In the last five years, numerous US corporations have made commitments to offset their carbon footprint, sometimes by tree planting. Microsoft wants to be ‘carbon negative’ by 2030,¹ and Google – which has been carbon neutral since 2007 – wants to be carbon-free by 2030.² Amazon has committed to net-zero carbon by 2040, and Starbucks has pledged to “give more than we take from the planet”.³

But, how do these corporations plan to offset their carbon footprint? What do these commitments mean? 

How much carbon is offset by planting a tree?

Trees absorb carbon dioxide and store it as organic matter throughout their lifetime. The amount of carbon that a tree absorbs depends on its species, location and weather. For example, a silver maple tree will absorb around 400 pounds of carbon dioxide over 25 years, according to the U.S. Energy Information Administration (EIA).⁴

A tropical tree absorbs an average of 50 pounds of carbon dioxide per tree annually, according to some scientists.⁵ These figures provide us with a rough idea of how much carbon is offset by planting a tree.

Does planting trees really offset carbon?

Trees offset carbon by absorbing it and storing it in the form of organic material. But they cannot remove the CO2 from our atmosphere permanently.⁶ To understand why this is the case, we need to examine the process more closely.

Plant cells absorb sunlight and carbon dioxide from the air. Through photosynthesis, they turn it into oxygen and organic material. A tree uses organic carbon material to build its structure, including the roots, leaves and trunk. When a tree dies, a lot of that stored carbon returns to the atmosphere through decomposing. But a tree can live for over a thousand years and decompose for another few hundred years. It captures the carbon for all that time.⁷

Moreover, older trees absorb more carbon dioxide than younger ones. This is because they need more organic material to grow and sustain themselves. So cutting down trees and planting new ones may lead to more carbon being emitted than being offset.⁸

How many trees would I need to plant to be carbon neutral?

An average American emits around 15 metric tonnes of carbon dioxide per year.⁹ A tree is estimated to absorb around one tonne of carbon over its lifetime of about 100 years.¹⁰ Hence, an American resident would need to plant at least 15 trees a year, and ensure that they survive for decades to offset their carbon emissions. This number would be lower for people in other countries where emissions per head are lower.

Some companies allow people to offset their carbon for specific events. For example, a person would burn about 0.29 metric tonnes of carbon for a flight from New York to Los Angeles. Some companies provide people with the option to pay to offset their carbon by planting trees, for example. Offsetting emissions from a flight can cost as little as USD $4.¹¹

1. Nguyen, T. (2020). More companies want to be “carbon neutral.” What does that mean? [online] Vox. Available at: https://www.vox.com/the-goods/2020/3/5/21155020/companies-carbon-neutral-climate-positive.
2. Google Sustainability. (2017). Our Commitments | Google Sustainability. [online] Available at: https://sustainability.google/commitments/.
3. Nguyen, T. (2020). More companies want to be “carbon neutral.” What does that mean? [online] Vox. Available at: https://www.vox.com/the-goods/2020/3/5/21155020/companies-carbon-neutral-climate-positive.
4. Sierra Club. (2018). How much carbon do trees really store? [online] Available at: https://www.sierraclub.org/sierra/2016-2-march-april/ask-mr-green/how-much-carbon-do-trees-really-store.
5. University of New Mexico.(n.d.). How to calculate the amount of CO2 sequestered in a tree per year. [online] Available at: https://www.unm.edu/~jbrink/365/Documents/Calculating_tree_carbon.pdf.
6. Marshall, M. (2020). Planting trees doesn’t always help with climate change. [online] www.bbc.com. Available at: https://www.bbc.com/future/article/20200521-planting-trees-doesnt-always-help-with-climate-change.
7. Penn State Extension. (2020). How Forests Store Carbon. [online] Available at: https://extension.psu.edu/how-forests-store-carbon.
8. Imperial News. (2020). Q&A: Is planting trees the answer to climate change? | Imperial News | Imperial College London. [online] Available at: https://www.imperial.ac.uk/news/199473/qa-is-planting-trees-answer-climate/.
9. Bewicke, H. (2019). Chart of the day: These countries have the largest carbon footprints. [online] World Economic Forum. Available at: https://www.weforum.org/agenda/2019/01/chart-of-the-day-these-countries-have-the-largest-carbon-footprints/.
10. Institute, G. (2015). How much CO2 can trees take up? [online] Climate & Environment at Imperial. Available at: https://granthaminstitute.com/2015/09/02/how-much-co2-can-trees-take-up/.
11. Mock, J. and Tabuchi, H. (2019). How to Buy Carbon Offsets. The New York Times. [online] 24 Jul. Available at: https://www.nytimes.com/2019/07/24/climate/nyt-climate-newsletter-carbon-offsets.html.