On stage at TC Sessions: Climate 2022 this week, renowned climate modeling expert Dr. William Collins shared why he’s deeply skeptical of carbon offsets, and tree-based offsets in particular.

Asked whether offsets serve as a “get-out-of-jail-free card” for companies eager to show they care about the climate, Collins replied that offsets are, “as far as we can tell, a feel-good measure.” Tree-planting programs pedestalized by companies such as United Airlines are “fool’s gold,” Collins said. “It’s essentially impossible to monitor whether or not the stuff is going to stay in the trees. The minute you have a forest fire — game over,” he added.

You might be bummed to hear that from Collins, who directs Berkeley Lab’s Climate and Ecosystem Sciences Division and Carbon Negative Initiative. Collins also served as a lead author of several IPCC assessments, one of which won a Nobel Peace Prize in 2007.

To be clear, forest preservation is critical, especially when such efforts are led by indigenous communities instead of colonialistic governments and corporations. However, the track records of creditized forest preservation and mass-planting initiatives are a different story. A 2019 ProPublica investigation found that “carbon credits for forest preservation” in particular “may be worse than nothing,” echoing Collins’ concerns.

Along similar lines, Collins also pointed to forest-preservation pledges that were baked into the Paris Agreement: “A third of the countries in the Paris accord are essentially saying, ‘we won’t cut down our forests [and that] is our primary contribution to greening the planet.’” Yet, per Collins it’s entirely unclear what material gains these pledges offer in terms of carbon sequestration.

“The estimates that they have given for how much [carbon] their forests hold vary by factors of four across country boundaries,” said Collins. He added, brutally: “that tells you that they’re making the numbers up.” On top of that, some groups argue there isn’t enough space for all the trees that corporations aspire to plant, anyways.

Beyond trees, Collins did not go into great detail on other types of carbon offset programs, such as those that turn biomass into oil for underground storage and atmospheric carbon removal credits. Regarding the latter, Salesforce, Microsoft and Google recently pledged to put $500 million towards atmospheric carbon removal, even though such tech is currently unproven at scale.