Hey, smart people, Joe here.

Fact: earth is experiencing climate change at a scale and pace never before seen since our species has been on the planet, and we're causing it by pumping more heat-trapping carbon into the atmosphere than earth's natural systems can take out.

Now fixing a problem as massive as climate change is going to take a ton of different solutions, but more and more people are asking if trees might be a big part of the answer.

For the past 370 million years or so, they've been one of the major ways earth sucks excess carbon out of the atmosphere and stores it away.

And along with green plants and algae, this natural technology captures carbon better and cheaper than any human technology we've come up with so far.

But can trees actually make a big enough difference in cleaning up our mess?

Or are we-- well, barking up the wrong tree?

I'm going to dig into three different ways that trees might help solve climate change: planting a bunch more trees; saving the trees we've already got; and whether the field of synthetic biology might give scientists the power to hack photosynthesis and make trees even better at being trees.

[THEME MUSIC PLAYING] If you were paying attention to YouTube last year, then you probably heard about Team Trees, a project created by MrBeast with help from Mark Rober to raise $20 million to plant 20 million trees by... well, now-- 2020.

And they succeeded-- or really, all of us did.

We basically took over YouTube with tree videos, and to date, Team Trees has raised over $21 million to plant 21 million trees, which is insanely awesome.

But the Team Trees team made one thing very clear-- The 20 million trees by 2020 isn't going to cure climate change, but it's a step in the right direction.

So, like, what does 21 million trees do for the climate?

Tom from the channel Aspect Science made a great video analyzing how Team Trees works that you should check out for more details.

But long story short, 21 million trees covers an area a lot less than you'd think.

And according to researchers, an area of new forest that size can capture 4 million tons of carbon dioxide spread out over tens of years.

Considering that the world emitted more than 40 billion tons of carbon dioxide in 2019, we would have to do Team Trees literally thousands of times to plant enough trees to suck it all up.

Sounds pretty impossible, doesn't it?

Well, it might not be.

Meet Felix Finkbeiner.

Today we want to convince the world to plant a trillion trees.

That's roughly the number of trees we have space for, globally.

[JOE] The seed for this idea began when Felix was in just fourth grade.

During a presentation I was giving about climate change back then, I had to tell my classmates that we should plant 1 million trees in each country of the world.

My classmates loved the idea.

They were super enthusiastic about planting trees.

A few weeks later, we planted our first tree without really knowing where we would go from there.

Two local journalists reported about this first tree.

That's how some other schools found out about it.

And that's when a real competition kicked off-- who would plant the most trees?

And that's how Plants for the Planet spread.

[JOE] A few years after that class project, Felix's group planted its millionth tree and he was invited to tell his story before the United Nations.

But for us children, forests are our future.

[JOE] There he met someone very special.

By far, the most important person in this story was a woman called Wangari Maathai from Kenya.

There are some people who have changed the world in incredible ways that almost everyone knows about-- Gutenberg and the printing press; Albert Einstein and relativity; Jonas Salk and the polio vaccine.

But there are others that, for some reason, we never learn about.

Wangari Maathai is one of those people.

Maathai was an African biologist who had an idea.

[FELIX] But one of the most beautiful things she did was she essentially used tree planting as not only a tool for nature conservation, but also for women's empowerment.

When I was nine years old, I heard about this fantastic work, but I didn't understand the true depth of it.

I only understood that tree planting helps tackle the climate crisis and saves the polar bears.

[JOE] She won the Nobel Peace Prize for her work, but few people know her name.

So what impact would planting 1 trillion trees have?

We used to have roughly 6 trillion trees on earth.

So this was before humans starting cutting them down.

And now we have about half of that remaining.

So we've got 3 trillion instead of 6 trillion trees.

Ideally, we want to go back to the 6 trillion, right?

Get back every tree we lost.

But of course we need space for our settlements, and much more for agriculture.

But we can get about another 1 trillion back.

They wouldn't solve the climate crisis on their own, of course.

We also need to drastically reduce our global CO2 footprint.

But they make it possible to ensure that the global temperature does not rise by more than two degrees.

And if we manage to plant these trees, they would capture about a quarter of human-made CO2 emissions.

