Professor Joanna Haigh, Imperial College London: What climate change is

Tim Hughes: But now it's time for our first panel. This panel is going to focus on an introduction to climate change. So we're going to hear from four speakers. So the first speaker we'll going to hear from is Joanna Haigh from Imperial College London. And she'll be talking to us about what climate change is. Then we'll hear from Professor Ed Hawkins from the University of Reading, and he'll be talking about the impacts of climate change. Thirdly we'll hear from Professor Rebecca Willis, who is one of our expert leads from the University of Lancaster. She'll be talking about why tackling climate change has proved a difficult issue in the past. And finally we'll hear from Chris Stark, also one of our expert leads from the Committee on Climate Change. He'll be talking a bit more about what we as an Assembly are going to cover. So, as I said, the speakers will speak - they'll each speak for about 10 minutes - and they you'll have an opportunity to at your tables note down those questions. So without any further ado I'm going to hand over to our first speaker, so Professor Joanna Haigh.

Joanna Haigh: Well thank you very much - it's a real honour to be here and I hope I'll be able to introduce climate change in a way that is accessible to you all. I should have a talk somewhere (indecipherable). A ha, introduction to climate change.

So first of all, what is climate? We all know what weather is, you know, it's sunny, it's windy, it's hot or cold. And we can measure those things - we can measure the rainfall. And climate is essentially the average weather for a particular place. So you might say that the average maximum temperature in Birmingham in January is 7 degrees celcius. And that would be the climate of Birmingham. But the weather from day to day might of course be warmer or colder than that. So the highest temperature ever measured in Birmingham in January is 15 degrees. So another important part of climate is how often do we get these extreme temperatures? So the average temperature is 7, but how often does it go above 12, say? So all those statistics will be collated and then we understand what the climate of Birmingham, or the West Midlands, is. And climate change is just when there's a long term shift in those conditions. So we have long term measurements, measurements over years and decades of those parameters and we see whether or not the average temperature and the extremes have changed.

So how do we know that? Well there's measurements of all these climate parameters in a number of different ways. Since about the 1970s there's been satellites. So satellites go round and round the world all the time taking these measurements, and they're provided of course for the weather forecasters. So the Met Office will get these data all the time. But the climate people can collate all these data, collect them and analyse them. And we've now got forty or fifty odd years of satellite data telling us what the temperature has been doing over the world. But going back further than that, there of course weren't satellites, the instrumental period - so thermometers could be used from about the 1850s, and they've been at various weather stations over the globe. And again, the data is collected and analysed. And that's a very careful subject that needs to be done, taking into account all sorts of factors about different thermometers in different places and whether the air has changed in terms of urbanisation and that sort of thing. So very carefully collected data over the world. Going back over longer periods, so over thousands of years we can tell what especially the temperature and the humidity has done from looking in indicators like in tree rings and in corals and in stalagmites and ocean sediments. They can tell us what the temperature and the humidity has done over these very much longer periods. And indeed if you want to go over hundreds of thousands of years, we can look at the air trapped in ice cores. They take cores from the ice in Antarctica and Greenland and measure the air trapped, and they can tell from that what the temperature and the humidity was at that time. So these are the sort of records that are used to find out what climate is and whether or not it has changed.

So these are the instrumental - the temperature measurements taken by thermometers over the last 170 odd years. You can see, it has different coloured curves there, and those different coloured curves are each analysed by different groups of scientists. So that's independent measurements, so you can see the slight differences between the colours, but they're generally saying the same thing. And then the grey shading is an estimate of what we think the range is. So, of course, measurements are not absolutely precise, so we need to know within what range we believe that to be true. And that's what the grey shading is telling us. So you can see that it starts off - it's sort of bobbling along, but it's fairly flat and then it starts about 1900 to go up, it flattens off, and then it starts going up again very sharply, so that nowadays the temperature is about - on a global average - one degree warmer than it was in the 1800s. And this is, of course, what's become known as global warming, and really it's the background to everything that we're here talking about today.

Now I need to go into a little bit of science - I hope this isn't going to put you off - but, to understand what is happening to the climate, we need to understand what is happening to what heats up and cools down the atmosphere. So all the energy that's driving the climate system, that's making the winds blow, that's making the temperatures, etc, is coming from the sun. There's a tiny, tiny bit of energy coming out of the centre of the Earth, but that's completely negligible compared with the energy coming from the sun. So if we look on a long term average – a global average, an annual average – and average everything else out, there’s a certain amount of heat coming in from the sun, and that has to be balanced – if there’s no climate change – with the same amount of energy going out. So what we’ve got is the solar energy coming in, and on the right there you’ve got some heat energy going out. And those have to be balanced. But what we find is that the energy coming in from the sun - about half of that gets to the surface of the earth and warms up the surface, and then that surface gets warm and it wants to put out heat – heat radiation. But the atmosphere is such – it’s composition is such – that only 10% of that escapes directly to space, and about 90% is absorbed in the atmosphere. So the atmosphere itself gets hot - it’s made of material, it gives out heat in all directions including downwards. So then the surface is getting more heat than it had done originally from just the sun. And the temperature rises until everything else is balanced out, such that the radiation going into space is equal to radiation coming in from the sun, but the surface is warmer than it would be otherwise due to the composition of the atmosphere. And this is what we call the greenhouse effect. It’s a perfectly natural thing. In fact it’s a rather good thing – it’s a lovely thing because without the greenhouse effect, the temperature of the earth would be about 30 degrees colder than it is. And so life couldn’t have developed in the way it has on the planet. So in absolute terms the greenhouse effect is something we like – thank you very much. And the main greenhouse gasses causing that to be the case are firstly water vapour – so the water vapour in the atmosphere, that’s a very very strong greenhouse gas. And the second one is carbon dioxide, and there are smaller ones which I’ll mention later, but those are the two most important ones. So if we change the chemical composition of the atmosphere, we can change the effect of this greenhouse, and the temperature of the earth.

