In late March, when the United States and China jointly declared that they’d be moving to immediately sign and then join the Paris climate agreement “as early as possible this year,” it was seen as the latest show of joint leadership by the two largest emitters.

But there’s another possible implication that went largely unnoticed. If the nations of the world, led by its two biggest contributors to climate change, jump through all the hoops needed to bring this agreement into force before President Obama leaves office, the next U.S. president could have a difficult time — or at least, a long wait — if he or she wanted to get out of it.

The Paris agreement does not state or limit when it can go into effect — it simply depends on when enough countries formally sign and join it. If that occurred while Obama is still in office, “then the next president could not withdraw until sometime in 2019, and the withdrawal would not be effective until sometime in 2020,” said Daniel Bodansky, a scholar of international environmental law at Arizona State University and a former attorney at the State Department focused on climate change.