Before The Merge, Ethereum was utilizing a Proof of Stake (PoS) mechanism which was extremely energy intensive. After The Merge which occurred on September 15th 2022, Ethereum switched to a Proof of Work (PoW) mechanism which was significantly less energy intensive, as it did not require a network of computers to be constantly mining to complete the next block on the underlying blockchain.
Details at Digiconomist here
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Interesting -- Apparently single Ethereum transaction footprints are now equivalent to the carbon footprint of 22 VISA transactions or 2 hours of watching YouTube.