10
BBC SCIENCE
CLIMATE CHANGE
POST PRODUCTION SCRIPT
BBC SCIENCE
CLIMATE CHANGE
POST PRODUCTION SCRIPT
PART 1 OF 410:00:07 / Woman / This is the story of climate change.
10:00:12 / Man / But told in a way you’ve never heard before.
10:00:19 / Man / Because we’re not climate scientists, we’re three mathematicians
Man / And we’re gonna use the clarity of numbers to cut through the complexity and controversy that surrounds climate change.
10:00:37 / Woman / Understanding what’s happening to the Earth’s climate is perhaps the biggest scientific endeavour this human race has ever taken on.
Man / From the masses of data we’ve chosen just three numbers that hold the key to understanding climate change.
Woman / 0.85 degrees
10:00:59 / Man / 95%
10:01:02 / Man / And one trillion tons.
10:01:06 / Woman / Just by looking at these crucial numbers we’re gonna try and get to the heart of the climate change controversy.
10:00:24 / Woman / They are three numbers that represent what we know about the past, present and future of Earth’s climate.
10:01:18 / Woman / And it’s not just the numbers themselves that are important, the stories behind them, how they are calculated, are equally intriguing and revealing.
10:00:28 / Comm / We’ll see how the methods using everything from the Moon landings
10:00:30 / Woman / To early twentieth century cotton mills and motor racing have fed into the numbers we’ve chosen.
10:00:32 / Comm / These three numbers tell an extraordinary story about our climate and take us to the limits of what it is possible for science to know.
10:02:05 / Opening titles / CLIMATE CHANGE
BY NUMBERS
10:02:14
10:02:16 / Man
VO / MUSIC IN
Every minute of every day all over the planet scientists are collecting data on the climate. Around ten thousand weather stations monitor conditions of the Earth’s surface. Some twelve hundred buoys and four thousand ships record the temperature of the oceans. And more than a dozen satellites continuously observe the Earth’s oceans and atmosphere.
10:02:50 / Man
VO / All science starts with collecting data and when it comes to our climate we’ve got masses of it, but what story about our planet is all that data telling us?
10:03:03
10:03:11 / Woman
VO / MUSIC IN
Thousands of scientists are trying to answer that question, their results are summarised in a series of huge reports by the Intergovernmental Panel on Climate Change. The three numbers we’ve chosen all come from the IPCC’s reports.
10:03:37 / Woman / Molly.
10:03:39 / Hannah / I’m Doctor Hannah Fry and I use numbers to reveal patterns in data. I’m looking at one number that answers a critical question, is climate change really happening?
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10:03:58 / Hannah
PTC / Our first number is
Dr Hannah Fry
University College London
0.85 degrees. Now this number represents what we know about our climate in the recent past because it’s the number of degrees Celsius that scientists say our Earth has warmed since the 1880s.
10:04:20 / Hannah / But how can they be so precise?
After all our climate is complex and extremely varied. Temperatures change from season to season, place to place and even minute by minute.
10:04:42
10:04:55 / PTC / As if it wasn’t hard enough to try and find an average temperature of the Earth for now we also need to go back in time and compare it to the average temperature of the Earth in the past when we didn’t have the luxury of modern measurement techniques.
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10:04:59
10:05:42 / VO / Working out how the planet’s temperature has changed over more than a century is a huge challenge. It’s a bit like trying to work out the route I’m taking across this park, if you only had the route Molly is taking to go on. You have to identify the trend, my path, from all those changing temperatures, Molly’s path and it all starts with the quality of the data. Now that’s not such a problem for the recent past, but what about further back in time?
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10:05:45
10:05:53 / VO / MUSIC IN
Up until the middle of the nineteenth century the temperature record as measured by instruments is patchy and unreliable and there is some controversy about how you reconstruct temperatures before this time. But the record improves from the 1880s due to the efforts of one man.
