One of the key features of the Shanghai upgrade is the implementation of the Proof-of-Stake (PoS) consensus mechanism. Currently, Ethereum uses a Proof-of-Work (PoW) mechanism, which is resource-intensive and requires a lot of energy to maintain. PoS, on the other hand, is more energy-efficient and less resource-intensive, making it a more sustainable option. This switch is expected to significantly reduce the carbon footprint of Ethereum.