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Blockchain does not have one fixed climate footprint. The impact depends chiefly on how a network reaches agreement: proof-of-work systems such as Bitcoin use electricity-intensive mining, while proof-of-stake systems such as Ethereum use a different process that can require substantially less electricity. Electricity use alone is not the same as greenhouse-gas emissions; those also depend on where the computing takes place and how that region generates power.
How blockchain can contribute to global warming
A blockchain network maintains a shared record of transactions through computers that follow a consensus mechanism. In proof-of-work (PoW), miners compete using computing power to validate transactions and add blocks. The International Energy Agency describes the resulting energy use as both a security feature and a side effect of that competition. IEA: Bitcoin energy use – mined the gap.
When electricity is generated using fossil fuels, the electricity consumed by mining can result in greenhouse-gas emissions that contribute to warming. But the relationship is not one-to-one: the same electricity demand can have different emissions depending on the location and electricity mix. A network’s estimated climate impact therefore requires more than an electricity-use figure.
Why electricity use and emissions are different measures
Electricity consumption measures energy used over a period. Emissions estimates depend on that consumption plus assumptions or data about where miners operate and the emissions intensity of their electricity. Cambridge Centre for Alternative Finance explains these elements in its Bitcoin GHG emissions methodology, which derives emissions estimates from consumption and mining-location data.
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Estimates also depend on their timeframe and method. Cambridge uses a seven-day moving average in its Bitcoin index to reduce the effect of short-term hashrate volatility. Its live index should be consulted for a current value; a figure reported for a different date or calculated using another method is not a like-for-like substitute. The IEA’s estimates below are historical, not current readings.
What the available figures show
| Network or estimate | Electricity use | Emissions | Scope and date |
|---|---|---|---|
| Bitcoin estimates reviewed by the IEA | 20–80 TWh per year | 10–20 Mt CO2 per year | Ranges reported by the IEA in 2019, reflecting estimates and operational data available at that time; not current values. IEA, 2019. |
| Ethereum proof-of-stake | 2,601 MWh per year (0.0026 TWh) | 870 tonnes CO2e per year | Ethereum.org documentation, accessed October 7, 2026, citing CCRI research. The emissions estimate uses regional carbon-intensity factors. Ethereum energy consumption. |
The figures are not a controlled comparison: they refer to different networks, sources, and periods. The IEA values describe Bitcoin estimates reported in 2019, while the Ethereum figures are estimates for Ethereum’s proof-of-stake network based on CCRI research. They should not be read as current Bitcoin-versus-Ethereum measurements made under a single shared methodology.
How Ethereum’s move to proof-of-stake changed its energy use
Ethereum’s transition from proof-of-work to proof-of-stake, known as The Merge, changed the mechanism used to secure the network. Ethereum.org reports CCRI’s estimate that annualized electricity consumption fell by more than 99.988% after the change. This illustrates how changing consensus can alter a particular network’s electricity demand; it does not establish the footprint of every proof-of-stake chain or every blockchain use.
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Ethereum.org says its figures are based on publicly available data and are not an official statement or promise by Ethereum.org or the Ethereum Foundation. Its documentation also references a Cambridge index that uses a different method. For details on the network-specific approach, see Cambridge’s Ethereum methodology.
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How to compare blockchain climate claims
Before comparing two networks or repeating a headline statistic, check whether the numbers refer to the same kind of measurement and timeframe. A useful comparison should identify:
- Consensus mechanism: for example, proof-of-work or proof-of-stake.
- Electricity measure and period: annual use, a dated estimate, or an annualized figure based on a shorter observation window.
- Emissions measure: such as CO2 or CO2e, and whether it is an estimate or a reported measurement.
- Geography and power mix: where the network’s computing occurs and what electricity sources are assumed.
- Method and system boundary: what the estimate includes, what data it uses, and what limitations its authors disclose.
These checks matter because electricity and emissions methods can differ, and comparisons across sectors may use different boundaries. Ethereum.org specifically cautions readers about cross-industry comparisons; Cambridge publishes separate methodologies for Bitcoin and Ethereum.
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What these estimates do not establish
The figures here concern network electricity use and related emissions estimates. They do not provide a comprehensive lifecycle comparison across blockchain systems, including hardware manufacturing and every indirect effect. Nor do they, by themselves, establish that blockchain’s contribution is globally material compared with other causes of warming. Such a conclusion would require broader comparisons using consistent dates, scopes, and methods.
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