Thinking land cover change beyond carbon: estimating biophysical effects from satellite observations
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| License | CC Attribution 3.0 Germany: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal purpose as long as the work is attributed to the author in the manner specified by the author or licensor. | |
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Local GroupComputer animation
Transcript: English(auto-generated)
00:11
So, yes, I'm Gregory Duvalier, I work for the Max Planck Institute of Biogeochemistry in Jena, and I am part of the Open Earth Monitor project, and within that project
00:25
we're doing different research activities. Some of them have started, some of them have not. This one I'm going to talk about has not really fully started, but it builds upon some research that I've been doing in the past with other collaborators, among others.
00:42
And so my intention here is a bit to present what was done in the past to set the scene of what we will be doing in Open Earth Monitor, and yeah, so hopefully that's of interest for everyone here. And so the topic is about land cover change, but it's about land cover change thinking
01:02
a bit beyond what is typically done for many about just the influence on carbon. It's about thinking about biophysical effects of land cover change and how we can measure it from satellite and what we can do with it. But then there's carbon.
01:21
Many people know about this graph showing how much more fossil fuels emissions are increasing and how much on the other side we have an intake by, among others, the land. The land, the terrestrial land, is perhaps responsible for about a third of what is
01:41
emitted increasingly here in green, and one of the particular things about the land is that it's one of the most uncertain parts of the carbon budget. It changes a lot, so it's important. And land cover change comes in, well, also in the part as emissions. Many things due to deforestation are causing CO2 to add in the atmosphere, and it's the
02:06
yellow part. So land cover change and the land and the terrestrial land is quite an important part of the climate system. Now one of the solutions that is being shown a lot is about planting more trees to solve
02:21
this climate crisis, and of course this sounds like a good idea in many cases, and there's many pros. Of course, trees can help to sequester carbon, of course, and that you can also support biodiversity potentially, improve the air quality, and we'll get a bit into
02:43
this after, can also help to buffer against weather extremes. There's good reasons to plant more trees. However, there's also many challenges, and partly that might make it that this is not such a simple solution, of course. Well, trees take a long time to grow, so if you plant new trees before they have
03:03
an effect, they will take some time. It's not an immediate thing. Then the choice of species is very important, and there's many things that make it that maybe we should not plant just blindly any type of trees across areas that should not have them. Let's say the thing is more tricky, then by planting trees we're actually increasing
03:24
fire rates potentially, so this might be also something that will really make more carbon go to the atmosphere, and of course we have land use conflicts, because when you use land for planting trees, it's land we cannot use for something else. Bottom line is that for sure one thing to say up front is planting trees is not
03:43
a solution to reduce fossil fuel emissions. It can help to reduce some emissions that we will not be able to completely decarbonize in society, but most of the effort needs to be from stopping fossil fuel emissions.
04:01
However, the point is here that I wanted to talk a bit beyond carbon, because trees and ecosystems in general have an effect on the carbon cycle, but they also have an effect on hydrology and the surface energy fluxes. These compartments are a bit not so much talked about in the general climate community
04:24
when we do the pledges for the Paris agreements and things like that. Basically, if you think about the land cover, about the forest, it isn't changing, it's reflecting more light, it's actually evaporating water, and it's transmitting heat.
04:41
These are all things that are different, whether you're looking at a forest or a grassland. And so basically the green arrow is part of this biogeochemical part of carbon and the role it has when we change the land cover, but then this biogeophysical part has other effects, and they're not considered in general by IPCC yet or just partly mentioned,
05:07
but it's not part of all the pledges. And when you see the land cover changes that we are witnessing, we can change the surface of the earth quite a lot, and it has an effect on how much light is reflected back
05:20
into the atmosphere, for instance, based on the surface that we have and what we do with it. In extreme cases, like this is the coast of Spain, the plastic coast, sometimes it's like a place where we put so many greenhouses that the whiteness of the place actually makes
05:41
it that it's cooler than what we, that it actually blocks a bit the effect of climate change over there locally because it's so white, but this kind of things cannot be a sustainable solution everywhere, of course. However, there's other ways that we can do land cover change, and one thing that I wanted to raise a bit is like cover crops, for instance, in many parts of Europe, we
06:04
lease crops bare between the seasons, but then in some cases we can plant other crops like here in between these rows of maize, of harvested maize, there's still grass that can stay long and protect the soil. We did a study back a while ago when I was at the Joint Research Center with some colleagues
06:26
in which we tried to see how much more cover crops would, how would Europe look with more cover crops based on areas like that? How much does that be though? So how much of the, how much energy is reflected back if the soil is snow free?
