To what extent can forests combat climate change? A sensor in space has answers.

Over the past century, governments around the world have drawn borders to protect thousands of the world’s most valuable ecosystems from destruction, from the forests of Borneo and the Amazon to the savannas of Africa.

These protected areas have provided lifelines to species threatened with extinction, supported the way of life of many traditional communities and secured water supplies for cities.

But the reserves are under increasing pressure, with their boundaries largely ignored as people cut down trees and encroach deeper into the ecosystems set aside for protection.

Now, high in orbit, a new way of looking at forests makes it clear that protected areas, even under attack, can still provide a crucial buffer against climate change. Scientists use laser technology to measure the biomass of forests around the world, allowing them to calculate how much planet-warming carbon the trees keep out of Earth’s atmosphere.

Quantifying the ability of protected ecosystems to store planet-warming carbon has long been a challenge for researchers. That’s largely because older, flat satellite images cannot distinguish how tall or wide trees were.

“We can use these new satellite data streams to monitor forest benefits in three dimensions and do the carbon part of this in a way that we could never do before,” said Laura Duncanson, a remote sensing scientist at the University of Maryland and a from the authors of A research based on the new data.

According to the study, protected areas around the world have helped combat deforestation over the past two decades and prevent a year’s worth of fossil fuel emissions from entering the atmosphere.

The study, published this year, showed that policies designed to protect nature can also be important for combating global warming, Dr. Duncanson said. She called the findings “a nice side benefit” of global forest conservation.

‘People want to grab what’s left’

The Tapajós Environmental Protection Area, a forest in the state of Pará, Brazil, which is larger than New Jersey, was created in 2006. It is intended as a ‘green wall’ to counter a wave of destruction in the Amazon rainforest that came with it. a newly paved highway known as BR-163, said Mauro Pires, the president of the Chico Mendes Institute, the government agency that oversees Brazil’s reserves.

Today, despite its protected status, the Tapajós is among the most severely affected areas in the Amazon. The rivers are polluted with chemicals from illegal gold mines and they are losing at least 3 percent of tree cover since it was established almost twenty years ago.

Keeping an eye on the region is a huge challenge, says Ronilson Vasconcelos, who heads a 17-member team responsible for monitoring a dozen protected areas, including the Tapajós.

“People are eager to take what’s left, like gold and wood,” he said. “It’s hard to let people let go of something that makes them so much money.”

But according to the recent study, the Tapajós is still one of the forests in the world that is most successful in avoiding CO2 emissions. Comparing the reserve to areas that were similar 20 years ago but never officially protected, researchers concluded that if the Tapajós had been wiped out, additional carbon equivalent to the amount produced by 900,000 Americans would have been released into the atmosphere each year.

“It’s very clear that it worked,” Mr. Pires said, but it’s not “magic work.”

While many countries have agreed to protect a greater share of the world’s ecosystems, political pressure to get rid of the reserves is growing, and keeping them safe is becoming increasingly difficult.

Protected areas, long thought to be protected by their remoteness, are increasingly threatened as countries expand their economies.

“Almost all protected areas are becoming much more accessible and much more vulnerable,” said Lisa Naughton, a researcher who studies protected areas at the University of Wisconsin-Madison. “Not just for local subsistence hunting and illegal timber extraction, but also for things like artisanal mining and road penetration.”

A ‘missing piece to our understanding’

For decades, scientists have sought more effective ways to calculate the amount of carbon stored in forests, grasslands and mangroves.

Then in 2018, NASA launched a mission called Global Ecosystem Dynamics Investigation (or GEDI, pronounced like the knighthood in “Star Wars”), deploying a sensor in space with the power to make accurate 3D measurements of vegetation. below.

“That was actually a very important missing piece in our understanding of the global carbon cycle,” said Ralph Dubayah, the mission’s principal investigator.

For the study published this year, researchers working with GEDI used the data to compare hundreds of thousands of protected areas around the world – including California redwoods, Indonesian mangroves and European forests – with a set of areas that were similar but unprotected in the year 2000 stayed.

They then calculated how much carbon in each of these ecosystems would have been lost to the atmosphere without protection.

Those calculations still require scientists to make assumptions, says Maurizio Santoro, a researcher at Gamma Remote Sensing, a Swiss company, who was not involved in the recent study. Calculating how much carbon a particular ecosystem contains requires knowledge of which species occur there, and in many cases that picture is incomplete.

Still, he said, GEDI allows scientists to do something that wasn’t possible before.

Reservations were most meaningful, the study found, where they blocked the wave of destruction around them, even if they weren’t perfect. (Some protected areas locked up huge amounts of carbon, but didn’t make much of a difference overall because the surrounding areas were not threatened.)

“This is not to say that protected areas are these pristine, pristine places where forest carbon is never lost,” said Dr. Duncanson. But, she added, “in places where there is a lot of deforestation, there is a good chance that those forests will be lost unless you have protection.”

Protected areas can slow decline by affecting the flow of investment, even if boundaries are not strongly enforced.

For example, many companies will not build a timber project in a legally questionable area. And public infrastructure, such as roads, is often diverted to unprotected areas. Ambitious farmers may choose not to deforest an area because they believe they will never gain clear ownership of the land.

“If you talk to the people who do hunting, charcoal production and woodworking, they know in a sense that somewhere, even if it is not clearly visible on the ground, there is a line that should not be crossed,” said Paolo Cerutti . the head of the activities of the Center for International Forestry Research in the Democratic Republic of Congo.

Experts say actively protecting reserves is crucial to keeping them intact. Efficient law enforcement teams are essential, Brazilian official Pires said. Without these reserves, they gradually lose their perceived value and governments come under increasing pressure to remove protection altogether. Furthermore, indigenous peoples and other traditional communities, who have been expelled from certain protected areas in the past, tend to be very effective at preserving trees.

The NASA program was halted in March but is expected to come back online early next year and provide more data until 2026, when the mission will be reassessed.

Researchers at the program hope that a long-term record of forest carbon data will help governments prove the value of protecting native ecosystems and attract more funding for protection. The fight to curb climate change may depend on their success.

Countries with large forests have the ability to reduce their emissions at a lower cost through conservation, Mr Pires said. But first, he said, they must “deploy these areas and provide them with the conditions to remain safe.”

Methodology

The before-and-after images of protected areas were created using historical images from Landsat, an Earth-observing satellite mission jointly managed by NASA and the US Geological Survey, and compiled using Google Earth Engine.

Each image reflects a multi-year average. Mosaics for the 1980s were created using images from Landsat 4 and 5 collected between 1984 and 1990. Mosaics for the present were created using images from Landsat 7, 8 and 9 collected between 2020 and 2023. To reflect the influence To reduce seasonal variations on vegetation, those date ranges were further narrowed. For example, the images used to create the Tanzania mosaic were limited to those collected between June and September each year. Clouds, cloud shadows and water pixels were also filtered out.

The boundaries of protected areas were downloaded in November 2023 from UNEP-WCMC and IUCN 2023, Protected Planet: The World Database on Protected Areas.