The headlines about a study published earlier this week were alarming.
“Tropical forests losing their ability to absorb carbon, study finds,” blared The Guardian. “The Congo rainforest is losing ability to absorb carbon dioxide. That’s bad for climate change,” The Washington Post warned.
But it would be a mistake to write off tropical forests as no longer our allies in the fight to halt climate change.
As it turns out, the paper, titled “Asynchronous carbon sink saturation in African and Amazonian tropical forests” and published in the journal Nature, presented some good news and some bad news.
Let’s start with the study.
The study looks at mature forests. What it finds is that mature trees in Africa and in the Amazon are still absorbing climate-warming carbon dioxide from the atmosphere. That’s the good news. Trees don’t just absorb carbon dioxide when they’re young and growing, they are still absorbing when they’re older — mostly because there’s extra carbon that humans have put in the atmosphere, which acts almost like fertilizer. So they’re absorbing carbon, which is a good thing — but it’s for a not good reason.
The bad news has to do with what the researchers found when they looked at how that carbon absorption is changing over time. In Amazonia, it has been slowing down for a few decades (though is still positive). In Africa, the study found evidence that it is beginning to slow down.
So the mature forests are still absorbing carbon — a miracle, if you think about it — but they have been absorbing less each decade, which is not good.
The other bad news is why these forests are absorbing less CO2 than they used to. The study’s authors found the biggest reason is that mature trees are dying more often, even as they are growing faster due to CO2 fertilization. And this is because the habitats they live in have become hotter and drier — likely driven by climate change itself.
So that’s the bad news — that decades from now, mature forests may reach a point where they are no longer absorbing any carbon overall.
To understand the significance of tropical forests for addressing climate change, what the study does not say is also important.
This study does not find that mature forests overall are emitting carbon — that is, sending more carbon back into the atmosphere than they take in. That would be, to put it bluntly, very bad. The study doesn’t even find that they will be net emitters of carbon in the next several decades. In that sense, carbon absorption by mature tropical forests is, more aptly put, a good thing that is becoming less of a good thing.
This study for the most part also focuses on mature forests only. It is not new research on the rates that humanity is clearing forests. That these trees will be less good at absorbing carbon in the future (from an estimated 2.5 gigatons of CO2 per year in the 2010s to 1.1 gigatons per year in the 2030s), probably due to climate change, is a reminder that we cannot just assume nature will solve our problems while we continue to ratchet up our emissions and our impact on nature.
Unfortunately, we continue to clear tropical forests at an alarming rate. That is where excess greenhouse gases from tropical forests primarily come from — to the tune of 4 gigatons or more of CO2 a year.
In terms of the big picture — how humanity can avoid climate catastrophe — the observation that mature tropical forests are becoming less good at absorbing our excess carbon than they used to is a bad thing. But the implication in some media accounts is that it is a terrible thing, that forests overall are going from friend to foe, and that it’s all out of our control.
The reality is that protecting forests — keeping them from being destroyed — and restoring them would have a much greater impact on climate-warming emissions than the changes that scientists are observing in this carbon absorption slowdown.
And the reality is that the fate of tropical forests is not yet out of our control. In fact, protecting and restoring forests (alongside shifting to a low-carbon economy) are the most important things we can do to slow and stop climate change. These are solutions we can implement right now and are available in countries around the world.
If we can do that in time, we will lessen climate change itself, which may reduce the warming and drying the study finds is slowing down carbon absorption. So tropical forests are among our best allies—still—in cleaning up humanity’s carbon problem. But we have to act now.
Will Turner is the senior vice president of global strategies at Conservation International. Want to read more stories like this? Sign up for email updates here. Donate to Conservation International here.
Cover image: The cloud forest on top of Chyulu Hills, Kenya (© Charlie Shoemaker)