Given the complexity of climate change, the solution isn't straightforward. However, what is important is not only planting more trees but also preventing existing forests from being destroyed.
Climate change concerns are now front and center for a great many people. For those who have recently turned their attention to climate solutions, one of the first questions asked is, “How many trees would it take to save the planet?”
It’s a reasonable question. After all, massive deforestation of the developing world and the potential collapse of the Amazon rainforest ecosystem have been headline topics for several decades. And planting trees is easy to understand. Everyone knows what trees are, and the basic processes of photosynthesis and respiration are taught in elementary school. Young children learn that trees breathe carbon dioxide in and oxygen out. It’s also human nature to consider the simplest solutions first before moving on to more complex solutions.
The simple truth is we need to plant many more trees to combat climate change. But like every climate solution, that is where the complexity begins.
How many trees are planted each year on a global basis?
To put the answer to this question in context, first we need to understand how many trees are on Planet Earth. Data published in 2015 estimated there are about three trillion trees on Planet Earth.[1] Of these, over 15 billion trees are cut or burned down each year, and the number of trees in the world has fallen by about 46% since the dawn of human civilization. Currently, about 1.8 billion trees are being planted per year[2] which is a great effort. But the inescapable truth is that we are losing far more trees per year than we are planting.
So we need to preserve our remaining forests with just as much urgency as our efforts to plant trees. Then, we need to consider that many of these trees are being planted for the purpose of harvesting them, so they will need to be replaced. Finally, global warming itself is a threat to trees – drought, fire, pests, and other risks exacerbated by global warming currently kill millions of trees. As we experience more severe impacts from climate change, more trees will die faster. As University of Arizona ecohydrologist David Breshears says, “the warming we’re trying to slow is killing the trees.”[3]
What is the climate impact of planting trees?
We love planting trees because we admire their beauty, ecosystem benefits, and their ability to sequester carbon dioxide. The average tree absorbs about 10 kilograms, or 22 pounds, of CO₂ each year for the first 20 years.[4]
So, how many trees would it take to save the planet? Every year, humans emit around 38 billion metric tons of CO₂.[5] Of these emissions, about 55% are absorbed by the land and ocean,[6] leaving us with a balance of 21 billion tons of CO₂ in the atmosphere each year. So, to plant enough trees to offset these emissions each year, we would need around 2.1 trillion new trees. Is this feasible? Let’s do the math.
There are about 2.2 billion acres of land available for new trees.[7] Given a planting density of 500 trees per acre,[2] this means we can plant another 1.1 trillion trees. Collectively, these trees would absorb 11 billion metric tons of CO₂ each year if able to survive.
So, it’s a great idea to plant a trillion trees, but in order to make it worthwhile, we must steward them to ensure their long term health. Otherwise, we’re just opening ourselves up to more wildfires like the ones across Canada this year and more air pollution filling our lungs.
It is also worth noting that while trees absorb CO₂, which will ultimately make the planet cooler, they also have an effect on local temperatures depending on their location. Boreal forests have a mild cooling effect in the summer and strong warming effect in the winter, temperate forests exhibit a strong cooling effect in the summer and mild warming effect in the winter, and tropical forests exhibit a strong cooling effect throughout the year.[8] In a world with a trillion more trees, many of which will be planted in mid and high-latitude regions, we should expect even faster-warming winters.
Conclusion
So, how many trees would it take to save the planet? Right now it would take 2.1 trillion trees. This is roughly twice the 1.1 trillion we’re currently able to find space for.
But what about a future in which we stop cutting down 15 billion trees a year, decarbonize the entire economy, and only have legacy emissions to clean up? Will planting trees be enough? Well, it’s not exactly clear. Anyone can plant seeds, but it takes ongoing care to help them grow. And who is going to take care of 2.2 billion new acres of forest? Who will ensure their health and protect them from being logged? Who can stop a wildfire?
There are many questions and huge potential risks in adding more wood to an already burning world. And with so many other durable carbon removal solutions currently in development, perhaps it’s best not to put all our molecules into one method.
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Sources:
[1] Crowther, T., Glick, H., Covey, K. et al. (2015). Mapping tree density at a global scale. Nature 525, 201–205. https://doi.org/10.1038/nature14967
[2] Tree Vitalize. (2023). “Tree Planting Statistics.” https://treevitalize.com/tree-planting-statistics/
[3] Berwyn, Bob. (May 27, 2020). “Can Planting a Trillion Trees Stop Climate Change? Scientists Say it’s a Lot More Complicated.” Inside Climate News, Politics & Policy. https://insideclimatenews.org/news/27052020/trillion-trees-climate-change/
[4] One Tree Planted. (July 25, 2023). How much CO2 does a tree absorb? One Tree Planted. https://onetreeplanted.org/blogs/stories/how-much-co2-does-a-tree-absorb
[5] Our World in Data. (2023). "CO2 and Greenhouse Gas Emissions." https://ourworldindata.org/co2-and-greenhouse-gas-emissions
[6] Friedlingstein, P., O'sullivan, M., Jones, M. W., Andrew, R. M., Gregor, L., Hauck, J., ... & Zheng, B. (2022). Global carbon budget 2022. Earth System Science Data, 14(11), 4811-4900. doi.org/10.5194/essd-14-4811-2022
[7] Bastin, J.F. et al. (2019). The global tree restoration potential. Science 365, 76-79. doi:10.1126/science.aax0848
[8] Li, Yan & Zhao, Maosheng & Motesharrei, Safa & Mu, Qiaozhen & Kalnay, Eugenia & Li, Shuangcheng. (2015). Local cooling and warming effects of forests based on satellite observations. Nature communications. 6. 6603. https://doi.org/10.1038/ncomms7603