Blockchain’s climate impact depends chiefly on how a network reaches agreement on transactions. Proof-of-work systems such as Bitcoin use electricity-intensive mining; proof-of-stake systems such as Ethereum use a different mechanism and can require far less electricity. Electricity use is not the same as greenhouse-gas emissions: emissions also depend on where a network’s computing takes place and the electricity sources used there.
How blockchain can contribute to emissions
Blockchain networks maintain a shared record of transactions without relying on one central operator. Their computers, or nodes, communicate and follow rules for agreeing on new records. The consensus mechanism—the process used to validate transactions and secure the network—shapes how much computing and electricity that work requires.
As an Amazon Associate I earn from qualifying purchases.
Proof-of-work uses electricity as part of its security model
In proof-of-work (PoW), miners compete by performing computational work to propose and validate blocks. The International Energy Agency described this electricity use as both a security feature and a side effect of relying on competing miners’ computing power. The more energy-intensive process is therefore part of how PoW secures a network, not simply electricity used to run a conventional payment database. IEA’s explanation of Bitcoin’s energy use.
Free tools Windows power users keep installed
One-click scans. No signup required.
Proof-of-stake changes the work required
Proof-of-stake (PoS) uses a different approach to validating blocks. Instead of a competition based on computational work, the system relies on participants who stake cryptocurrency to help validate the network. Ethereum’s documentation explains that PoW is more energy-hungry because electricity is consumed in the mining process. A change in consensus can therefore change a network’s electricity demand substantially, although one network’s results should not be assumed to represent all PoS chains. Ethereum.org’s proof-of-stake FAQ.
#1 Best Overall
Why electricity use and global warming are not interchangeable
A network’s electricity consumption measures energy demand. Its greenhouse-gas emissions estimate depends additionally on the electricity sources serving its computing and where that computing is located. Electricity generated with lower-carbon sources generally produces different emissions than electricity generated with higher-carbon sources, so two networks with similar energy use could have different estimated emissions.
Cambridge’s Bitcoin emissions methodology treats electricity consumption and emissions as separate analytical steps, incorporating mining geography and regional energy sources. Its estimates also depend on model assumptions and location data. The Cambridge index uses a seven-day moving average to reduce short-term hashrate volatility; that smoothing does not eliminate uncertainty in the underlying inputs. Cambridge’s Bitcoin GHG emissions methodology.
What published estimates show—and what they do not
Bitcoin: treat the IEA figures as historical
In a 2019 commentary, the IEA reviewed published estimates that placed Bitcoin’s annual electricity use between 20 and 80 terawatt-hours (TWh). It also reported its own likely range of 10–20 million tonnes of carbon dioxide (Mt CO2) per year for Bitcoin mining, based on the analyses and operational data discussed at the time. These are historical estimates from 2019, not current figures. IEA, “Bitcoin energy use – mined the gap”.
Cambridge maintains a live Bitcoin electricity index, but a current numeric reading and date are necessary to report a present-day value responsibly. The 2019 figures should not be substituted for that reading. Cambridge Bitcoin electricity index.
Rank #3
Ethereum: a documented shift after The Merge
Ethereum.org reports annual electricity consumption of 2,601 megawatt-hours (MWh), or about 0.0026 TWh, and annual emissions of 870 tonnes of carbon dioxide equivalent (CO2e) for its proof-of-stake network. The figures cite research by the Crypto Carbon Ratings Institute (CCRI) and use regional carbon-intensity factors. Ethereum.org also reports CCRI’s estimate that the Merge, Ethereum’s transition from proof-of-work to proof-of-stake, reduced annualized electricity consumption by more than 99.988% compared with the prior PoW system. These are estimates with defined scope and methodology, not universal measurements for all blockchains. Ethereum.org’s energy-consumption documentation.
Ethereum.org says its estimates are based on publicly available data and are not an official statement or promise by Ethereum.org or the Ethereum Foundation. Cambridge has a separate Ethereum methodology, which is another reason to read each estimate in light of its own approach and boundaries. Cambridge’s Ethereum methodology.
Rank #4
How to compare blockchain climate estimates fairly
Before comparing two networks, check whether the figures describe the same period and cover the same parts of each system. A useful comparison asks:
- Consensus mechanism: Is the network using proof-of-work, proof-of-stake, or another approach?
- Electricity measure and period: Is the number an annual estimate, a live or moving-average estimate, or a one-time measurement?
- Emissions measure: Does it report CO2 or CO2e, and what electricity-use estimate underlies it?
- Geography and electricity mix: How does the method estimate where computing occurs and which energy sources supply it?
- Method and boundaries: What data and assumptions are included? Network electricity and emissions estimates do not, by themselves, constitute a full lifecycle comparison.
Cross-industry comparisons can be misleading when their boundaries and assumptions differ. Ethereum.org explicitly cautions about this, while Cambridge publishes distinct methodologies for Bitcoin and Ethereum. A ranking based only on one headline number can obscure what was counted and how the estimate was produced.
What can be concluded about blockchain and warming
Proof-of-work mining can drive substantial electricity demand, and the resulting emissions depend in part on the locations and electricity sources involved. Proof-of-stake can sharply reduce electricity demand, as Ethereum’s transition illustrates. But the estimates discussed here do not establish blockchain’s global climate impact relative to other sources of warming, nor do they provide a comprehensive lifecycle accounting across networks, including hardware manufacture and every indirect effect.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
