The U.N. climate chief says world leaders must recognize there is no option except to speed-up and scale-up action to tackle global warming, warning that continuing on the current path will lead to "a catastrophe."

Patricia Espinosa stressed in two recent interviews with the Associated Press that climate scientists say there's still a chance to make things right "but the window of opportunity is closing very soon" and the world has 12 years until carbon emissions reach "a point of no return" — something some top scientists say is an oversimplification of a U.N. report last year.

She said that means the world needs to accelerate all efforts to keep from reaching that level, "and therefore all efforts are absolutely indispensable" to cut carbon emissions and keep temperatures from rising.