How many new trees would we need to offset our carbon emissions?
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.1 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.2)
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 1,000.3 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.4
