Years before Congress began debating greenhouse-gas reduction, more than 500 U.S. cities had pledged to reduce their carbon footprints in line with the goals of the Kyoto Protocol. Now American cities are leading the way on adapting to climate change.

A growing body of research now confirms that the Montreal agreement averted at least one catastrophic form of climate change, even if others still loom. "The Montreal Protocol is a major success story," says William Randel.

Policymakers should focus on what needs to be achieved in the next 40 years in order to keep long-term options viable for avoiding dangerous levels of warming, a new study concludes.

In a vivid example of how a small geographic feature can have far-reaching impacts on climate, new research shows that water levels in the Bering Strait helped drive global climate patterns during ice age episodes dating back more than 100,000 years.

No matter how you slice it, the last few weeks have been consistently wintry across large chunks of North America and Eurasia.