Why NFTs at Highrise are Carbon Neutral

Pocket Worlds
Published in
4 min readJan 5, 2022


Proof-of-Work Blockchains like Bitcoin and Ethereum have received much criticism about their carbon footprint. As a nascent technology, blockchains are quickly evolving to improve and solve inefficiencies that can have negative environmental consequences.

This is why Highrise’s blockchain efforts have been developed on Immutable X — a blockchain whose intended purpose is much greater efficiency, and thus a neutral effect on carbon emission.

But first… what are NFTs?

NFTs, or non-fungible tokens, are special types of cryptographic tokens that represent assets covering a wide range of unique tangible and intangible items. These assets include collectible trading card NFTs (e.g. Gods Unchained), digital art (e.g. popularized by Beeple and Pranksy), virtual worlds (e.g. Highrise), and even digital sneakers (e.g. RTFKT Studios). NFTs can be created (AKA minted), traded, earned, shared, gamed, and collected — and this can happen on marketplaces, on exchanges, or in games. NFTs are interoperable. Digital goods now have real value to users in the form of free-market economies and secondary markets.‍

Some of you may have heard the term gas fees. These fees are the cost of using the Ethereum network. Gas fees are payments made by end-users or applications on Ethereum to compensate miners for the work required to process and validate transactions on the Ethereum blockchain. Ethereum gas fees fluctuate with demand and have risen sharply, presenting persistent issues that make trading NFTs in a marketplace more expensive for users per trade. Importantly, Ethereum always uses the same carbon footprint in the short run: your NFT has the same environmental impact irrespective of the gas fee it uses (so lowering it doesn’t help!).‍

Immutable X has created the first carbon-neutral scaling solution for NFTs on Ethereum.

Immutable X is a Layer 2 blockchain. Layer 2 chains refer to a popular method of scaling Ethereum while still retaining its security. Some L2s aim at fixing one or more scalability issues within the Ethereum blockchain. Immutable has built a dedicated L2 solution for scaling NFTs on Ethereum called Immutable X (an “exchange protocol”). Immutable X provides transaction scalability (up to 9,000 transactions per second), gas-free NFT trades and creations, and is fundamentally decentralized by relying on Ethereum — as opposed to a sidechain.‍

Any NFT that is created or traded on Immutable X is 100% carbon neutral.‍

Immutable X lowers energy consumption 475,000x

Fundamentally, Immutable X scales Ethereum by taking up less of the network per NFT mint or trade — while still retaining its security. Normally, NFT trades or mints occur directly on Ethereum. Immutable instead uses zero-knowledge proofs to have those Ethereum keys sign transactions, and these transactions are then batched into a compressed validity proof and uploaded to Ethereum. Less gas = less energy used = less carbon.

Immutable X compresses the amount of information required to trade or create an NFT secured by Ethereum via batched zero-knowledge proofs. To illustrate this concept with an example: historically, minting 8 million Gods Unchained cards (the NFT trading card game) on Ethereum would consume approximately 490 million kWh (490 mWh).

On Immutable X, Gods Unchained minted 8 million NFT cards with only ~1,030kWh = 844 kg CO2. That’s 475,000 times less energy consumption.

To put this in perspective a one-way flight from LAX to NYC is 807 kWh = 662 kg CO2. These numbers are comparable to minting the cards using a centralized database.

Immutable offsets the carbon footprint to zero

Immutable buys carbon credits needed to offset the energy footprint of any NFT created or traded on Immutable X to zero. That means:‍

  • Any NFT that is created or traded on Immutable X is 100% carbon neutral.
  • Any NFT marketplace that is built on Immutable X is 100% carbon neutral.
  • Any NFT game that is built on Immutable X is 100% carbon neutral.‍

Immutable committed to covering the ongoing cost of carbon credits into at least 2025, which means they will cover any carbon impact of Highrise NFTs.

Like Immutable, we don’t want ecological unsustainability to stop the greatest shift in monetization power from incumbents to content creators the world has seen. We share Immutable’s vision in shifting the power dynamic to developers, artists, creators, collectors, traders — all while power consumption dramatically decreases.


[1] Measuring carbon emissions on the Ethereum blockchain requires some complicated maths and depends on many factors. Immutable took a top-down approach starting with the total energy consumption of Ethereum in a year, then calculated the percentage of Ethereum blocks Immutable X will consume. Immutable’s consumption estimate was uploading one Validium zero-knowledge proof to Layer 1 every hour. Finally, Immutable converted the energy consumption to carbon emissions based on the energy being produced in the United States.

[2] This is a similar calculation Immutable adapted for Validium to measure kgCO2 as measured by Digiconomist and Memo Atken.

[3] On a macro level, accelerating the trading and collecting of digital NFTs offsets the need for environmentally wasteful throwaway physical goods. Reducing the physical reproduction of certain physical goods (e.g. fast fashion, music, plastic games) and moving to more digital collection options like NFTs will reduce global carbon emissions. Namely, it will reduce mineral mining for plastics, production, supply chain, and transport pollution. Transport had the largest impact on energy consumption at 8,265 TWh in the US in 2019.