Why Don't We Just Plant A Lot Of Trees?

Written By Teacher: Meighan Hooper

Meighan has been an arts educator and instructional designer since 2007. Originally from Ontario, Canada, she began teaching internationally in the Middle East and Asia in 2013. Meighan has designed programs of study based on a variety of curriculum including Canadian, American standards-based, Primary Years Program (IB), and British National curriculum.

Start with this question to spark a discussion with your students about the scale of carbon emissions and why planting trees alone can’t fully address climate change. This is a great opportunity to connect it to lessons on photosynthesis and the life cycle of trees, helping students understand how these natural processes play a role in broader climate solutions. For middle school, the "Carbon Cycle Game" offers an interactive way to explore how carbon moves through ecosystems, including forests. For elementary students, the "Science Lesson: Carbon Sequestration" introduces how trees and soils store carbon, helping younger learners grasp the importance of natural systems in combating climate change.

Written By: MIT Environmental Solutions Initiative

The MIT Climate Change Engagement Program, a part of MIT Climate HQ, provides the public with nonpartisan, easy-to-understand, and scientifically-grounded information on climate change and its solutions.

It’s well understood that the carbon dioxide (CO2) we’re emitting into the atmosphere is causing the planet to warm. We also know that trees absorb CO2. So why not plant enough trees to take back all the CO2 we’re dishing out? Unfortunately, “while the idea sounds nice and definitely helps to some extent, we will never be able to counterbalance the amount of fossil fuels we burn by only growing trees,” says Charles Harvey, MIT Professor of Civil and Environmental Engineering, who specializes in environmental management.

As trees grow, they take in CO2 from the air and incorporate the carbon into their leaves, trunks, and roots, as well as the soil under them. The soil carbon remains even after the trees themselves die. So it makes sense to plant trees to reduce the CO2 in the atmosphere. Several scientific papers have supported mass tree-planting as a way to store more carbon in soil, otherwise known as carbon sequestration. Recently, some have taken this logic to an extreme: a bill titled the Trillion Trees Act introduced in the U.S. Congress aims to plant one trillion trees by 2050. But “there are several issues with this bill, and nearly every single environmental organization in the U.S. co-signed a letter of opposition,” says Harvey. “The main issue is that this bill distracts from needed reductions in fossil fuel emissions.”

If we think of planting trees as a stand-alone action to fight climate change, we will run into some hard limits on how much CO2 they can store. “The process of growing trees to store carbon isn’t as straightforward as ‘take in carbon, export oxygen,’” says Harvey. “Forests have metabolisms just like us, and as they approach maturity, forests reach an equilibrium where they are carbon neutral.” In other words, trees are not simply a sink of carbon from the atmosphere. In mature forests, the uptake of CO2 by photosynthesis is balanced by the release of CO2 back to the atmosphere, through decay of wood and leaves, consumption by insects and animals, and respiration within the trees themselves.

It’s well understood that the carbon dioxide (CO2) we’re emitting into the atmosphere is causing the planet to warm. We also know that trees absorb CO2. So why not plant enough trees to take back all the CO2 we’re dishing out? Unfortunately, “while the idea sounds nice and definitely helps to some extent, we will never be able to counterbalance the amount of fossil fuels we burn by only growing trees,” says Charles Harvey, MIT Professor of Civil and Environmental Engineering, who specializes in environmental management.

As trees grow, they take in CO2 from the air and incorporate the carbon into their leaves, trunks, and roots, as well as the soil under them. The soil carbon remains even after the trees themselves die. So it makes sense to plant trees to reduce the CO2 in the atmosphere. Several scientific papers have supported mass tree-planting as a way to store more carbon in soil, otherwise known as carbon sequestration. Recently, some have taken this logic to an extreme: a bill titled the Trillion Trees Act introduced in the U.S. Congress aims to plant one trillion trees by 2050. But “there are several issues with this bill, and nearly every single environmental organization in the U.S. co-signed a letter of opposition,” says Harvey. “The main issue is that this bill distracts from needed reductions in fossil fuel emissions.”

If we think of planting trees as a stand-alone action to fight climate change, we will run into some hard limits on how much CO2 they can store. “The process of growing trees to store carbon isn’t as straightforward as ‘take in carbon, export oxygen,’” says Harvey. “Forests have metabolisms just like us, and as they approach maturity, forests reach an equilibrium where they are carbon neutral.” In other words, trees are not simply a sink of carbon from the atmosphere. In mature forests, the uptake of CO2 by photosynthesis is balanced by the release of CO2 back to the atmosphere, through decay of wood and leaves, consumption by insects and animals, and respiration within the trees themselves.