The vast network of computer hardware that keeps the Bitcoin network running requires a staggering amount of energy. That has led to concerns about the cryptocurrency’s effect on the environment. But assessing Bitcoin’s actual, bottom-line impact is not as simple as it might seem, say experts.
Bitcoin’s huge computational demands are the result of a process known as “mining.” Participants race to solve complex mathematical problems for the right to verify the next “block” of transactions and claim a reward of freshly minted bitcoins. The system requires considerable processing power and is designed to make tampering with records extremely hard. The puzzles’ difficulty also increases with the number of miners—roughly correlating to the incentive for mining, which often tracks with bitcoin price. Resulting in a bottom line that as new miners pile in, new blocks are produced at reliably the same rate.
With the price of a bitcoin currently surging, the issue is coming to the forefront again.
These days, solving those mathematical puzzles has become so tricky that most mining is done by companies running energy-hungry data centers full of specialized chips. Several studies have suggested the carbon footprint of all this computation could be equivalent to that of a small country. Late last year, research in Cell Reports Sustainability also highlighted Bitcoin’s water use, estimating that it gets through roughly 2.2 trillion liters a year. And with the price of a bitcoin currently surging, the issue is coming to the forefront again.
The shadowy nature of cryptocurrencies makes accurate assessments difficult though, experts say. In particular, there’s considerable uncertainty around the hardware and energy sources miners are using. That leaves wide margins of error when estimating Bitcoin’s energy use and how that translates into environmental impacts, says Alexander Neumüller, a research associate at the Cambridge Centre for Alternative Finance at the University of Cambridge. “It’s a decentralized network, so you really don’t know what everyone is doing,” he says.
How actually big is big?
While settling on a figure may be hard, there’s little doubt Bitcoin uses a huge amount of electricity, says Alex de Vries, a data scientist at the Dutch central bank who is pursuing a Ph.D. in cryptocurrency sustainability at VU Amsterdam in the Netherlands. He is the author of the recent paper on Bitcoin’s water use and has published several studies on the cryptocurrency’s energy footprint.
Estimating Bitcoin’s power bill is easier than many other computing applications, says de Vries. There is a public record of how many guesses miners have made in their attempts to solve Bitcoin’s cryptographic puzzles. This so-called “hash rate” provides a proxy for the networks total computational power, which can be combined with performance data from the most popular mining chips to approximate energy use, says de Vries.
“Anyone that really understands the industry knows that there’s this immense drive to the lowest-cost power source.”
—Murray Rudd, Satoshi Action Education
Where things get fuzzier is translating that into carbon emissions. Most papers so far have relied on using miners’ IP addresses to judge their location and then looking at what energy sources supply the grid in that region. A recent paper from researchers at the United Nations University in Hamilton, Canada, using this approach estimated that roughly 67 percent of Bitcoin’s energy use between 2020 to 2021 came from fossil fuels, thanks mainly to miners in coal-reliant countries like China, Kazakhstan, and Russia. Their calculated result was 85.89 megatonnes of CO2 equivalent being emitted in that two-year period. For comparison, Denmark produced 45.80 megatonnes in 2022.
A similar approach can help estimate Bitcoin’s water footprint, because most of the network’s water use traces back to electricity generation. The U.N. researchers predict that in the same period Bitcoin used 1.65 trillion liters of water, equivalent to more than 660,000 Olympic-size swimming pools. In his paper, de Vries estimate pegs the figure for 2023 even higher, at 2.2 trillion.
This kind of analysis betrays a lack of understanding of the mining industry though, says Murray Rudd, an environmental economist at Satoshi Action Education, a U.S. nonprofit that advocates for Bitcoin. “Anyone that really understands the industry knows that there’s this immense drive to the lowest-cost power source,” he says.
This means miners typically set up in regions with especially cheap energy or sign bespoke deals with energy providers. In many cases this low-cost power comes from renewables, he says, like excess hydropower and increasingly solar and wind as their prices continue to plummet. Some miners also rely on “stranded energy” like waste methane from oil wells and landfills. The potent greenhouse gas is normally burned to convert it into less harmful CO2 that is then released into the atmosphere. Instead, it can be used as a carbon-neutral source of power for miners, says Rudd.
Studying the studies
Assessing how these trends affect Bitcoin’s environmental impact is difficult due to the paucity of peer-reviewed research on the topic, says Rudd. That’s why he recently coauthored a paper outlining some of the key unanswered research questions in this area. “There’s no doubt Bitcoin mining uses a huge amount of electricity,” says Rudd. “The question really is what type of energy and what are the longer-term impacts of that energy use?”
