The past year has seen an explosion in the number of companies announcing they are now “net-zero” or “carbon neutral,” or at least plan to be in the next 30 years. Unilever, Uber, and Facebook are just a few of the recent additions to the club, and even major oil companies like BP and Shell say they are on board. If you’re rolling your eyes and thinking this is just the latest PR stunt, you’re not wrong — if you read the fine print, companies have defined those terms for themselves in a number of different, and often not very meaningful, ways. But you’re also not entirely right, because “net-zero” is more specific than “sustainable” or “eco-friendly.” It’s measurable, at least in theory. Here are 4 ways to tell whether a company’s climate pledge is legit.