 My name is Corinne Lechiri. I work at the Tindall Center for Climate Change Research at the University of East Anglia. And I work on the carbon-climate interactions. I first studied in high school physics, I really liked. I had a very good teacher and then I decided to do physics at university. But then I couldn't really find very much to do with physics. And I thought meteorology was a very interesting application of physics. I loved the weather. I just could see outside all the applications. So I registered to a master's in meteorology and I just drifted into climate science from there because they're really similar. The weather is climate science over very short periods and climate science is how the weather changes over decades. I focus now on carbon cycles. So I became interested in the drivers of climate change. So why is the climate changing? And carbon emissions is the biggest factor. So carbon is increasing in the atmosphere. But it doesn't entirely stay there. So about half of the emission, maybe even a bit more than half of the emission that we put in the atmosphere, end up in the natural environment. It ends up in the ocean and in the forest. And I'm very interested to look at what processes. So why does the carbon change pool? Why does it go from the atmosphere to the ocean? And is this limited? Is this going to continue forever in the future? Or will there come a point where the sinks will saturate or stop and stop absorbing this carbon we're putting in the atmosphere? There are mainly two carbon reservoirs that absorb carbon. We call them carbon sinks. The one that I'm most familiar with is the ocean carbon sink. So the ocean is potentially a huge sink for carbon. Say if we wait to the few thousand years, maybe 70% of the CO2 that we put in the atmosphere would end up in the ocean. But this happens very slowly because the interface between the atmosphere and the ocean is the ocean surface. It's very small compared to the whole ocean that is underneath the surface that we don't see. It's very deep and it has a very big mass and it can store a lot of carbon. So what happens is the carbon comes from the surface and it dissolves. It penetrates in the ocean, but then it has to be transported from the surface to the deep ocean where its real potential for storage is in the deep ocean where there's so much water. So I'm looking at these processes, so what determines how much carbon goes in the water this year, how much will go next year, and so on. And that depends on what is in the atmosphere and how fast the ocean circulation turns around. We have a lot of measurements, millions of measurements in the ocean surface of how the CO2 is changing. And the first thing that we see is that the CO2 is increasing the same way that CO2 is increasing in the atmosphere, but there is evidence that the CO2 in the ocean may not be following or may not be increasing at the same rate as the atmosphere. So the carbon sink, maybe we say weakening, so maybe not be so efficient at absorbing emissions as it used to be. And there's a lot of uncertainty in this because we don't quite have sufficient large-scale observation to know particularly whether that's a global problem or not. But I've worked a lot on the Southern Ocean, and the nice thing about the Southern Ocean is that it's almost all water. You have no continents south of maybe 30 south, so there's a whole chunk of the planet that is mainly ocean. So what you can do there that you cannot do elsewhere is look at the change in the carbon sink from the atmosphere. So you only measure in the atmosphere, you don't measure in the ocean, you measure in the atmosphere and you see what's happening underneath. And you can't do that in the Northern Hemisphere because there's too much exchanges with the forest and that blurs your signal. But we did this in the Southern Ocean, we used observations from others in the atmosphere and we looked at the 20-year period, was the carbon sink increasing as fast as we expected? And it wasn't, it was slowing down compared to the expectations. And we were able to link this at the time with the increasing wind at the surface of the ocean that is caused in part by climate change and in part by the depleting ozone hole, which is another human-induced problem. So we see changes there, they're only 20 years long, so it's not quite long enough to see whether these change are really persistent through time. But it's long enough to actually really be quite concerned and look quite a bit more carefully about how the sinks are behaving. So the oceans are warming and the carbon doesn't dissolve so much in warm water as in cold water. And so that is a factor that reduces also the effectiveness or the efficiency of the carbon sink in the ocean. But that's a well-known factor, so we account for this all the time when we do climate projection, we account for the well-known factors and that would be one of them. And the other one would be simply the chemistry of the carbon as it penetrates in the ocean. But the less well-known factor is how the ocean's circulations will change and how the marine ecosystem will change potentially affecting the carbon cycle. This is really where the source of all of the cutting-edge research, let's say, is. There's another very important carbon sink and that's the terrestrial biosphere and the processes there are completely different whereas in the ocean it's passive, so it's circulation, chemistry, the biology hasn't got very much to do in the ocean with the carbon sink just a little bit. And the terrestrial biosphere is completely different, it's plants. So forest trees grow more under more CO2 and their roots also build more so that when the trees and the leaves degrade, they accumulate in the soil and they pile up. And so it's a completely biological process on land. So in the natural carbon cycle there's a lot of fluxes of carbon dioxide. So carbon goes in and out of the ocean, in and out of the terrestrial biosphere every year. I mean in the terrestrial biosphere and the trees and the forest it's very easy to see if you live in a place that has a forest area with seasons, you see in the winter the trees they have no leaves and the spring comes and the leaves build up. This is all good carbon dioxide that goes in the leaves and in the fall, in the autumn when the leaves fall down then the carbon is emitted back in the atmosphere. So you have a huge signal there of CO2 going in and out of the atmosphere. What we're doing now is putting everything out of balance. So we're adding carbon to the atmosphere. It's new carbon, it's not part of the natural cycle. It's one that we've dug out of the fossil reservoir where they were stored and we've put them back in the atmosphere. This is new carbon and it puts the system out of balance. So the ocean and the terrestrial biosphere they're not at equilibrium with the atmospheric concentration of carbon that we have now. They're in disequilibrium and that's why we have carbon sinks and carbon uptakes of human emissions because we are not in equilibrium. The natural sink absorb about 55% of the CO2 emissions year after year so more than half of the emissions go in the natural environment. It's a huge service to humanity that the carbon sinks do. We keep track of fossil fuel emissions through energy statistics. So all countries around the world they