06:42
And how much change could happen if we, if we had added cover crops? And actually it can actually make it that there is much less, much more energy reflected back when we do that. That was the result of the study that if we compared with carbon over the long run,
07:03
we could see some places where there could be an improvement, that in places here where you see points in yellow is basically where the part of this biophysics is more important than the carbon capture in short. And then we even thought, what about brighter crops?
07:21
And actually, if you think this would be the thing, if you put a cover crop that is with a normal chlorophyll, full of chlorophyll crop, but if you have some crops that are much wider like this, this is a chlorophyll deficient mutant. So a crop that actually has much less chlorophyll, then it has less chlorophyll to the point that it's much brighter.
07:42
And if you do that, you actually make the importance of how much is reflected shown by the yellow dots here is much higher. But I want to talk a bit more about the land cover, how we measure this from space and what we can do from space. We have many satellites measuring many different things, many different biophysical variables
08:04
that can be used to describe the surface. One of them that I've been focusing a lot is land surface temperature. So it's the temperature of the surface, the skin temperature that can be measured by satellite. And it has been shown in places like when we have heat waves,
08:20
like this image from the European Space Agency for a heat wave in Canada a couple of years back. So it's not the air temperature. It's the temperature, the radiometric temperature of the surface. But it's quite an indication of anomalies. These numbers can be much higher than air temperature because that's how it is physically.
08:40
But still, they're proportional to air temperature. And actually, for some reason, for some aspects, it is much more important to know the surface temperature because this is what is actually affecting the climate also radiatively above. And the technique that we developed back some time ago to apply this,
09:01
to see how land cover change could be used, to see the effect of land cover change on land surface temperature was trying to look in places like this, a contrasted zone where we have like tropical forest and a deforested savanna. And we assume that the forest, no, first, we have the forest that evaporates more.
09:25
And so this evaporative fraction actually makes it that this forest will cool more than the grassland. However, the grassland is brighter and typically a brighter body will reflect more and so might be cooler because it's brighter. Now, which one of these effects dominates?
09:44
That's a bit the question, no? Because this can vary depending on where you are in the world. And so the idea was that, for instance, in this tropical case, typically we would expect that the forest would be cooler than the grassland nearby.
10:02
The idea is that with the satellite, we can have one pixel looking here and one pixel looking there and comparing it. And if the comparison is done correctly, we can actually infer how much that forest, if it's deforested into that grassland, how much of a delta change in temperature could be expected?
10:20
And so it's a bit of a space for time methodology, basically. I'm not going to go into the details, but basically we have maps of forest cover on top, a fraction of land cover and the map of land surface temperature on the left. And by combining them together, we make a regression that actually allows us to map locally
10:42
based on the local moving window, how much we would expect a change from going from A to B, from a full cover of forest to a completely deforested cover. How much would we get based on the local contrast we have over there? And we might make a map out of that. We basically did a study in which we could do this kind of things across the world to see,
11:05
okay, locally, if we deforest here, how much are we changing the surface temperature? And we also could see what are the biophysical effect behind, if it's a question of albedo, if it's a question of sensible heat or latent heat that is behind.
11:21
But I let the details for that, for whoever is interested, you can contact me or read the paper. Here, the point is that we managed to see different land cover transitions and see if we change a forest type, for instance, we would have some value. If we do a deforestation in tropics, we would have another value of that value.
