Washington ? As Congress begins to debate climate change in earnest, the science is taking a back seat to economics: How much will it cost to slow the Earth’s warming because of man-made pollution — and what’s the cost of doing nothing?

With a key House committee starting four days of hearings, Speaker Nancy Pelosi, D-Calif., vowed to get a climate bill approved this year. Noting that Earth Day will be celebrated today, she told reporters by the next Earth Day “we want to celebrate what we’ve done this year” to address climate change and clean energy.

But the challenge of getting bipartisan support immediately became apparent.

The Energy and Commerce Committee hearing had barely begun when Republicans raised their concerns about higher energy prices produced by putting an added price for burning fossil fuels.

“In its current form, this bill may do more harm to our economy than any bill that is likely to come before Congress for the rest of this year, or perhaps during my natural lifetime,” declared Rep. Michael C. Burgess, R-Texas.

Rep. John Dingell, D-Mich., whose state’s already is reeling economically and home to energy-intensive industries, said the economic impact of the bill drafted by Democrats “cannot be overstated” unless ways are found to blunt expected increases in energy costs.

The Democratic proposal calls for broad limits on carbon dioxide and other greenhouse gas emissions, meaning energy from fossil fuels, especially coal in the production of electricity, will become more expensive. It would cut greenhouse gases by 20 percent from 2005 levels by 2020, and 83 percent by mid-century.

The bill also includes a string of measures aimed at reducing the use of fossil energy such as requiring utilities to produce a quarter of their electricity from renewable sources, and calling for tougher standards to promote energy efficiency.

The proposed “cap-and-trade” system would limit greenhouse gas emissions and allow industries to buy and sell emissions credits in the open market to make it easier, and less expensive, to comply with the emissions ceiling.

A key question yet to be resolved is how the government should make available pollution permits: Sell all at an auction or provide them for free to industries most greatly affected such as coal-burning power plants and energy intensive industries.

“We need to talk that through with our members,” said Committee Chairman Henry Waxman, D-Calif., who said he’s confident “it will be resolved in the legislative process.”