Climate change deniers will have some explaining to do if the overwhelming consensus of climate scientists is correct about how human activity is dangerously warming our planet.

Of course, by the time the worst effects of climate change have destroyed coastlines, hobbled the global economy and upended the lives of millions, the loudest deniers of science will have shuffled off this realm. And in true Machiavellian form, those who are still around will likely protest that they were misunderstood, misquoted or misled by others.

A draft of the U.N. Intergovernmental Panel on Climate Change’s next report was obtained by several news outlets this week. Contained within are details and dire warnings:

“Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems.”

Let’s highlight just one word: “Irreversible.” That’s a long time for humans to contemplate why we didn’t act sooner.