As the ice melted, the issue gelled.
This was the year that global warming hit the mass radar screen, driven by a drumbeat of catastrophic predictions from top scientists, a jaw-dropping acceleration in polar ice melt, Al Gore's Oscar - and then his Nobel.
His prize showed how important the issue was. His cameo on NBC's 30 Rock showed how mainstream it was.
As recently as 2003, when climatologist Heidi Cullen began her 90-second spots on the Weather Channel, global warming seemed fringe.
Now, her program is an hour, and global warming is a dinner-table topic coast to coast. "It's found its way into basic American dialogue," Cullen says.
When sea-level researcher Benjamin Horton talked climate change in 2006, his University of Pennsylvania students yawned.
This year, same class, seismically different evaluations. They "think it is the most important thing for science to understand," Horton says.
Indeed, researchers say, most Americans now understand the potential of global warming to affect every facet of society: energy production and use, population growth, water resources, storms, droughts, human health.
Few missed the import of the Nobel. It was the peace prize, a nod to fears of famine, environmental refugees and wars over water and other resources.
In years to come, climate change seems certain to alter America's very way of life - the houses people live in, the cars they drive.
This was the year world communities came together to debate the problem.
Washington vacillated - but states acted, often led by California's example.
Unlikely bedfellows - eco groups and corporations like DuPont, Dow and Ford - formed a climate partnership to demand government action.
Religious leaders ratcheted up the rhetoric.
Six hundred stalwarts stood naked on a glacier in the Swiss Alps.
And us? The gas-guzzling, thermostat-wielding public?
We bought energy-saving compact fluorescent lightbulbs - enough that Wal-Mart reached its year-end sales goal of 100 million by Oct. 2.
Some even took public transit to the Live Earth concerts on climate change.
"It was a cover story everywhere," says Greenpeace research director Kert Davies. "It was in your lap, in the dentist's office, on local news."
Attitudes continued a shift seemingly as inexorable as climate change itself.
According to a new GlobeScan poll, 65 percent of Americans believe climate change will directly threaten them and their families.
