Why the Amazon doesn’t really produce 20% of the world’s oxygen

Why the Amazon doesn’t really produce 20% of the world’s oxygen.

As the news of fires raging in the Amazon spread across the world last week, so did a misleading yet oft-repeated claim about the rainforest’s importance: that it produces 20 percent of the world’s oxygen.

That claim appears in news coverage from CNN, ABC News, Sky News, and others, and in social media posts by politicians and celebrities, such as French president Emmanuel Macron, U.S. Senator and presidential candidate Kamala Harris, and actor and environmentalist Leonardo di Caprio.

Some have taken it to mean that we’re at risk of jeopardizing the world’s oxygen supply. “We need O2 to survive!” former astronaut Scott Kelly tweeted last week.

However, the figure—which has earned the forest the title “lungs of the Earth”—is a gross overestimate. As several scientists have pointed out in recent days, the Amazon’s net contribution to the oxygen we breathe likely hovers around zero.

“There are a number of reasons why you would want to keep the Amazon in place, oxygen just isn’t any one of them,” remarks Earth systems scientist Michael Coe, who directs the Amazon program at the Woods Hole Research Center in Massachusetts.

Cradle of biodiversity

Nevertheless, the 20 percent myth has been making the rounds for decades, though it’s unclear where it originated. Malhi and Coe reckon it stems from the fact that the Amazon contributes around 20 percent of the oxygen produced by photosynthesis on land—which may have erroneously slipped into public knowledge as “20 percent of the oxygen in the atmosphere.”

Obviously, none of this is to say that the Amazon isn’t important. In its pristine state, it makes a significant contribution to pulling carbon dioxide out of the atmosphere. Coe likens it not to a pair of lungs, but to a giant air conditioner that cools the planet—one of our most powerful in mitigating climate change, alongside other tropical forests in central Africa and Asia—some of which are also currently burning.

The Amazon also plays an important role in stabilizing rainfall cycles in South America, and is a crucial home for indigenous peoples as well as countless animal and plant species.

“Very few people talk about biodiversity, but the Amazon is the most biodiverse ecosystem on land, and climate change and deforestation are putting that richness at risk,” notes climate scientist Carlos Nobre with the University of São Paulo's Institute for Advanced Studies.

For its importance to the world, the Amazon might as well be a metaphorical pair of lungs, and this analogy may have been helpful in galvanizing action around deforestation. But to most researchers, it doesn’t make much sense—not least because actual lungs inhale oxygen rather than exhaling it.

“If people want to relate it to a fundamental part of their body that maintains stability and maintains life, maintains wellbeing—symbolically, you can make some kind of association,” says Nobre. “But physically speaking, it’s not really the lungs of the world, no.”