Bill Gatesis not a fan of cryptocurrencies or non-fungible tokens.

Speaking at aTechCrunch talkon climate change Tuesday, the billionaireMicrosoftco-founder described the phenomenon as something that’s “100% based on greater fool theory,” referring to the idea that overvalued assets will go up in price when there are enough investors willing to pay more for them.

Gates joked that “expensive digital images of monkeys” would “improve the world immensely,” referring to the much-hyped Bored Ape Yacht Club NFT collection.

NFTs are tokens that can’t be exchanged for one another. They’reoften touted as a way to prove ownership of digital assets like art or sports collectibles. But critics see them asoverhypedand potentially harmful to the environment given the power-hungry nature of cryptocurrencies. Many NFTs are built on the network behindethereum, the second-biggest token.

“I’m used to asset classes ... like a farm where they have output, or like a company where they make products,” Gates said.

As for crypto, “I’m not involved in that,” Gates added. “I’m not long or short any of those things.”

Cryptocurrencies tumbled sharply this week after Celsius, a crypto lending firm,paused all account withdrawals. The debacle has fueled fears of a looming insolvency event for Celsius — andpossible knock-on effectsfor other parts of the crypto market. For its part, Celsius says it’s “working around the clock for our community.”

The battered crypto world was already licking its wounds following the collapse of UST — a so-called “stablecoin” that was meant to be worth $1 — and luna, its sister token. At their height, both cryptocurrencies were worth a combined $60 billion.

Bitcoinwas last trading at $21,107 Wednesday, down 7% in the last 24 hours. The world’s biggest cryptocurrency has erased over half of its value since the start of 2022.