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Some experts worry we may be approaching a "tipping point" of global warming, beyond which we won't be able to return to our familiar climate. (MPR Photo/Stephanie Hemphill)

So far it's been another one of those "winters that wasn't." Not just in Minnesota, but the whole Earth has just lived through the warmest year on record. When you think about our warm temperatures, and Hurricane Katrina, you might wonder -- is all this proof of global warming? Experts say there's growing concern.

Duluth, Minn. — January in Minnesota was the warmest since modern records have been kept, more than 100 years.

But University of Minnesota climatologist Mark Seeley says one wimpy winter can't prove the climate is changing. He says there have been other warm Januarys, even strings of warm winters.

"The climate change community likes to tend to hang their hat on longer term trends," he says. "That is, measurements and patterns that are certainly of longer duration, and particularly those that fall outside the range of historical variability."

Seeley says there is evidence of global warming, lots of places on Earth. He's studied the work of a Penn State researcher named Michael Mann.

Mann uses tree rings, ice cores, and other ways to figure out how the climate has changed over the last one thousand years. Seeley says Mann draws a temperature graph that looks like a hockey stick.

"That is, the first 900-plus years form a handle, if you laid a hockey stick on its side, and the last hundred years or so forms the blade," Seeley says.

He says Mann's diagram shows how sharply temperatures have risen since the beginning of the industrial age.

Most scientists agree, human activity has dramatically increased carbon dioxide and other chemicals that trap heat in the atmosphere.

Peter Ciborowski is the climate change expert at the Minnesota Pollution Control Agency. He says there's a lot of evidence the climate has changed already - especially near the North Pole.

"You're seeing dramatic decreases in Arctic ice, you're seeing permafrost melt, you're seeing bushes grow where bushes don't grow, you're seeing mosquitoes and robins -- many quite peculiar things," he says. "It's moving very fast; it has many scientists quite concerned."

Some scientists say we're approaching a tipping point, where the changes could become irreversible, and we won't be able to go back to the climate we're used to. Ciborowski compares it to a fast drive on a dangerous road.

"You've got your foot down on pedal, you're going 90 miles an hour," he says. "You get very concerned that you're not going to be able to control the car; you're coming into terrain you don't know; maybe the weather conditions aren't right. The sensible thing is to slowly ease your foot off the gas pedal, until you have a better sense that in fact you're going to be able to survive the drive."

Ciborowski says we need to use less fossil fuel, and use it more efficiently. For instance, he says, we could all drive cars with far better gas mileage. Like 50 or 60 miles per gallon.

"If everyone were to do that, we could reduce our emissions of greenhouse gases from transportation by in the order of two-thirds," he says, "and do it over maybe a ten year period."

In his state of the union address, President Bush called for a billion-dollar investment in hydrogen-powered cars. He wants the clean technology to be on the road a generation from now.

Others want faster action.

Last year Senators McCain and Lieberman sponsored a bill called the Climate Stewardship Act. It failed to pass, but it will likely be brought up again. It would put a cap on emissions of carbon dioxide and other greenhouse gases, and allow companies to trade their emission permits. Michael Noble is with ME-3 -- Minnesotans for an Energy Efficient Economy. He says that approach would stimulate innovation.

"You know, the energy use is growing," he says. "And by putting a limit on fossil fuel pollution, we both strengthen our economy, we actually improve our defense issue by reducing our reliance on foreign oil, and we help the environment all at the same time."

Noble says other countries are encouraging new technologies because they're committed to greenhouse gas reductions in the Kyoto treaty. He says American companies will have to play catch-up.

Noble and other environmentalists will push during the next legislative session for a state law requiring Minnesota utilities to generate 25 percent of their electricity from renewable sources by 2020.