It warped train tracks, melted the tarmac at Reagan National Airport and smashed thousands of daily temperature records across America. Last summer's brutal heat helped make 2012 the hottest year on record in the contiguous United States, federal experts said.
Climate change played a key role in that record, just as it has pushed up temperatures around the world. We've now experienced more than 330 months in a row of above-average temperatures.
That news puts President Barack Obama on the hot seat. As his second term begins, the president has a clear opportunity to revolutionize his whole approach to fighting manmade climate change. And 2012 couldn't have made a more powerful case for urgent action against the greenhouse gas pollution creating this problem.
Last year also bedeviled us with chaotic weather. Climate change is driving up the risk of extreme weather like devastating drought, and adding destructive power to storms like Superstorm Sandy.
America's future will be full of extreme heat, with growing risks of drought and food scarcity, according to the draft National Climate Assessment. Within decades, some states will suffer a doubling of days hotter than 95 degrees.
Our weather is also likely to become more destructive. Profound changes taking place in the Arctic are feeding North America's risk of extreme weather, in part by changing the jet stream.
Arctic sea-ice extent hit a record low last summer, and the region's snow cover has begun shrinking faster over the past decade.
Obama's Environmental Protection Agency could begin making full use of the Clean Air Act against greenhouse gas pollution. The EPA has begun applying the Clean Air Act to carbon-dioxide pollution, but progress has been modest.
We're running out of time to head off climate change's worst effects.
In his acceptance speech, Obama said, we want our children to live in an America that "that isn't threatened by the destructive power of a warming planet."
Those words must be matched by action, or we'll look back on 2012 as a year when we sped off the climate cliff.
Shaye Wolf is climate science director at the Center for Biological Diversity; email: swolfbiologicaldiversity.org.