Mining

Bitcoin uses a proof-of-work system or a proof-of-transaction to form a distributed timestamp server as a peer-to-peer network. This work is often called bitcoin mining. During mining, practically all of the computing power of the bitcoin network is used to solve cryptographic tasks, which is proof of work. Their purpose is to ensure that the generation of valid blocks involves a certain amount of effort so that subsequent modification of the blockchain, such as in the 51% attack scenario, can be practically ruled out.

Because of the difficulty, miners form "mining pools" to get payouts despite these high power requirements, costly hardware deployments, and hardware under control. As a result of the Chinese ban on bitcoin mining in 2021, the United States currently holds the largest share of bitcoin mining pools.^([needs update])

Requiring a proof of work to accept a new block to the blockchain was Satoshi Nakamoto's key innovation. The mining process involves identifying a block that, when hashed twice with SHA-256, yields a number smaller than the given difficulty target. While the average work required increases in inverse proportion to the difficulty target, a hash can always be verified by executing a single round of double SHA-256.

For the bitcoin timestamp network, a valid proof of work is found by incrementing a nonce until a value is found that gives the block's hash the required number of leading zero bits. Once the hashing has produced a valid result, the block cannot be changed without redoing the work. As later blocks are chained after it, the work to change the block would include redoing the work for each subsequent block. If there is a deviation in consensus then a blockchain fork can occur.

Difficulty and mining pools

Bitcoin mining is a competitive endeavor. An "arms race" has been observed through the various hashing technologies that have been used to mine bitcoins: basic central processing units (CPUs), high-end graphics processing units (GPUs), field-programmable gate arrays (FPGAs) and application-specific integrated circuits (ASICs) all have been used, each reducing the profitability of the less-specialized technology. Bitcoin-specific ASICs are now the primary method of mining bitcoin and have surpassed GPU speed by as much as 300-fold.

The difficulty of the mining process is periodically adjusted to the mining power active on the network. As bitcoins have become more difficult to mine, computer hardware manufacturing companies have seen an increase in sales of high-end ASIC products.

Computing power is often bundled together or "pooled" to reduce variance in miner income. Individual mining rigs often have to wait for long periods to confirm a block of transactions and receive payment. In a pool, all participating miners get paid every time a participating server solves a block. This payment depends on the amount of work an individual miner contributed to help find that block, and the payment system used by the pool.

Environmental effects

The environmental impact of bitcoin has been characterized in the literature as significant, particularly due to its energy use, greenhouse gas emissions, and electronic waste. Bitcoin mining, the process by which bitcoins are created and transactions are finalized, is energy-consuming and results in carbon emissions. According to the 2025 Cambridge Digital Mining Industry Report, surveyed miners reported that 48% of their electricity came from fossil fuels and 52% from sustainable energy sources, including renewables and nuclear.

Moreover, bitcoins are mined on specialized computer hardware that physically degrades through use, resulting in electronic waste. As of 2025^([update]), several empirical studies report an association between higher bitcoin-mining electricity use and worse environmental-sustainability indicators. Bitcoin's environmental impact has attracted the attention of regulators, leading to incentives or restrictions in various jurisdictions.

The OECD and the U.S. OSTP have discussed ways in which the environmental impact of crypto mining might be reduced, which includes grid balancing, use of otherwise-vented methane, and curtailed renewable electricity.