How much warming will greenhouse gas emissions cause in the coming years? It’s one of the most fundamental questions about climate change — and also one of the trickiest to answer.

Now, a major study claims to have narrowed down the range of possible estimates.

It presents both good and bad news. The worst-case climate scenarios may be somewhat less likely than previous studies suggested. But the best-case climate scenarios — those assuming the least amount of warming — are almost certainly not going to happen.

It’s “the most important climate science paper that’s come out in several years,” according to climate scientist Andrew Dessler of Texas A&M University, who was not involved with the study.