How Many Trees Are Needed to Offset CO2?

Written By Teacher: Elizabeth Ward

My name is Elizabeth Ward. I am a former Early Childhood, Elementary, and English as a Foreign Language educator. I have taught third grade Science and Social Studies as well as Kindergarten in both urban and rural Oklahoma public schools. I taught online EFL to students of all ages in China for four years. I also have experience in curriculum development and content design for teachers in the physical and digital classroom. As a former teacher I have a passion for supporting teachers and making their jobs easier. I currently live in the greater Houston area with my husband and four dogs. 

As teachers, we know that introducing students to the role of trees in our environment can be inspiring yet complex. Trees are essential for maintaining ecological balance and regulating climate. Explaining their impact, however, requires careful planning. Resources that illustrate trees’ contributions to our planet’s health can make this topic more engaging. Early childhood teachers can teach this lesson on the Importance of Trees while secondary educators may facilitate discussion using the resource How Trees Talk to Each Other.  These tools help students understand the importance of trees in our ecosystem and daily life. 

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.

As trees grow, they take in carbon from the air and store it in wood, plant matter, and in the soil, making them what scientists call “carbon sinks.” In this way, forests play an important role in the global carbon cycle by soaking up lots of carbon dioxide (CO2) that would otherwise live in the atmosphere. Could we plant enough trees to absorb the amount of CO2 that Americans create and, in theory, cancel out our planet-warming carbon emissions?

It’s tempting to think that a back-of-the-envelope calculation can deliver a useful answer. For example, in 2021, the U.S. emitted about 5.6 billion tons of CO2 and other greenhouse gases. A hectare of trees, meanwhile, might hold around 50 tons of carbon, equivalent to around 180 tons of CO2 in the atmosphere. At this rate, it would take a little over 30 million hectares of trees to account for one year of American emissions—or a forest roughly the size of New Mexico. (For context, the United Nations estimates that there are about 4 billion hectares of forest on Earth right now.)

So that’s the answer, right?

Well, no. In reality, the carbon math is much messier. For one thing, the type and age of the trees matters enormously. Studies of different forests have found that some store not much more than 10 tons of carbon per hectare, while others store well over 1,000. Our rough estimate of 50 tons per hectare would not be uncommon for a young-ish forest in North America, according to figures from the U.S. Forest Service, but the details matter.