- What happens when a scientific paper goes viral?

Well, a few years ago, YouTube sensation, MrBeast started getting hundreds of messages and comments asking him to plant trees.

So he set an obviously unattainable goal of planting 20 million trees, made a catchy video where he helped plant the first 2000, and against the odds seemed to have exceeded the goal.

He raised over $20 million to do it.

But was it worth it?

All of this happened because of a viral scientific study.

Most studies don't get much attention.

So when people all over the world took it as a call to action, you'd think it would be a huge success for the scientists behind it.

But according to NOVA's new documentary, it wasn't.

- It nearly finished all of our careers.

- That's confusing because right now the planet has around 3 trillion trees that collectively soak up about 25% of the carbon dioxide we've pumped into the atmosphere every year.

But over our history on earth, humans have chopped down about half of the world's forests.

That means we've lost around 3 trillion trees and with them half of the earth's most powerful carbon capturing system.

So when a team of ecologists, including Tom Crowther, figured out that Earth actually has the capacity to support a trillion more trees without disturbing our cities or farmlands, it quickly became a bipartisan call to action.

Because the thing is a trillion trees has a nice ring to it.

So in this episode, we're going to uncover what went wrong with the Trillion Tree campaign, and we're also going to check on the trees that MrBeast planted.

Did they survive?

Are they storing carbon?

We're about to find out.

So first, how did they plant over 20 million trees?

MrBeast and a lot of other YouTubers, including science communicator, Mark Rober teamed up to raise over 20 million dollars.

He made his own video about planting trees by drone in what looked like industrial timberland.

There are some real scientific problems with this approach to carbon storage, which we'll get to in a bit.

But he did have one of the best explanations of the relationship between CO2 and trees that I've ever seen.

- If you have a tree in a big pot, as the tree gets bigger, the soil level doesn't go down at all.

The mass comes from thin air.

- So over 50% of a tree is made up of actual carbon that's taken right out of the air in a process we call photosynthesis.

And it's put into a durable storage in every part of the tree, including the trunk.

So planting them should be good for the planet, right?

Well, it is, but this is where things get tricky.

- Everybody thought that meant planting trees.

Somehow it, it wasn't about the forest, it was about the trees, and that is where things started to go wrong.

- A few years ago, Tom went public about his experience on what went wrong with the viral Trillion Tree campaign.

Our friends over at NOVA made a whole episode about it.

So we decided to collab with them since MrBeast basically planted his trees in the Weathered production teams backyard.

But first, let's go back to a few years ago when I went into the forest with a friend of the show, Dr. Bev Law.

Our interaction really starts to shed light on why focusing on planting trees instead of focusing on the forest could be a problem.

She measures how much carbon is absorbed and released by forests in a network of stations all over the world.

You made this groundbreaking discovery, right?

So you put this carbon monitoring site in an older mature forest, and I see the same thing here in this younger forest.

So what have you found?

- Well, we found that this site was a source for about the first 20 years.

Right now it's about 22 years old.

- So a carbon source meaning.. - Net carbon source.

It's not taking up as much carbon from photosynthesis as is given off by respiration from the soil in the trees.

- So it's emitting more carbon - Yeah.

- than it's absorbing.

- Yeah.

People are being told or thought that young trees grow fast and vigorous, but when you look at the forest, the net of all the respiration and photosynthesis makes them a source.

- Here's the problem.

Timber companies in this region harvest their trees at around 45 years of age, which means forests used for wood products will spend very little time as a carbon sink.

The young trees will absorb carbon to grow, but according to Bev's research, it will be a net loss.

Here's Bev and another clear cut.

- Before this forest was cut, it looked like this one back here.

They were about 75, 80-year-old trees.

They did the clear cut.

You see all this slash here?

It's branches and stems that they didn't want.

So they leave it on site and about 50% of, of what is intended harvest ends up left on site and it decomposes.

- As all that decomposes the carbon it once stored is released back into the atmosphere.

This graph shows carbon storage in a forest that's cut down.

The line drops during the cut and stays flat for 20 years and then ticks back up.

Cut it again in 45 years and you can see the problem.

