Move over, coal plants. The new targets in the campaign against carbon pollution are the tailpipes of our cars and trucks.

When Minnesota legislators open their new session next week, they will be greeted with a bill that proposes to assign petroleum producers and refiners a new responsibility in the campaign to reduce greenhouse gases. Much as automakers are expected to build ever-more-efficient cars, the petroleum industry would be expected to produce ever-cleaner fuel -- specifically, 10 percent cleaner over the next 10 years.

The bill's backers say it would expand government controls beyond those already proposed for the energy sector, the nation's biggest source of carbon emissions, to the transportation sector, the second leading source of such emissions in Minnesota and in most other states.

In California, where transportation accounts for 40 percent of carbon emissions, the nation's first "low-carbon fuel policy" was established last year. Now, Minnesota, Massachusetts and Florida are seeking to follow suit with policies that would require a 10 percent reduction in the carbon content of all passenger vehicle fuels over 10 years.

The policies have their critics, including the American Petroleum Industry, that call them unworkable and unfair. But supporters see them as inevitable, in one form or another, as the movement toward clean and renewable energy spreads across the states.

"In Minnesota, the energy sector is responsible for about a third of our carbon emissions, and the next biggest chunk, about 25 percent, comes from transportation," said Bill Grant, Midwest director of the Izaak Walton League in St. Paul. "So if you do the math, and you look at the very aggressive goals we're trying to meet, you can't ignore the two largest sources of those emissions."

Complicated mechanism

The system put in place by the policies is so complicated that California expects to be working out the details well into this year. But generally they would rate every possible vehicle fuel -- including gasoline, ethanol, electricity and eventually hydrogen -- according to carbon content. And every producer and refiner of those fuels will be given one carbon cap each year for all its fuels combined. Over 10 years, each cap will drop by 10 percent.

Producers can meet their goals in many ways, Grant said. A refinery that currently produces only straight gasoline can start to make gasoline-ethanol blends, for example. Another could use more biomass and less corn in ethanol blends that it's already producing.

The legislation, whose chief sponsors are Rep. Melissa Hortman, DFL-Brooklyn Park, and Sen. Kathy Sheran, DFL-Mankato, would rely on data from the Argonne National Laboratory, a U.S. Department of Energy research center, to calculate the carbon number for each energy source.

But the biggest controversy springs from the policies' starting premise, which is to rate each fuel based on all the carbon that gets used from its beginnings to its burning -- its "life cycle," said Brendan Jordan at the Great Plains Institute in Minneapolis, a research group that promotes the use of renewable energy.

Ethanol's rating, for example, would begin with the diesel in the tractor that planted the corn that was used to make the ethanol. Gasoline's "well-to-wheels" total will include whatever fueled the tanker that carried the crude across the ocean.

The energy industry says it's a bad time to consider such measures. Because it would raise energy prices, it's the last thing this troubled economy needs, said Erin Roth, a director in Wisconsin of the American Petroleum Institute.

There also is fundamental disagreement concerning the policies' value. Kenneth Green, a resident scholar in climate policy at the American Enterprise Institute in Washington, considers them a distraction from the search for revolutionary technology 15 to 20 years out that can cool the planet or pull carbon out of its water, for example.

"We need to be investing in research that looks for something on a scale that will help," he said.

But at the Izaak Walton League, Grant said he's convinced that the policies will be a needed incentive. "We need a market signal to begin weaning ourselves from fossil fuels at last," he said.

H.J. Cummins • 612-673-4671