11:41
We actually made a quick back of the envelope calculation more or less to see from the deforestation, from what the vegetation changed from 2000 to 2015, how much would this have affected locally the temperature on top of any carbon-based
12:03
change in atmospheric temperature? And we came up to this number of local warming of 0.23 degrees, which is something on top of greenhouse gas effect. So this is a bit just to have an idea that, yeah, locally, this has a change, but there's other issues also that affect the climate system or the land atmosphere
12:24
interactions when we change land cover. One of them is about indirect effects. Here you see forest with clouds on top. Now, if you remember this figure I showed you, imagine we plant the forest. There is also one thing here that I didn't talk before is that on top of these,
12:41
you have the little clouds. And typically, we know that it's more susceptible to have more clouds above the forest than the grassland. How much can land cover actually do that and locally affect the cloud cover? That's an interesting question that partly we want to explore. And we know that there's several effects that actually change because of the forest,
13:03
like the surface, the roughness of the forest can actually lift the atmospheric boundary height for the details and actually create low-level convection and cumulus clouds. These cumulus clouds, I mean, there's many types of clouds. Here, we're talking just about these low clouds.
13:21
Actually, having high clouds typically warm the system of the world, but the low clouds cool it down because they're whiter and reflect more light. And actually, the ones I'm talking about are typically low clouds. So typically, one could imagine that if forests are making more clouds, it could actually cool down the earth to a point by this effect on top.
13:42
But we're very far from the research to know if this is so. But what we did do was with the same kind of thing that I told you about the temperature from a satellite looking at land cover and cloud records and seeing potential afforestation, what if we change crops or low-level grasses to trees.
14:03
And across Europe, we managed to see that depending on what type of trees we could plant, we would see more or less change in cloud cover, typically with higher cloud cover than not. Now, coming to the work planned in this open earth monitor project,
14:21
basically, we have a specific task there to try to develop some tool that can help at the EU to identify land-based mitigation potential. Basically, the idea is that this space for time methodology that I told you about, we're capitalizing on some work that we've had before in which we managed to
14:43
try to streamline the methodology in some open package in Julia language. But this is still in progress. And this will serve for a specific use case in the project to try to estimate local surface temperature changes following forest cover change in Europe in a more specific way.
15:05
I'll come into the detail with that. And we have a main stakeholder for this use case, which is precisely the Joint Research Center of the European Commission, which, because they have now an observatory for forest degradation,
15:21
forest deforestation and degradation. Basically, you might have seen this recently come up. So the EU observatory has been launched. And basically, this observatory would be able to have different layers of information. And our scope is to add this kind of thing, which is not so much talked about in general.
15:46
And actually, the GRC place has a big cloud computing platform, which we were asked also to interact with them. So that the idea is that the scope that we develop would be open access and open source,
16:00
then that could be ported to this platform so that they could run things to feed the forest observatory. So in a nutshell, the use case would work with refined forest land cover maps for EU, which probably we would be using some that our colleagues in the project will be
16:22
generating of identifying dominant forest tree species for Europe. And we want to use now sub-daily land surface temperature information from meteorological satellites. So basically, these satellites can measure at every 15 minutes,
16:43
the temperature of the surface when there is no cloud. And so because we think that, OK, we've been looking at things about the temperature. I didn't mention the details. We looked at just the temperature at a given point in time, which is just afternoon. But actually, the curve, the timing along the day might be much more interesting.
17:04
And this is what we were trying to explore partly. So we're going to be putting the work we've done already within the cloud computing system of the GRC. And based on these two different types of sources of data, we would be able to do some kind of potential maps of sub-daily surface temperature
17:25
for planned forest station. So the idea would be to have maps that say that, OK, if we put this type of tree here, would this be better or not for this temperature change of the surface? And talking with our stakeholder in GRC,
17:40
we actually identified that maybe we could explore also other things in Africa. Because actually, part of the EU observatory, the idea is also to see globally not just what's happening in forest types in Europe, but also what's happening elsewhere. Because all of commodities, think of cacao, coffee,
18:01
and other things that are driven by the consumption in Europe, well, we would want to see if these things might have a change in the local conditions where this has grown. So we're considering actually also to expand things maybe in West Africa. That's it from my side.