Remember, trees are basically big carbon-storage machines that suck CO2 out of the atmosphere and turn it into more tree.

Cutting those trees down and either burning them or letting them decompose just puts that carbon back in the atmosphere.

Most deforestation happens in earth's tropical regions.

If this tropical deforestation were a country, it would be the third biggest emitter of carbon in the world after China and the U.S.

Almost one-third of all the world's carbon emissions since 1850 have come from deforestation.

These days, forests remove about a quarter of the CO2 humans emit into the atmosphere each year and store it away.

There is more carbon locked up in the world's trees than in all the fossil fuels still remaining in the ground.

And beyond carbon, tropical forests act sort of like the planet's air conditioning.

They pull moisture out of the ground, release water vapor into the sky, and literally create rain and weather patterns across the globe.

Cutting down these tropical forests can raise nearby temperatures by as much as 3 degrees Celsius.

So the point is, keeping the trees we have is essential if we want to keep climate change from getting even worse.

To put this challenge into scale, if Team Trees gave us 21 million trees, the 2019 Amazon wildfires that took over social media burned at least 1 billion trees.

And this year's Australian bushfires may have burned more than 10 billion trees.

Luckily, protecting the trees we already have is cheaper and easier than planting new ones.

But natural processes, like photosynthesis, on land and in the ocean, are only absorbing about half the CO2 that we currently emit every year.

If you think of it like money, we're spending more than we earn in our carbon budget.

And many experts think saving trees and planting as many new ones as we can are both part of the answer.

There is one more idea that can make a big difference, and it relies on something called synthetic biology.

When plants like trees take carbon dioxide out of the air, they use a tiny molecular machine inside their cells called an enzyme to grab CO2, stick that carbon onto another molecule, and eventually make sugar.

This molecular machine's name is a mouthful: ribulose-1,5-bisphosphate carboxylase oxygenase.

But you can just call it RuBisCO for short.

Just about everything on earth that does photosynthesis-- algae, cyanobacteria, grass, trees, you name it-- uses RuBisCO to grab carbon out of the air.

Scientists think it's the most abundant enzyme on earth.

This little molecular machine has completely reshaped our planet.

The problem is, RuBisCO isn't very good at its job.

Many molecular enzyme machines can carry out thousands of chemical reactions in a single second.

RuBisCO is super slow.

It can only grab five to ten CO2s every second.

And about one out of every five times, RuBisCO grabs the wrong molecule-- oxygen instead of CO2.

It just wastes energy in the process.

If we could make this biological chemistry work better and faster, maybe we could pull even more carbon out of the atmosphere.

Some scientists have put genes for RuBisCO inside bacteria in an effort to rapidly evolve a more efficient enzyme.

By manipulating the genetic sequence in the DNA code for the enzyme, researchers can make many, many more versions of RuBisCO than nature can on its own.

And perhaps one will be faster and more efficient at grabbing carbon out of the sky.

Other researchers are digging through the enormous toolbox of chemical reactions that exists in nature to look for totally new ways to capture carbon.

These researchers start by designing a highly efficient chemical reaction on paper, then plugging in individual molecular machines from different species in order to build the chemical process from scratch.

These are pathways that don't exist in nature built almost like Legos by combining different molecular machines that do exist.

But even if scientists do figure out a way to improve on biological chemistry, we can't instantly go upgrade every photosynthetic organism on earth, including trees.

But it might give us a new way of capturing carbon using biological reactors in places where emissions are high or even linked to devices capable of artificial photosynthesis that can work alongside the trees and plants we already have.

Unfortunately, it will take decades of research to engineer these molecular machines to be even close to what nature can already do today using low-tech, carbon-sucking, light-eating machines like trees.

Trees are a solution we already have.

But as I hope you've realized by now, even if we saved every tree that already exists, and even if we planted trees in every spot on earth that could hold them, we still wouldn't be absorbing all the climate-changing carbon that we emit each year.

The bottom line is this: no matter what climate-change solution we're talking about, whether it's trees or electric cars or next-generation nuclear reactors or synthetic meat, none of it will work unless we stop putting so many greenhouse gases into the atmosphere.

It's really that simple.

Solving climate change isn't just about what we do, it's about what we stop doing too.

Stay curious.