In recent weeks several organizations have started experimenting with non-fungible tokens (NFTs) on top of the Polygon network. Associated press announced it was launching an NFT marketplace on top of Polygon, while also Prada, Adidas and the World Wildlife Fund (WWF) launched their own NFT projects using Polygon. These decisions immediately faced backlash from environmentalists concerned with the sustainability of NFTs. NFTs have become highly controversial due to their significant carbon footprints, as most of them are minted on top of the Ethereum network. Just like Bitcoin, Ethereum currently makes of the energy intensive proof of work mechanism to run its underlying blockchain technology. As a result, the Ethereum network is already responsible for consuming as much electrical energy as up to half of our total global data center energy usage (excluding cryptocurrency mining facilities), with a total carbon footprint equivalent to the size of Sweden’s total footprint. This footprint automatically reflects in anything that is built on top of the Ethereum network, which is why NFTs built on top of the Ethereum network can have substantial carbon footprints as well.
Organizations like the WWF are aware of this, which is why they have opted to use the “eco-friendly” Polygon network. The latter uses proof of stake, which can tremendously reduce the amount of energy required to run the underlying blockchain. Based on 100 validators taking part in Polygon’s proof of stake network, the WWF concluded “each transaction on Polygon produces just 0.206587559 grams CO2,” which is a long way from the 124.34 kilograms of CO2 per transaction on the Ethereum network. The WWF therefore establishes that there is a “limited environmental impact of minting NFTs on Polygon.” This conclusion would be accurate if Polygon operated independently of the Ethereum, but this is not the case. In fact, Polygon operates a set of contracts on the main Ethereum network that facilitate essential services such as moving assets between Ethereum and Polygon and creating checkpoints. A full lists of relevant contracts built on Ethereum, operated by Polygon, can easily be found using a blockchain explorer like Etherscan.
As these contracts are required for Polygon to function, their carbon footprint should be included when considering Polygon’s total carbon footprint. We can establish the carbon footprints of these contracts in the same way we would assess the carbon footprint of any NFT collection built directly on top of the Ethereum network, by proportionally allocating emissions based on the share of gas used to run the contract (in Ethereum gas is required to interact with the network).
On February 3, 2022, the contracts “Matic Token”, “Bridge”, “Plasma Bridge” and “Root Chain Proxy” used a combined amount of 1.1 billion gas. On the same day 99.2 billion gas was used in total on the Ethereum network. This means that at least 1.1% of all gas used on Ethereum was related to Polygon. With the carbon footprint of Ethereum amounting to 144,712,329 kilograms of CO2 on February 3, we can allocate 1,598,215 kilograms of CO2 to Polygon for this day. Since we can also find that Polygon processed 3,718,755 transactions on February 3, we can establish the carbon footprint of a Polygon transaction is close to 430 grams of CO2. This is almost 2,100 times more than the optimistic estimate provided by the WWF, illustrating that Polygon is nowhere near as sustainable as claimed.
Because of the controversy regarding their experiment, the WWF halted the NFT trial shortly after launching it. Similar scenarios may be avoided by carefully evaluating the design of a chosen platform. Even though Polygon still depends on Ethereum to function, there are plenty of other alternatives that make use of proof of stake in an independent setup.