[0:07]Standing at almost 84 meters tall, this is the largest known living tree on the planet.
[0:14]Nicknamed General Sherman, this giant sequoia has sequestered roughly 1,400 tons of atmospheric carbon over its estimated 2,500 years on Earth.
[0:27]Very few trees can compete with this carbon impact, but today, humanity produces more than 1,400 tons of carbon every minute.
[0:37]To combat climate change, we need to steeply reduce fossil fuel emissions and draw down excess CO2 to restore our atmosphere's balance of greenhouse gases.
[0:49]But what can trees do to help in this fight and how do they sequester carbon in the first place?
[0:56]Like all plants, trees consume atmospheric carbon through a chemical reaction called photosynthesis.
[1:02]This process uses energy from sunlight to convert water and carbon dioxide into oxygen and energy storing carbohydrates.
[1:11]Plants then consume these carbohydrates in a reverse process called respiration, converting them to energy and releasing carbon back into the atmosphere.
[1:21]In trees, however, a large portion of that carbon isn't released and instead is stored as newly formed wood tissue.
[1:30]During their lifetimes, trees act as carbon vaults, and they continue to draw down carbon for as long as they grow.
[1:39]However, when a tree dies and decays, some of its carbon will be released back into the air.
[1:45]A significant amount of CO2 is stored in the soil, where it can remain for thousands of years, but eventually, that carbon also seeps back into the atmosphere.
[1:56]So if trees are going to help fight a long-term problem like climate change, they need to survive to sequester their carbon for the longest period possible, while also reproducing quickly.
[2:08]Is there one type of tree we could plant that meets these criteria?
[2:11]Some fast-growing, long-lived, super sequestering species we could scatter worldwide.
[2:19]Not that we know of. But even if such a tree existed, it wouldn't be a good long-term solution.
[2:25]Forests are complex networks of living organisms, and there's no one species that can thrive in every ecosystem.
[2:33]The most sustainable trees to plant are always native ones, species that already play a role in their local environment.
[2:41]Preliminary research shows that ecosystems with a naturally occurring diversity of trees have less competition for resources and better resist climate change.
[2:51]This means we can't just plant trees to draw down carbon.
[2:54]We need to restore depleted ecosystems.
[2:58]There are numerous regions that have been clear cut or developed that are ripe for restoring.
[3:05]In 2019, a study led by Zurich's Crowther Lab analyzed satellite imagery of the world's existing tree cover.
[3:13]By combining it with climate and soil data and excluding areas necessary for human use, they determined Earth could support nearly 1 billion hectares of additional forest.
[3:26]That's roughly 1.2 trillion trees.
[3:29]This staggering number surprised the scientific community, prompting additional research.
[3:35]Scientists now cite a more conservative but still remarkable figure.
[3:40]By their revised estimates, these restored ecosystems could capture anywhere from 100 to 200 billion tons of carbon, accounting for over 1/6th of humanity's carbon emissions.
[3:53]More than half of the potential forest canopy for new restoration efforts can be found in just six countries.
[4:01]And the study can also provide insight into existing restoration projects, like the Bon Challenge, which aims to restore 350 million hectares of forest by 2030.
[4:13]But this is where it gets complicated. Ecosystems are incredibly complex, and it's unclear whether they're best restored by human intervention.
[4:22]It's possible the right thing to do for certain areas is to simply leave them alone.
[4:28]Additionally, some researchers worry that restoring forests on this scale may have unintended consequences, like producing natural biochemicals at a pace that could actually accelerate climate change.
[4:41]And even if we succeed in restoring these areas, future generations would need to protect them from the natural and economic forces that previously depleted them.
[4:53]Taken together, these challenges have damaged confidence in restoration projects worldwide.
[4:59]And the complexity of rebuilding ecosystems demonstrates how important it is to protect our existing forests.
[5:07]But hopefully, restoring some of these depleted regions will give us the data and conviction necessary to combat climate change on a larger scale.
[5:16]If we get it right, maybe these modern trees will have time to grow into carbon-carrying Titans.
[5:23]But exactly how tall can a tree grow if there's plenty of sun and carbon?
[5:29]What stops a tree from growing more than 130 meters tall?
[5:33]Check out this video to see what's getting in the way, or delve into the Earth to learn more about the fascinating way trees communicate.
