Bitcoin, by a wide margin: on its own it accounts for more than 95% of the greenhouse gas emissions of the whole crypto market. The reason is its consensus mechanism, Proof of Work, which relies on a very energy-intensive race for computing power. Ethereum, Solana, Cardano and Polygon run on Proof of Stake, which uses tens of thousands of times less energy; others, such as Litecoin and Dogecoin, remain on Proof of Work.
Read the source article: Bitcoin carbon footprint: 33 tCO2e/year per million euros held