With the cost of renewables continuing to fall, it’s likely miners will shift to greener power sources over time, he says. Proponents of Bitcoin have even suggested it could promote the development of renewables. It’s difficult to integrate large amounts of solar and wind power into grids, because their intermittency makes it tricky to balance supply and demand. But Bitcoin mines can provide so-called “demand response” to grid operators by switching off during demand spikes in exchange for a fee, says Rudd. The Electric Reliability Council of Texas already has several such agreements with miners to help balance the state’s renewables-heavy grid.
“If the bitcoin price is cut in half, by next week most of the industry will be gone. It’s just not a very stable foundation for a long-term renewable energy project.”
—Alex de Vries, VU Amsterdam
Some have also suggested Bitcoin mines could provide a way to monetize renewables’ developments before they are connected to the grid, which can sometimes take years. Fengqi You, a professor of energy systems engineering at Cornell University, investigated the proposal in a paper published last October. Whether or not a project could benefit depends on a host of factors such as size, location, and local regulation, says You. But in Texas they showed that 32 planned renewable installations could generate combined profits of US $47 million while waiting to connect to the grid.
“If you can have some of these wasted renewable resources generate some economic value, that could in turn offset the cost of renewables and fundamentally help us support the development of renewables projects,” he says.
However, de Vries thinks it’s unlikely developers would factor this into their planning. Most renewables projects are planned many years in advance, but the highly volatile price of a bitcoin means the economics of mines can change rapidly. “If the bitcoin price is cut in half, by next week most of the industry will be gone,” he says. “It’s just not a very stable foundation for a long-term renewable energy project.”
Renewable energy is also a scarce resource, he says, so using it to power Bitcoin mining slows the decarbonization of other sectors of the economy. And crucially, when new demand comes online, this is normally met by gas plants that can be quickly ramped up and down. That means that when miners come to town it’s actually more likely to boost fossil fuel use than the regional energy mix suggests, says de Vries.
Getting to the bottom of this issue is tough, says Cambridge’s Neumüller. He leads the Cambridge Bitcoin Electricity Consumption Index (CBECI) project, which provides continually updated estimates of Bitcoin’s energy use and climate impact. The index gives figures for the best- and worst-case scenarios, but its current “best guess” estimate pegs Bitcoin’s annual CO2-equivalent emissions at 77.98 megatonnes.
Data centers consume roughly 1 percent of the world’s energy, but they provide clear benefits. Some experts are skeptical whether Bitcoin can say the same.
Neumüller concedes that the reliance on national energy mixes is a limitation, but he says getting more granular data is hard. He also notes that their calculations are based on location data from 2022. Since then, many miners have moved out of China and Kazakhstan, and he expects an update due later this year will result in significant shift in emissions intensity. It’s important that someone attempts to estimate the scale of these issues though, he says, even if the results are a little rough. “Otherwise, you will be completely in the dark,” he adds.
However, most efforts to predict Bitcoin’s energy use make the same mistake, says Jonathan Koomey, a consultant and widely quoted expert on computing’s energy footprint. They assume that electricity use grows proportionally to the computational demand. In reality, he says, as technology is deployed at scale it typically becomes significantly more efficient, so energy use doesn’t rise nearly as quickly.
Nonetheless, there’s little doubt that the energy use is significant, says Koomey. But debate about its scale is ultimately irrelevant until society settles a more important question—is it worth it? Data centers consume roughly 1 percent of the world’s energy, Koomey says, but they provide clear benefits. He’s skeptical whether Bitcoin can say the same. “The actual use cases are not anywhere near justifying the energy and other impacts,” he says.
Another significant elephant in the room, Koomey adds, is the fact that it’s perfectly possible to build a cryptocurrency that doesn’t require energy-hungry mining. Last year, the second largest cryptocurrency Ethereum abandoned the practice in favor of an alternative approach called proof of stake, in which users win the right to mint new blocks by putting up large chunks of their holdings as collateral. The switch reduced the networks energy use by 99.9 percent almost overnight.
The idea is anathema to many Bitcoin advocates who argue that the approach is less secure and more open to manipulation. But Ethereum’s continued success makes it increasingly difficult to justify Bitcoin’s energy footprint, says Koomey.
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Edd Gent is a freelance science and technology writer based in Bengaluru, India. His writing focuses on emerging technologies across computing, engineering, energy and bioscience. He's on Twitter at @EddytheGent and email at edd dot gent at outlook dot com. His PGP fingerprint is ABB8 6BB3 3E69 C4A7 EC91 611B 5C12 193D 5DFC C01B. His public key is here. DM for Signal info.