When it
comes to climate change research, most studies bear bad news regarding the
looming, very real threat of a warming planet and the resulting devastation
that it will bring upon the Earth. But a new study, out Thursday in the journal
Science, offers a sliver of hope for the world: A group of researchers based in
Switzerland, Italy, and France found that expanding forests, which sequester
carbon dioxide from the atmosphere, could seriously make up for humans’ toxic
carbon emissions.
In 2018, the
United Nations’ Intergovernmental Panel on Climate Change, the world’s foremost
authority on climate, estimated that we’d need to plant 1 billion hectares of
forest by 2050 to keep the globe from warming a full 1.5 degrees Celsiusover
pre-industrial levels. (One hectare is about twice the size of a football
field.) Not only is that “undoubtedly achievable,” according to the study’s
authors, but global tree restoration is “our most effective climate change
solution to date.”
In fact,
there’s space on the planet for an extra 900 million hectares of canopy cover,
the researchers found, which translates to storage for a whopping 205 gigatons
of carbon. To put that in perspective, humans emit about 10 gigatons of carbon
from burning fossil fuels every year, according to Richard Houghton, a senior
scientist at the Woods Hole Research Center, who was not involved with the
study. And overall, there are now about 850 gigatons of carbon in the
atmosphere; a tree-planting effort on that scale could, in theory, cut carbon
by about 25 percent, according to the authors.
In addition
to that, Houghton says, trees are relatively cheap carbon consumers. As he put
it, “There are technologies people are working on to take carbon dioxide out of
the air. And trees do it — for nothing.”
To make this
bold prediction, the researchers identified what tree cover looks like in
nearly 80,000 half-hectare plots in existing forests. They then used that data
to map how much canopy cover would be possible in other regions — excluding
urban or agricultural land — depending on the area’s topography, climate,
precipitation levels, and other environmental variables. The result revealed
where trees might grow outside of existing forests.
“We know a
single tree can capture a lot of carbon. What we don’t know is how many trees
the planet can support,” says Jean-François Bastin, an ecologist and postdoc at
ETH-Zürich, a university in Zürich, Switzerland, and the study’s lead author,
adding, “This gives us an idea.”
They found
that all that tree-planting potential isn’t spaced evenly across the globe. Six
countries, in fact, hold more than half of the world’s area for potential tree
restoration (in this order): Russia, the United States, Canada, Australia,
Brazil, and China. The United States alone has room for more than 100 million
hectares of additional tree cover — greater than the size of Texas.
The study,
however, has its limitations. For one, a global tree-planting effort is
somewhat impractical. As the authors write, “it remains unclear what proportion
of this land is public or privately owned, and so we cannot identify how much
land is truly available for restoration.” Rob Jackson, who chairs the Earth
System Science Department and Global Carbon Project at Stanford University and
was not involved with the study, agrees that forest management plays an
important role in the fight against climate change, but says the paper’s
finding that humans could reduce atmospheric carbon by 25 percent by planting
trees seemed “unrealistic,” and wondered what kinds of trees would be most
effective or how forest restoration may disrupt agriculture.
“Forests and
soils are the cheapest and fastest way to remove carbon from the atmosphere —
lots of really good opportunities there,” he said. “I get uneasy when we start
talking about managing billions of extra acres of land, with one goal in mind:
to store carbon.” Bastin, though, says the study is “about respecting the
natural ecosystem,” and not simply planting “100 percent tree cover.” He also
clarified that planting trees alone cannot fix climate change. The problem is
“related to the way we are living on the planet,” he says.
Caveats
aside, Houghton sees the study as a useful exercise in what’s possible. “[The
study] is setting the limits,” says Houghton. “It’s not telling us at all how
to implement it. That what our leaders have to think about.”
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