The Nobel is an acknowledgment that Gore was right about the greatest global threat we face.

From TIME:

This Prize, after all, is a recognition that Gore has done more than anyone else (excepting Mother Nature) to bring about a sea change in public opinion. An overwhelming majority of Americans — 90% of Democrats, 80% of independents, 60% of Republicans — now say they favor "immediate action" to confront the climate crisis. Gore helped make that happen, but he can't take too much satisfaction in it. As he [said] last spring, "Time is running out, and we still haven't done anything."