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Late on Wednesday, Elon Musk went back on his previous decision to let buyers pay for Tesla cars using Bitcoin. His reason: Mining the digital currency is taking its toll on the environment.

The Tesla CEO’s reversal, made on Twitter, led to a steep fall in the value of Bitcoin, with over $365 billion in market value wiped off BTC at one point on Thursday.

Tesla & Bitcoin pic.twitter.com/YSswJmVZhP
— Elon Musk (@elonmusk) May 12, 2021

Cue outrage from Bitcoin bulls. “All of a sudden, he’s not so keen due to environmental concerns. But why now?” fumed Nigel Green, CEO of financial adviser, deVere Group, a noted cryptocurrency booster. “Those issues surrounding the environmental impact have not come up in the last few months.”

Be that as it may, but Musk’s warning has a point—one that been raised repeatedly by environmentalists and ESG investing hawks since Tesla in March said it would accept crypto as payment.

Even Wall Street agrees there’s ample evidence pointing to Bitcoin mining as a bad deal for the environment. In a recent investor note, BofA Securities set out to calculate the costs on the planet.

Here’s what they found:

Carbon emissions

According to the report, rising Bitcoin prices have led to an “astronomical” surge in CO2 emissions. Over the past two years, the historic rise of Bitcoin has caused emissions to increase by over 40 million tons—equivalent to 8.9 million cars added to the road, the BofA report said.

Dirtier than airlines

The BofA report also found that Bitcoin produces more carbon emissions than American Airlines, one of the largest airlines in the world with over 200 million passengers in an ordinary year. Bitcoin’s emissions are also comparable to those of the U.S. federal government, which employs over 2 million people.

If Bitcoin were a country

If that is not proof enough. Consider this: Mining the currency emits more CO2 than the whole of Greece. And that could worsen. If the price of Bitcoin were to rise to $1 million, BofA calculates, the digital currency could turn into the fifth largest CO2 emitter in the world, surpassing Japan.

An expensive rally

If $1 billion of hard cash went into the currency, and its value rose by 11%, that would cause the CO2 footprint to rise by 5.4 million tons—equivalent to 1.2 million cars.

And finally, the BofA report said that no other human activity has a higher carbon footprint—that is, per dollar invested. It’s equivalent to powering 632,000 homes with electricity.

When Musk first made the announcement to accept Bitcoin as payment for Tesla back in March, there was instant backlash from critics who noted the hypocrisy of the “low-carbon” Tesla accepting the high-emission currency.

But even if Musk went for an alternative, BofA notes that other crypto assets are only slightly better. Ethereum, the second largest cryptocurrency, has seen its energy consumption double from eight terawatt-hours (TWh) to 17 TWh in the six months it took to see its currency rise to $2,000.