The distinguished physicist Freeman Dyson (1923–2020) once remarked that dotting the globe with great swaths of saplings would prove an excellent way to counter global warming. Now, a new study has calculated the scale of the new forests required to offset the massive carbon footprints of Bitcoin, Ethereum, and a number of other cryptocurrencies. The source is Forex Suggest, a South Africa–based site that provides education on trading and financial markets. Its Global Impact of Crypto Trading report finds that erasing the pollution spewed by Bitcoin mining would require by far the biggest expansion of the world’s forests, versus Ethereum and the other cryptos. The reason is basic: Bitcoin uses multiples of the amount of electricity deployed by each of its rivals. The signature coin will burn roughly 76 billion kWh this year, nearly triple the consumption of Ethereum, and over 100 times that of Litecoin.

All told, Bitcoin emits—by Forex Suggest’s estimate—some 57 million tons of CO2 annually, more than double Ethereum’s footprint. It’s noteworthy that for Bitcoin, all that energy generates a relatively low number of transactions. Because its distributed network is so slow, its users post only around 12,000 purchases, sales, and transfers on the blockchain each hour. That’s approximately 115 million transactions a year. By contrast, Ethereum handles over four times those volumes—devouring, once again, far less than half the juice. The result: Bitcoin deploys an incredible 707 kWh of electricity per transaction, 11 times as much as Ethereum, and emits 1,061 pounds, or half a ton, of CO2 every time you tap the app to buy a latte or zap a fraction to a buddy who beat you on a golf bet. Ethereum sends less than one-tenth of that carbon skyward for each purchase or transfer it processes.

So how many new trees would it take to swallow all the CO2 that Bitcoin gushes each year? Forex Suggest puts the number at 284 million. That’s a lot of greenery. Central Park hosts 18,000 maples, spruces, and the like. New Jersey, an extremely rural state, by the way, is home to 806 million trees. Compensating for Bitcoin’s pollution would require installing new root balls equaling one-third the leaf-crowned trunks gracing the Garden State, and 4% of the forests of California.

Forex Suggest based its projections on saplings planted in the tropics, where they sprout fast, baking in extras for the trees that die or fail to reach their potential for carbon sequestration.

In 2007, Dyson—a legend on quantum electrodynamics and nuclear engineering at the Institute for Advanced Study in Princeton—wrote that “it would be possible in the case of a worldwide emergency to plant enough trees and other fast-growing plants to absorb the excess CO2 and bring the annual increase to a halt.” At the time, Bitcoin wasn’t adding to the problem. It would be fascinating to learn how Dyson would rate an invention offering no practical uses that greatly increases the forested expanses needed just to keep greenhouse gas emissions the same, let alone reduce them. As a scientist who broke new ground, he might be marveling at how a brainchild that pollutes to exist ever took hold.