10:06:27 / PTC / Now the key man in this story, the man with a plan, is a guy called Matthew Fontaine Maury. Now Maury was a lieutenant in the US Navy and from even when he was a small boy was obsessed with mathematics and data and analysis. But in 1839 Maury had a coaching accident where he broke his thigh bone and dislocated his kneecap and while he was recovering he spent his time studying captains’ log books. And the data that he found there set the path for his next fourteen years’ worth of work, so much so that on the 23rd of August in 1853 he called together a meeting of twelve countries surrounding the North Atlantic, all to talk about one thing.
10:07:08
10:07:11 / VO / MUSIC IN
He wanted to improve the way that data about the oceans was collected.
10:07:19 / PTC / Captains record all sorts of information in their log books, things like wind speed and direction, or the speed and temperature of the sea currents. Now this wasn’t just interesting to Maury from a scientific perspective, but also because it was something he could sell to commercial ship owners.
10:07:38
10:08:10
10:08:11 / VO
PTC / He found great commercial success from mapping the position of major sea currents like the Gulf stream which enabled ships to use the currents to travel faster. But there was a problem; different sailors took the same measurements in different ways. That was particularly true for one of the measurements climate scientists are interested in, sea surface temperature.
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Now the way to measure sea surface temperature is actually surprisingly simple, all you do is chuck a bucket over the side of the ship and get the temperature from it. But the problem is that the result that you get actually depends quite a lot on the type of bucket that you use, so let me just take the temperature of this now and in the meantime I’m gonna throw this guy over.
10:08:46 / VO / In the early nineteenth century some sailors used wooden buckets, others used buckets made of canvas. This meant that the measurements were not consistent.
10:09:01 / PTC / The wooden bucket’s coming out as a surprisingly warm, er 15.1 and if we make a comparison the canvas bucket, unlike the wooden bucket, isn’t insulated so things like, um the air temperature are gonna make a much bigger difference so the temperature has dropped below 15.1 degrees.
10:09:20 / VO / It may not sound like a lot but even tiny discrepancies undermine the accuracy of the data.
10:09:27 / PTC / Now Maury knew this and so at his conference in 1853 he came up with a standardised way for everyone across the world to measure sea surface temperature.
10:09:37
10:09:42 / VO / MUSIC IN
He wanted everyone to use wooden buckets and designed special forms for them to fill in with all their data. Maury also introduced standardisation to air temperature measurements on land. That’s why our 0.85 degrees Celsius figure is measured from 1880, it’s the date from which the temperature data is generally well standardised. But despite Maury’s efforts the data was still far from perfect, not everyone stuck to the rules, for example over time canvas buckets made a comeback because they were lighter, so there were still errors, some of which were pretty obvious.
10:10:2410:10:29
10:10:55
10:11:19 / PTC / So here is the sea surface temperature data between
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1880 and 1980. And the first thing that you really notice about this graph is this huge spike that happens where it looks like the sea surface temperature’s raised by 0.8 degrees Celsius. Or at least it looks that way until you realise that this spike happened, er in 1941 when during the Second World War understandably sailors didn’t much wanna go up on deck with a torch and a bucket to record sea surface temperature levels. So instead during that time they used, er the water that was coming in through the engine room which is hence why the data is a lot higher. Now after the Second World War people gradually started returning to using uninsulated canvas buckets, but unfortunately we don’t know who was using them or when. And so in all of this big mess of data how do we get accurate
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temperature readings for land and sea from the past?
10:11:27 / VO / The answer is related to a mathematical technique that was used to help solve one of history’s greatest challenges.
10:11:41 / VO / In a mission fraught with difficulties one of the biggest was how to navigate a quarter of a million miles through Space to the surface of the Moon.
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10:11:53
10:11:57 / VO / MUSIC IN
It’s a feat of navigation all the more astonishing when you consider how difficult finding our way around can be
even down here on the ground.
