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Fires are still burning across the world's largest rain forest. Some studies show they could trigger what scientists call a death spiral that could turn the Amazon into a dry savanna. What would that mean for Earth's oxygen levels? Science writer Peter Brannan wrote about this for The Atlantic magazine, and he talked with our co-host David Greene.
DAVID GREENE, BYLINE: A lot of people were tossing around this concept that the Amazon really is the lungs of the planet. You seem to suggest that is just not the case.
PETER BRANNEN: Well, yeah. So deforestation in the Amazon is something we should all be worried about. It's a huge carbon sink. It's got just immeasurable biodiversity, and there's indigenous tribes there crowded out by ranchers and people who are burning down their home. And so there's all these reasons to be concerned about the Amazon. And there is a little bit of confusion, though, about this, whether it provides the planet with its oxygen, or there's this number thrown around, 20%. Or maybe it's 6%.
GREENE: I've seen that a lot, yeah, 20% of the world's oxygen supply comes from the Amazon. Is that not the case?
BRANNEN: Yeah. I mean, that's a little confused from sort of a bigger picture of where our oxygen comes from. You know, it's encouraging that it is not a major threat if we, you know, burn every forest down in the world. Obviously, we don't want to do that.
BRANNEN: But the reason is actually kind of unsettling, as well. And it has to do with the formation of fossil fuels, of all things, is why we ended up with the amount of oxygen we have in the air. And the fact that we're digging up and burning fossil fuels is actually dropping oxygen faster than, you know, burning down the forest on the surface of the planet.
GREENE: Digging up fossil fuels is more dangerous, potentially, to our oxygen supply than forest burning?
BRANNEN: Luckily, we have so much oxygen in the atmosphere that we basically couldn't make a dent in it at all.
BRANNEN: Now, the reason for this is that when a plant dies, or a bloom of plankton dies, if it somehow gets buried and that oxygen never gets used up, over geological time, you can build up a reservoir of oxygen in the air like we have today. So we really have all of Earth history to thank for every breath we take.
GREENE: Can I just ask you about one thing our listeners heard? We had a reporter from the region in Brazil, and I was asking him about this 20% number and he said if you destroy more rain forest, it starts to dry out and it absorbs less carbon dioxide, and that could be a real bad situation for climate change. Is that accurate?
BRANNEN: That's a huge problem, and it's something to be incredibly concerned about. So far, I think, 17% of the Amazon has been deforested by humanity, essentially. And there might be a threshold around 20 to 25%. This was reported by James Temple in the MIT Technology Review, that if you get to that point, there might be this feedback loop where it starts drying out, and then it no longer becomes a carbon sink like it is today, but it eventually could put up lots of carbon dioxide into the air and virtually make meeting the Paris climate agreement goals impossible. Like, this is one of the many reasons we should be very concerned about the rain forest.
GREENE: It's not just fires in the Amazon. We're seeing this in different spots around the world - Alaska, Indonesia, Siberia. I mean, what does this tell us in terms of the battle against climate change?
BRANNEN: I mean, it's predicted by, you know, every model that we're going to have more drought. There's going to be more wildfires around the world. The really strange thing, which I write about in my story, is that not only are we burning down trees on the surface of the planet but we're essentially, as a species, trying to dig up all the forests ever in Earth history. So this is things like coal, and oil, and natural gas. So we're trying to dig up all of the life, ever, and we could burn down way more organic carbon and burn through way more ancient life underneath the earth than exists on the surface of the planet. So we're really doing something very strange on this planet and running a weird experiment that's never been run before.
GREENE: Science journalist Peter Brannen. Thanks so much. We really appreciate it.
BRANNEN: Thank you. I appreciate it. Transcript provided by NPR, Copyright NPR.