Clean NFTs is a phrase that a community of over 2000 artists from around the world use to describe NFTs from platforms offering Proof of Stake cryptocurrencies. In early 2021 a group of artists and members of the NFT community joined together on Discord to discuss the issues with Etheruem (Proof of Work) energy usage and since then have been working towards educating, raising awareness and looking at ways to improve the environmental impacts of releasing NFTs. 

General consensus;

• NFTs themselves do not produce carbon emissions 
• Ethereum currently has a carbon footprint associated with creating blocks by mining
• ETH is what the majority of NFT marketplaces use, which is currently transitioning to PoS, which is expected in 2021 or 2022
• NFT art platforms running on more energy efficient Proof-of-Stake (PoS) networks are currently the best solution for creating NFTs without impacting the environment with high energy use 
• There are now multiple NFT art platforms using PoS currencies
• Offering PoS options would be a great course of action for existing NFT art platforms to take
• Carbon offsetting has been discussed in great deal in the community and there are many different thoughts on this, best to make your own conclusions around effectiveness of offsetting