A fifth myth about blockchain is that it is green, meaning that it is environmentally friendly or sustainable. This is also not entirely true, as there are environmental impacts and costs associated with the operation and maintenance of different blockchains. Some blockchains are more energy-intensive than others, depending on the consensus mechanism, the hardware, the network size, and the incentives. For example, blockchains that use proof-of-work, such as Bitcoin or Ethereum, require a lot of computing power and electricity to secure and validate the transactions, which generates a lot of carbon emissions and waste. Blockchains that use proof-of-stake, such as Cardano or Polkadot, require less computing power and electricity, but still have some environmental footprint. Blockchain proponents and critics often debate on the energy efficiency and sustainability of blockchains, by comparing them to other systems or sectors, such as banking, gold, or internet.