So let’s have a look at what factors cause the climate to change. Which factors will influence this radiation balance – this equilibrium – that we’ve got the earth in? So there are of course natural factors, for example, if there is a big volcanic eruption, it can chuck a whole load of stuff up into the air, and the particles can stay there for about two years. And when that happens, it reflects sunshine to space and there are measurable changes – cooling of the earth’s surface – so we know that big volcanic eruptions cool the planet temporarily. Then if we have changes in the sun – if the sun was to give out more or less energy, clearly, that would cause the global temperature to go up or to go down. It also responds to changes in the earth’s orbit around the sun. So those are the natural factors. In terms of human factors, I’ve already mentioned greenhouse gasses. So if we add to the greenhouse gas composition of the atmosphere, that will cause the surface to warm. And other factors – so, I put industrial pollution. If we put a lot of particles up into the atmosphere from industrial processes, or perhaps agriculture or whatever, they can act like that volcano I mentioned earlier and can reflect radiation to space and cool the atmosphere down. And also changes in agricultural land use can affect the climate – Jesus, I’ve only got two minutes left, oh dear. So for example, if we cut down a lot of trees, they won’t be absorbing the greenhouse gasses that they were before. Or if we cut down a lot of trees and make the surface brighter, that will reflect sunshine to space.

Now, perhaps I will miss the bit at the bottom, but I can answer questions about it later. Sort of factors that add or reduce from the initial forcing factors.

So greenhouse gasses – I’ve mentioned carbon dioxide – and the human produced greenhouse gasses, about three quarters of them are carbon dioxide. We can’t add to the water vapour in the atmosphere, because as soon as - if we were to try and put more in, it would just rain out again – it’s sort of controlled. So there’s carbon dioxide coming from fossil fuels, mainly, and land use, and then the next most important ones are methane and nitrous oxide, which are largely associated with agricultural practices. So this is a measure from Hawaii – so that’s right out in the middle of the Pacific Ocean, so very clean air, it’s not coming from the local industry or anything – of the carbon dioxide concentration of the atmosphere. This is quite an incredible picture – and it’s showing that since 1960 the composition has gone, in these units, from 320 to over 400 units. So that’s very clear indication that carbon dioxide has been increasing. And if we go back even longer in time, that little red mark there is what I just showed you, but the rest of the picture is carbon dioxide concentration over the last 800,000 years. So you can see over the last 800,000 years the carbon dioxide has never been as high as it is today, and in fact it’s probably higher than it has been for 3 million years.

And I said that here. We know that the increase is mainly due to the combustion of fossil fuels, and there’s several reasons how we can deduce that, which I can answer questions about to anybody that wants to ask. Carbon dioxide remains in the atmosphere for about 200 years. It just goes up there and it stays there. There more we put up, the more that stays there. It’s going to accumulate, and these are the countries that are responsible for the accumulation. So, of course, when the industrial revolution started in the 1800s, if we’d looked at which country was most responsible, that would have been the UK, and we started everything off. We were responsible for kicking it all off. And the biggest country up there would have been the UK. But now if we look in 2018 who has been most responsible for the current state of emissions, the total that is in the atmosphere now, the biggest one is the USA and we’re down there at fifth. So we’re not a minor contributor even now.

And this is an important graph – it’s showing temperature – the black line there is the same temperature graph I showed you before: warming from 1880 to the present time. So that’s the black line. And the grey lines are calculations from computers. The big computers that are used to forecast weather can also calculate climate. There’s two sets of calculations there – the bottom set is only natural drivers, so we run the models with the factors, only the changes in the sun and the volcano that we know has taken place and we look and see what happens to the temperature. You can see it’s going along, there are some spikes due to volcanoes, and there’s a spread of uncertainty but it’s carrying along – it doesn’t have the global warming. And it’s only when we put in the human factors, which is the largely greenhouse gasses but the industrial processes and all the rest of it, that we can match the observations of temperature.

This is my final slide – she’s smiling! We know that the global temperature rise is due to the accumulation of greenhouse gasses. And it’s accumulating – the temperature is responding to the accumulated amount of CO2. So if we wanted the temperature rise to stop at a particular temperature level, we’ve got to stop the CO2 rising. That means we’ve got an absolute total amount of CO2 that we can put in the atmosphere before we go above that temperature. And that amount of CO2 is called the carbon budget. If we carry on going past what we know is the carbon budget for global warming of, say, 1.5 degrees, then something needs to be done to take the carbon dioxide back out of the atmosphere again. And I think – the bottom one – keep warming below 1.5 degrees means reducing emissions to net zero by 2050 – approximately. So we’ve got to slow down emissions and stop them to effectively zero by 2050. Sorry for going too long.

Tim Hughes: Thank you very much, Joanna. So I’m sure that's