The science revealing rising risks of disruptive human-driven climate change has accumulated like dots added to a pointillist painting, but the resulting image still lacks clarity. The result is one of the great paradoxes of the early 21st century: a potential planet-scale threat that perpetually hides in plain sight. Parts of the climate picture are visible now in high resolution. There is no longer any reasonable way to explain recent changes in atmospheric and ocean temperatures without a substantial contribution from accumulating human-generated greenhouse gases. Arctic sea ice in summer is dwindling. Tropical climate conditions are expanding. The stratosphere is cooling, as predicted, while lower atmospheric layers warm.
For many of the most consequential climate impacts, though, the picture remains fuzzy. Rising sea levels are certain in a warming world, but there is still substantial uncertainty about the extent of the increase in this century, mainly because the dynamics that ...