But a forest that's allowed to grow old has far more needles and leaves photosynthesizing, taking carbon out of the atmosphere and turning it into trees.

- Up around mature ages 80 and a hundred years old, they're really taking up a lot of carbon from the atmosphere and they've already stored 80 years of carbon.

- The biggest problem with a tree farm mindset may be this.

Taking carbon out of the atmosphere today is much more valuable than in 20 years.

That's because every fraction, a degree of global warming makes crossing irreversible tipping points more likely like thawing permafrost in the Arctic, coral bleaching, or Amazon rainforest dieback.

And with carbon dioxide at over 420 parts per million in the atmosphere, we really don't have time to misinterpret the science behind carbon storage if we hope to avoid the worst impacts of climate change.

But what about MrBeast and his 20 million dollar tree planting campaign?

Even though the saplings won't grow to reach net zero until 2040, did they even survive?

Our team looked all over the state park he visited, and finally in the backfield we found them.

Remember, MrBeast and his crew planted at least 2000 trees in this area, and sadly, this is all that was left, but let's count them.

Okay, so we have about 118 trees out of 2000.

If that's true, it's only a 6% survival rate.

But what went wrong?

Why did so many die?

Well, old forests are not only good at storing carbon, they're also good at staying alive.

During hot summers, their shade keeps the forest floor moist, while roots act like sponges.

This combination keeps temperatures cooler under the canopy, making the forest much more likely to survive an event like the 2021 heat dome, which pushed nearby temperatures up to a record breaking 124 degrees, which might've killed MrBeast's trees.

Still, forests are a crucial part in tackling climate change.

Today, about 48% of carbon emissions stay in the atmosphere and warm the planet.

26% are absorbed by oceans and 29% by vegetation and soil.

Any pathway towards net zero carbon emissions will involve reducing the amount of carbon that we put into the atmosphere and increasing the amount that's removed from the atmosphere in one way or another.

- No other industry can do what these forests are doing.

It's the most effective and efficient way to store carbon at scale.

- So is there a way to have more trees on planet earth without the vulnerable 20 year period that it takes for young trees to reach maturity?

Well, it turns out there are a few ways to increase the number of trees taking up carbon.

In a new study, Tom and his team created a model of global forest carbon storage.

He found that forests have the potential to store about a third of the carbon that humans have released in the atmosphere since the Industrial Revolution.

Removing that much carbon from the atmosphere would be game changing, and most of this potential lies in existing forests.

- The conservation of existing forests is our most powerful carbon drawdown tool, allowing those ecosystems to regenerate.

This cannot be achieved though through mass plantations because the power of nature is in its complexity.

- You can hear the rest of Tom's story and NOVA's new documentary, Secrets of the Forest.

But the point is a lot of the focus isn't on existing forests.

Bev studied this as well by comparing three ways to increase forest carbon.

Afforestation, which is planting trees in places where trees have not recently grown, like retired agricultural land.

Reforestation, which is planting trees in places where trees did recently grow, like after a clear cut or a landslide, for example.

And simply preventing trees from being cut down.

- The most effective, many times more, was to reduce harvest on public lands by about half.

- So to skip the first 20 years of waiting for trees to absorb carbon, her study points to protecting existing forests.

But much of the forest cut in the US is harvested for timber products.

And Bev's research shows that by increasing the harvest interval from around 40 to 45 years to 80 or 90 years, we can increase the carbon storage and still get the wood products that we all use and enjoy.

- And let them grow to 80 years instead of 40, 45 years.

- On the surface tree planting efforts like the Trillion Tree campaign seem like a great step forward in our efforts to decarbonize.

But with a little more context, it's easy to see how it's not quite that simple.

It's clear that planting trees while pumping fossil fuels into the atmosphere isn't the best strategy.

Much like working out while eating junk food doesn't necessarily make you healthy.

Instead, it seems that the best step forward is to preserve our forests that already serve as vital carbon sinks while working to lower our overall carbon emissions through many of the strategies that we've explored on the show.

Oh, and thanks to NOVA for being a part of this episode.

Be sure to check out their full film Secrets of the Forest.