How Many Trees Would We Need to Plant to Slow Climate Change?

Trees pull and store carbon, but lots of land that could support them is deforested. Learn how researchers think planting trees could help mitigate climate change in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff. Production of I Heart Radio, Hey
brain Stuff Lauren vog obamb here. In recent years, climate
change has loomed like a dark specter over the globe,
contributing to everything from gentrification in Miami is high income
coastal dwellers seek new residents fur their inland away from flooding,
two refugees fleeing drought and crop shortages in Guatemala. But

(00:24):
the urgency around the issue reached new heights in the
United Nations. Intergovernmental Panel on Climate Change or IPCC stated
that rapid, quote, far reaching and unprecedented changes in all
aspects of society would be needed in order to drop
carbon dioxide levels by and prevent catastrophic global warming. Scientists

(00:45):
have indeed proposed drastic measures, just not the way that
you might think. In the same i p c C report,
the u N suggested that adding two point five billion
acres that's one billion hectares of forest to the world
could help limit global warming in future decades to just
two and seven degrees fahrenheit that's one point five degrees celsius,
which would stave off some of the worst effects of
climate change. And now the U N might just have

(01:08):
the data to back up their proposal. In another study
unveiled in July of twenty nineteen and the publication Science,
a group of researchers associated with the Crowther Lab in
Switzerland found that global tree restoration to the tune of
nine hundred million acres that's point nine billion hectares of
canopy cover, an area that's approximately the size of the
United States is quote our most effective climate change solution

(01:30):
to date. That would require upwards of half a trillion trees.
These trees would store two hundred and five billion tons
of carbon, or roughly two thirds of the carbon that's
been omitted by we humans since the Industrial Revolution. Some
news reports said that this much forest restoration is the
equivalent of roughly one trillion trees, but that statistick is
from an estimate in a report from but we spoke

(01:55):
with the current studies lead author Jean Frascois Bastin via email.
He said the idea was to estimate what tree cover
could be expected when you removed the human factor, i e.
What specific types of forest would naturally occur in the
absence of other development and where. The team used the
form of artificial intelligence known as machine learning to build

(02:16):
quote a model to link tree cover with climate, soil
and topography based on seventy eight thousand observations of tree
cover in protected areas. The researchers then projected the data
further to estimate the potential total tree cover of the
whole planet if human civilization didn't exist. But of course
humans do exist, so the team then excluded land currently

(02:39):
being used for urban settlements, crop lands, and existing forests,
which yielded the total amount of land available for restoration.
The study offers a map showing how much tree coverage
different parts of the globe might support, the top three
areas being Russia, Canada, and the United States. The studies
timing a lines of current global efforts around ecological rest ration.

(03:00):
A one example is the Trillion Trees Vision, which seeks
to restore one trillion trees by fifty Another is the
Bone Challenge, which is a partnership between the Government of
Germany and the u n's International Union for Conservation of
Nature that aims to restore three seventy one million acres
of deep forested land by which is about of the

(03:21):
current studies recommendation. You might be thinking, well, that sounds
pretty easy. Let's all roll up our sleeves and save
the planet by planting one tree at a time, right,
But some experts say the situation is actually a little
more complicated than that rosy picture, especially if most nations
don't chip into help. Although by fifty eight nations had

(03:42):
banded together to commit an acreage that would exceed the
BONB Challenge goal, most of the restoration work to date
has been done by only a few countries. We also
spoke with Jim Hallett, chair of the Board of Directors
for the Society of Ecological Restoration. He cited major challenges
to implementing restoration on such a global scale, quote including financing, governance,

(04:03):
land tenure and ownership, and capacity to do the work.
There's ample evidence that in some contexts, if the benefits
of restoration are not equally shared, the project will fail.
So incentive programs have to be carefully developed, and restorational
loan will likely not be enough. It takes time, after
all to implement such a big restoration projects, and also

(04:23):
for these trees to store carbon, and how it stresses
that we have to not just restore previously forested lands,
but preserve what we've currently got. Other scientists question not
only the practicality of the studies claims, but also the
studies very methodology. But we spoke with Ica Liling, climate
change researcher and professor of horticultural sciences at the University

(04:44):
of Bonne. He pointed out that some of the areas
marked for restoration couldn't support more trees than they already do.
Some of them are in permafrost regions for example. Also
quote the methodology implicitly, probably not on purpose, implies that
carbon stock is portional to canopy cover i e. Ecosystems
without trees contain no carbon. This is clearly false and

(05:06):
strongly inflates the global estimate of restoration. Young Barner, Leedling's
colleague and a professor for economics of sustainable land use
at the University of Bonne, is similarly skeptical. Barner says
that some of the areas being proposed for restoration under
the current study are already in use for other purposes.
Barner considers the study to be a quote interesting academic exercise,

(05:28):
but as a climate change mitigation strategy proposal, and it
is being advertised as such, it sends a misleading signal
to the international climate policy debate, but don't fret. Both
Bustine and Hallett emphasize that the u N has declared
thirty the Decade on Ecosystem restoration, which could spur nations
to act quickly, and some countries are already tackling the

(05:51):
initiative head on. And according to Hallett, forest restoration boasts
far more perks than just impacting climate change, including maintaining
or even increasing bio diversity and preserving the ecosystem that
we humans rely upon for our food and water. But
even the studies authors acknowledge that it's going to take
a lot of goodwill to make this grand vision of reality.

(06:13):
Bastine said, what we need is a universal action. International
agencies and geo's governments all citizens anyone can be involved.
Local communities and small organizations may be especially effective. While
they do not have the same reach as national agencies,
they have the benefit of knowing what works best in
their own backyards. Today's episode was written by Terry our

(06:38):
Lagata and produced by Tyler Clang. The brain Stuff is
a production of iHeart Radio's How Stuff Works. For more
in this and lots of other topics for everyone to
take part in visit our home planet, howstf works dot
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