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10:12:07 / PTC / Working out exactly where you are on the Earth at any point in time is actually a surprisingly difficult problem, especially if you want really, really precise information.
10:12:18 / VO / It’s tricky because tracking opposition, just like measuring temperatures over time, is prone to error.
10:12:26 / PTC / Not the easiest thing ever.
10:12:28 / VO / Take dead reckoning, timing how long you’ve travelled in a particular direction from your last known position.
10:12:35 / Man / About three miles an hour.
10:12:36 / PTC / Lovely, three miles an hour, hang on one second.
10:12:43 / VO / It’s easy to drift off course as inaccuracies build up.
10:12:48 / PTC / Hang on.
10:12:50 / VO / Even more high tech methods can get it wrong.
10:12:54 / PTC / Actually the GPS is putting us over there at the moment which is less than ideal.
10:12:59
10:13:06 / VO / So when it comes to navigating the problem is which measurement of your position do you trust?
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In the 1950s a young Hungarian born mathematician, Rudolf Kálmán, devised an elegant algorithm to solve this problem.
10:13:17 / PTC / Kálmán’s method uses a matrix algebra, er and takes into account all of the errors to give you the best possible estimate of your position at any point in time.
10:13:30 / VO
Video clips / So how does Kálmán’s method work? In 1969 NASA gave it its ultimate test in the mission to land men on the Moon. Navigating in Space poses particular challenges. The spacecraft was being tracked by four radar stations on Earth. Onboard instruments were also estimating its position, but each of these measurements could be wrong. So how could NASA be sure of Apollo Eleven’s position? This is where Kálmán’s algorithm came in. Moment by moment it compared each position measurement with the others, looking for differences that fell outside the expected margin. If the algorithm had found significant disagreement the mission would have been aborted, but it didn’t and the rest is history.
10:14:59 / PTC / So this process is now known as Kálmán filtering and has been used in everything from, er cleaning up
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grainy video to looking for trends in economics. And a lot of the underlying principles are exactly the same as you see in the processes used for climate science. So, er knowing when to trust your data and picking out when the errors are big enough to flag up a deeper underlying issue, but the process in climate science is
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instead known as homogenisation.
10:15:33 / VO
Video clips / Homogenisation has allowed climate scientists today to clean up data gathered in the past. Unreliable measurements can be corrected or discarded.
10:15:47 / PTC / So what homogenisation process is doing effectively is taking all of the data from all of the weather stations and comparing it on a day by day basis. Now in doing that if a particular data set starts to look a bit unusual it will really stand out.
10:16:05 / VO / You can see what happens when scientists homogenise a data set by looking at how they corrected the unusual jump in sea surface temperature in the early 1940s.
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10:16:17
10:16:29 / PTC / So once you’ve applied this homogenisation process here is what the sea surface temperature data will look like. So we have the original data here, er in yellow and the cleaned up version
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also available in blue.
Now the first thing that you notice is that the big jump that we had in 1940 has dramatically reduced, er there is still a bit of a jump because there was an El Niño that year which meant that the sea surface did actually warm. But the jump that was down to the difference in measurements, the, the error in the way that people were measuring, has been taken away completely from the graph.
10:17:00 / VO / All the big scientific groups that work with climate data use homogenisation methods like this to try and clean up the records of past temperature.
10:17:12
10:17:27 / PTC / And it’s absolutely vital that you account for some of these errors in measurement that have occurred in historical data otherwise you’ve got no hope of finding any kind of underlying patterns in your data. But inevitably as soon as you start applying these mathematical
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recipes to clean things up other people will start accusing you of building in biases into your data.
10:17:37
10:17:52 / VO / Perhaps the best defence against bias is scientists’ own scepticism. Many different groups work on climate data using slightly different homogenisation methods and all are subjected to searching scrutiny
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by their peers. But even after homogenising the historical data climate scientists face a further problem, gaps in the temperature record. Even today we do not have temperature measurements for the whole planet.