By Edward Lotterman

We are fortunate that Sens. Amy Klobuchar, D-Minn., and Olympia Snowe, R-Maine, understand the importance of good measurement.

As the 19th-century British scientist Lord Kelvin pointed out, "When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind."

Without accurate information on the scope of problems, it is hard to implement effective solutions.

The senators introduced a bill this past week to establish a mandatory, uniform system of reporting greenhouse gas emissions. This is a useful bill. In itself, it will not reduce emission levels. But it would construct an indispensable baseline for any eventual "cap and trade" system that could help ameliorate climate change.

The fact that the two senators come from opposing parties is welcome. The issue of climate change is becoming sadly polarized. One wing, largely Democrats, portrays the problem in increasingly apocalyptic terms. Some on the other extreme describe climate change as a fraudulent hoax.

Republicans are split. Moderates like Arnold Schwarzenegger and Christine Todd Whitman advocate prompt government action. Others, typified by Oklahoma Rep. James Inhofe, continue to insist that "global warming is the greatest hoax ever perpetrated on the American people." A third group, including President Bush, is abandoning its assertion that warming is only a tenuous hypothesis, but persists in the vain hope that voluntary changes will render government action unnecessary.

Sens. Snowe and Klobuchar are both pragmatic centrists on environmental issues. Their bill is limited in scope. Currently, reporting of greenhouse gas emissions falls under a number of different EPA programs. It is largely voluntary and the criteria and reporting formats are not consistent. The resulting data "is of a meager and unsatisfactory kind."

The senators' "carbon counter" bill will solve that. It will not impose an undue burden on emitters. By establishing baseline data, it will facilitate planning by the many companies, including Xcel Energy, that are ahead of the Bush administration in recognition of the need for action.

Reducing emissions of carbon dioxide and other greenhouse gases follows the usual pattern of diminishing returns. Initial reductions can be cheap. Indeed, some are essentially free, in that more effective measures to reduce other pollutants would also reduce carbon emissions.

After such easy gains, further reductions become progressively more costly. To minimize costs to society, it is imperative to choose effective policies. Broad-based taxes on emissions probably are the cheapest first step. "Cap and trade" or "ratchet down and trade" systems for major emitters like power plants are the next most effective move. This bill moves along the right path.

St. Paul economist and writer Edward Lotterman can be reached at