Microsoft Co-Founder and billionaire Bill Gates dismissed cryptocurrency projects such as non-fungible tokens (NFTs) as shams “based on the greater-fool theory” at a climate conference on Tuesday (June 14), Bloomberg reported.

“Obviously, expensive digital images of monkeys are going to improve the world immensely,” Gates reportedly said sarcastically while speaking at an event in Berkeley, California hosted by TechCrunch. He said he’s neither long nor short the asset class, according to the report.

Gates has criticised crypto previously, sparring with Elon Musk last year over whether Bitcoin is too risky for retail investors and the environmental harm of mining coins.

Gates was speaking as the founder of Breakthrough Energy Ventures, the climate-focused fund he started in 2015. The billionaire also noted the difficulty of recruiting Silicon Valley engineers to work in industries like chemicals and steel production in need of lower greenhouse gas emissions.

Bitcoin slumped more than 15 percent on Monday and another 5.4 percent on Tuesday, part of a broader crypto sell-off fuelled by higher-than-forecast US inflation and the halt of withdrawals by crypto lending platform Celsius, according to Bloomberg.

Popular NFT collections, such as the celebrity-favoured Bored Ape Yacht Club, are also being hit hard.

ADDX is first Singapore financial institution to recognize crypto assets of accredited investors