Scientific proof that reforestation is the top climate change solution

The Crowther Lab's latest research proves that reforestation is the top climate change solution – by far. This episode, which features Prof. Dr. Thomas Crowther and Dr. Jean-François Bastin, explores this ground-breaking discovery and what it means for the future of our planet:

Here's a transcript of our conversation:


Joshi Gottlieb: The Crowther Lab has changed how I see trees. This group of scientists has uncovered new ways of mitigating climate change by restoring plants and soils across the globe. In this episode, I speak to Tom Crowther –

Tom Crowther: I’m a global ecosystem ecologist –

Joshi Gottlieb: And Jean-François Bastin –

Jean-François Bastin: I’m a specialist in remote sensing and forest ecology.

Joshi Gottlieb: They both work at the Crowther Lab, and in this episode of the Ecosia Podcast, they tell me about their latest discovery.

Tom, you’ve already quantitatively shown that trees are among our most effective strategies for climate change mitigation. And in your latest paper you try to find out how many trees the land could potentially support. And you do that by creating a map.

Tom Crowther: That’s exactly right. We’ve generated the first global map of where trees can naturally exist under today’s climate. And that helps us to understand how many trees can go there, and how much carbon they can store.

Joshi Gottlieb: In that paper you say that, and I quote, "we then used a random forest machine learning approach to examine the dominant environmental drivers of tree cover and generate a predictive model that enables us to interpolate potential tree cover across terrestrial ecosystems." My question is: what on earth does that mean?

Tom Crowther: Essentially, in summary that means we just take loads and loads of data from people collecting it all around the world, and by describing what environments they're in, we can use machine learning to predict how many trees exist in every type of environment in the world. And then, when we extrapolate across the globe, we get a global map of where trees can exist.

Joshi Gottlieb: Right, and thanks to this technique you found that, excluding agricultural and urban areas, there is room for an additional 0.9 billion hectares for continuous tree cover which could store 517 billion trees and 205 gigatonnes of carbon. What do these numbers mean? What would it mean to remove this much carbon from the atmosphere?

Tom Crowther: Well that’s exactly right, the nice thing about this is that it provides the first quantitative understanding of what we can really do to offset climate change. If you think, since the start of the industrial revolution, humans have been omitting loads of carbon in the atmosphere and about 300 gigatonnes of it is still in the atmosphere. And very simply put, this new model shows that in the areas that are available for restoration, where forests would naturally exist, we can capture two thirds of that carbon just in the above ground part of those trees. And if you consider then that there's loads more carbon that would go into the roots, and in the soil, this really places restoration as - by far - the best climate change solution proposed to date.

Joshi Gottlieb: And how does reforestation compare to what is usually presented as the top climate change solutions?

Tom Crowther: There’s a company called "Project Drawdown" that lists the top climate change solutions, and they list "effective refrigeration management" as the very top climate change solution. It could prevent the future emissions of 89 gigatonnes of carbon. If we all stopped eating meat tomorrow, we’d save 66 gigatonnes for future carbon emissions. And those are the top solutions, and there're hundreds that go down. Now restoration has always been placed really far towards the bottom because we’ve never had that quantitative information. But it's only now that we can say that restoration is not only extremely important but it is far, far more powerful than the next best climate change solution.

Jean-François Bastin: On top of that I would like to add that it is also a very cost efficient solution in the sense that it doesn’t cost a lot to plant a tree. It doesn't require advanced technologies in order to do it. So it’s a very easy way to fight climate change.

Joshi Gottlieb: So in that case we should really get started. Where is the land where all these trees could be planted? Are there any countries that stand out?

Jean-François Bastin: When you look at the map of the potential areas for restoration you can see that this potential is really distributed everywhere around the globe, in all the biomes. But when you start to look at countries you can find about 50% of the potential for restoration in only 6 countries. What was interesting for us is that those 6 countries are mainly developed or about to be developed countries. Those are the USA, Canada, China, Brazil, Australia and Russia. In those 6 countries you can store about 100 gigatonnes of carbon, which is enormous.

Joshi Gottlieb: Just thinking about all you’ve said, I’m kind of surprised that global reforestation and restoration is not more talked about. It seems there's much more talk of things like plastic pollution, say. Do you think that the discussion will start to include restoration and do you hope that your research will help with that?

Tom Crowther: That is the perfect question. Really, forest restoration has always been seen as a nice ‘happy clappy’ climate change solution and people around the world go, "aw, it would be nice to plant a few trees but really what contribution does it have?". And that is for the very simple reason that we have never had a quantitative, scientifically relevant global understanding of what the restoration potential is. And so we’ve never been able to place it next amongst all of the other climate change solutions. Now that we have this global, quantitative understanding, not only can we say that restoration is until now the best available strategy that we have for capturing massive scale carbon, but it’s also the most economically viable. There's projects out there restoring trees for 30 cents a tree, that means restoring the one trillion trees around the world that we need would cost only $300 billion – that’s a snip for some of the world’s richest people. It’s really something that doesn’t require immense scientific or technological advancements, which most of  the other climate change solutions do, and it also doesn't necessitate top-down decisions from governments. If your government doesn’t believe it, you can still get involved in restoration projects to offset climate change and to improve biodiversity and all the other ecosystem services that come with it.

Joshi Gottlieb: Have you drawn any other practical conclusions from you research? Not just this paper but your research in general.

Tom Crowther: I think from a scientific perspective we’re realizing that it’s absolutely necessary to take a holistic perspective. If you're talking about carbon storage above ground, you must absolutely understand the consequences for carbon storage below ground if you are going to really understand how we’re going to manage ecosystems quite right. But I think the nicest take home message that we can get from this is that we have here, in global restoration, a climate change solution that everyone can get involved with. You know for the last few months, 1.5 million people have been marching about their frustration about climate change. But none of them have known how to actually get engaged because we just rely on scientists or governments to do the job. Now we have a solution where anyone can get involved, either by restoring ecosystems themselves or providing funding for restoration projects like Ecosia that support restoration all around the world. Or simply by investing wisely when you invest in companies. All of these strategies can be really valuable in our efforts to live more sustainably and to support ecosystems across the globe.

Joshi Gottlieb: That must be one of the most inspiring messages to come out of scientific papers! Thank you both very much.

Jean-François Bastin: Thank you.

Tom Crowther: Thank you so much; it was great to talk.



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