitive that we can actually sniff the air coming from different continents altogether.

Richard -   And what are you finding?  You're presumably seeing a natural process, and you're also seeing our contribution, the human contribution to greenhouse gases.

John -   Well we are.  Particularly, we're looking at methane and carbon monoxide to look at the anthropogenic influence.  Carbon dioxide is a very interesting gas of course because it reflects what the natural vegetation is doing.  So we see a trend in CO₂ over the 5 years that we've been here, but we also see cycles in that trend as well, and that reflects what the biosphere is doing, what the oceans are doing, what the land surface is doing.  Also sometimes, if you're looking at carbon monoxide or methane, you see spikes or sudden increases.  They may all be because the air which is coming past our tower has actually gone perhaps Dundee or Glasgow or somewhere else then.

Richard -   Can you give an example then of something you've seen that you could say, well that's a result of a particular activity?

John -   Particularly on a calm clear night, perhaps you'd have a southerly wind at this site, and what we'd actually do is we would sniff Dundee, and we'd see that as a relatively high peak in our data.  As the day went on, as more mixing came along, that would go away and we'd start to see the natural influence.

Richard -   And that is the point really, isn't it?  You're measuring what's happening now, but you're looking at the trends and seeing what is happening to the atmosphere over time.

John -   I suppose what drives this science really is, where are the carbon sources and things?  We really don't know where carbon goes once it leaves your tail pipe or your chimney.  We know about half of it stays in the atmosphere and about half of it goes in the oceans, and the land.  So it's a bit like a detective story.  We can actually interrogate our data and figure out what the land surface or what the ocean is doing.

Dave -   That was John Moncrieff from the University of Edinburgh talking to Richard Hollingham. 
If you enjoyed that, there are more of Richard's podcasts as well as links to other Planet Earth resources here.