report how much fuel they burn so coal or gas and this is quite well accounted for because it has a lot of economic implications. For instance, countries tax the energy system so companies that produce energy they have to declare how much they have burned and so these statistics are available and you can then transform the energy that is used through two CO2 emissions by looking at what they have actually burned and what is the quality of say the coal that has been burned. So this is how we account for the emissions. This is accounted for at the country level and then you can sum them up and account also for bunker fuels so fuels for shipping and fuel for aviation that come on top. Emissions from land use are accounted traditionally also by a statistics process. So countries declare their changes in land patterns so if they have a change in forest but also if they change from a crop land to a pasture for instance they have to account for that and they declare this to the FAO, the Food and Agricultural Organization and they published statistics on land cover areas so what is the cover change. Land use CO2 emissions are much more difficult to account for than fossil fuel burning and that's because when you burn fossil fuel you put the CO2 straight away into the atmosphere so it's instantaneous. If you cut a forest it's quite different. What happens is you cut the forest, you harvest the timber, the timber goes into furniture then typically the farmers will burn the residuals there's a little fire in their emissions there and also you have a secondary source which comes from the soil decay which takes some years to decades so you have a pulse to start with and then you have decades of decay to account for so it's much more difficult to account for the carbon emissions in that area. However, even with all the uncertainties together the CO2 carbon dioxide emissions from the forest sector is less than 10% of the total carbon emissions because the fossil fuel burning is so dominant. The main sources of uncertainty are for what is the quality of the fuel that is burned and how much of the fuel is burned so if you burn coal do you burn all the way to the bottom or do you burn is there some residual so these are the main uncertainty. Another big source of uncertainty is uncertainty that comes from countries in transition so if you have say a growth of emissions of 10% per year because you're in a very rapid stage of development then it's really difficult to keep track of statistics like energy that vary so fast. Once the transition is finished then the statistics become much easier to handle so this is another large source of uncertainty. This is much more difficult to account for so we try to account it's a small part the methane leaks in the carbon budget so usually we live with the uncertainty that we have what is a bigger topic at the moment is the methane leak in the methane budget so this methane concentration are starting to increase in the atmosphere after having been stable for 10 years and part of this is thought to be caused by increasing methane emissions but the source has not been determined yet. We know that there's emissions from fossil fuel that are unaccounted for and we know also that there's a contribution from wetlands tropical wetlands mostly so at the moment we don't have evidence for large emissions from permafrost so this is a big topic of research at the moment. Volcanic emissions of CO2 are very small there are about 1% of the emissions that we have now so it's a tiny fraction themselves they are negligible what they do however is when you have a volcano you change the climate a little bit for a year or two and then you have a response of the carbon sinks so the terrestrial biosphere for instance has more growth in the years that follow a volcano and so you can see a pulse in atmospheric CO2 because of the volcanic eruption a pulse, a sink in atmospheric CO2 actually not even a source but the source that comes from volcanoes directly is very small we don't monitor CO2 emissions from volcanoes directly but other teams around the world monitor atmospheric concentration of CO2 very accurately and then you can, if there was a big signal from volcanoes you would see it in the atmospheric CO2 network very clearly so what happens when we put carbon emissions into the atmosphere new carbon from burning fossil fuel or from deforestation what happens is it takes a long time for this carbon to readjust in the land and ocean eventually if we're prepared to wait long enough so that's thousands of years a lot of this carbon maybe 70% will end up in the ocean and the reason this takes time is that you have different adjustment times so the CO2 goes in the surface ocean it takes about one year to dissolve but how it is transported from the ocean surface to the intermediate and to the deep ocean depends on the ocean circulation and the ocean circulation takes hundreds to a thousand years to mix the entire ocean so that's the time scale that is really relevant here is take a molecule of CO2 we've put it in the atmosphere how long is it going to come before it ends in the deep ocean and it's a long period there's not one single time frame because there are several different reservoirs so there's a reservoir you could say the surface ocean is a reservoir because it sees the atmosphere every year with the season and the deep ocean is another reservoir and then on land again you have different reservoirs you have the biosphere that is above the ground and then you have the upper soil and then you have the deeper soil so we have to wait until all of these reservoirs have responded to the perturbation and that's why it takes about a hundred years for carbon dioxide to actually re-equilibrate what we call airborne fraction is the amount of the carbon emissions that we put in the atmosphere from human activity so the fraction of that stays there here I put one emission so one unit of carbon dioxide typically the airborne fraction will be 0.45 so 45% of the emission this year will remain in the atmosphere climate science is a very interesting problem from a scientific perspective it has very strong foundations so physical-based foundation we understand the mechanisms we understand the processes there are uncertainties of course but the uncertainties we know what they are and where they are there are in quantities if we put more carbon dioxide in the ocean in the atmosphere, apologies if we put more carbon dioxide in the atmosphere we will get more warming so this is all scientifically based this is where the science can assist society in making decisions that are good for itself I think that's what its role is climate scientists could be more proactive in explaining their science and talking about their results to the public in general to schools, to events, museums, policy makers and so on they could talk more they could make it more clear what their science is all about what our science is all about I think that would be really useful I think that also scientists could make a little bit more of an effort to simplify or to explain a little bit more simply what the consequences of their results are what their results are simply not just the consequences I think we have a lot to learn in terms of making sure that the results that we find that have implications for society are understood