With the American South thawing out after a deep freeze, you can be sure that plenty of the folks are interpreting the big chill as more proof that global warming is a hoax. "Warming?" they scoff. "How can the planet be warming when it's so darn cold?"

People in other parts of the world seem to have no great difficulty understanding the science, but in the good old USA, where quite a few people consider science just another political opinion, it is going to take a lot longer to get most people to accept the cold facts about a warmer world.

Put very simply, here is what the prevailing science says: Average global temperatures have been rising in recent decades. Some of the warming could be part of a natural cycle but, almost certainly, increased levels of CO2 in the atmosphere caused by the burning of fossil fuels are a pivotal factor in intensifying the phenomenon. The starkest evidence of the temperature jump is the rapid melting of the polar ice caps and the disappearance of the world's glaciers.

Climate scientists have said another key signal to watch for is a dramatic shift in weather patterns. It is close to impossible to attribute any single weather event -- a snowstorm, a tornado, a hurricane -- to temperature rise, but, once extreme weather becomes normal and what has been normal is no longer the norm, we will know we are in the throes of change that is likely irreversible.

It sure looks like that could be where we are now. In just the last couple of years, Americans have experienced epic tornados in the center of the country, a monster storm flooded Manhattan and ravaged New Jersey, extended drought in the West threatens agriculture and water supplies, and an unprecedented number of wildfires have consumed forests dried to the flammability of kindling. This winter, frigid polar air has slipped south, freezing much of the country while, in Alaska, the season has been unusually warm. There are piles of snow in Atlanta, but a dearth of snow in the Sierras.

Extreme and unusual weather has been rolling in with more frequency all over the world. Governments in most major countries have moved beyond debate about whether global warming is real. They are now busy making plans to deal with the costly disruptions and lethal disasters that climate change has already begun to bring.

Not in this major country, however. Though their nominee for president in 2008, Sen. John McCain, declared that all the things that need to be done to cope with and combat climate change would be worth doing even if warming were not happening, the dominant voices in the Republican Party sharply disagree. They seem fixated on loony conspiracy theories that imply that the scientists of the world are spinning lies in order to destroy American capitalism.

Spring will eventually come, but too many American minds will remain in a deep freeze of denial. And because so many of the deniers hold seats in Congress, climate change will stay on the growing list of daunting problems that our political system is unable to address.

Two-time Pulitzer Prize winner David Horsey is a political commentator for the Los Angeles Times. Go tolatimes.com/news/politics/topoftheticket/ to see more of his work.