This image made available by the National Oceanic and Atmospheric Administration on December 17, 2015 shows warmer- or cooler-than-normal temperatures around the world for January through November 2015. If governments are serious about the global warming targets they adopted in Paris, scientists say they have two options: eliminating fossil fuels immediately or finding ways to undo their damage to the climate system in the future. The first is politically impossible — the world is still hooked on using oil, coal and natural gas — which leaves the option of a major clean-up of the atmosphere later this century.