WASHINGTON -- Energy Secretary Steven Chu yesterday laid out the scientific risks of inaction on global warming and then went straight to his main point: The climate and energy bill starting its way through the Senate could help drive what he called "energy opportunity."

The Senate is only now taking up the bill -- yesterday was its first hearing -- and much could change as senators demand amendments and compromises. No Republicans now support it, though Sen. Lindsey Graham, R-S.C., has written that he is interested in a consensus approach.

The bill's Democratic supporters are looking for some GOP allies to help secure the 60 votes needed to overcome procedural blocks for passage. They are also working against the odds to get the bill finished in time for international climate negotiations in December in Copenhagen, Denmark. The House passed a version in June, but before anything is enacted into law, the House and Senate must agree on identical terms.

Mr. Chu, leading off testimony before the Senate Environment Committee, noted that a Massachusetts Institute of Technology study this year found a 50 percent chance of a 9-degree Fahrenheit temperature increase in this century, and a 17 percent chance of a nearly 11-degree increase if heavy dependence on fossil fuels continues. Those numbers are higher than a 2007 international scientific consensus report, which estimated an increase of more than 7 degrees.

"The world now realizes that its current level of greenhouse gas emissions is unsustainable," Mr. Chu said. Demand for clean-energy technologies will leap as countries strive to limit emissions, he said.

"The only question is: Which countries will invent, manufacture and export these clean technologies, and which countries will become dependent on foreign products?" Mr. Chu said the climate-change legislation was needed to help the United States catch up with China, Denmark and Japan.

"The most important element of this bill is that it puts a cap on carbon emissions that ratchets down over time," he said. "That critical step will drive investment decisions toward clean energy."

The Senate bill would reduce U.S. emissions by 83 percent from 2005 levels by 2050. The Environmental Protection Agency concluded that this reduction would put the United States in line with international efforts to limit climate change.

The Senate bill is similar to the one the House passed in June. It would require sources of 25,000 tons or more of heat-trapping gases a year, roughly the output of 2,300 homes, to buy permits to release them. Companies that found cleaner approaches would need to buy fewer permits and could sell those they didn't need. The bill would require payment only from these large sources, which produce 75 percent of U.S. greenhouse gases.

Investments in power plants require billions of dollars. A requirement to reduce greenhouse emissions from coal would make nuclear, wind and solar power more attractive, Mr. Chu said.

Republicans on the panel opposed the mandatory emissions reductions and said they preferred conservation, nuclear energy and encouragement of electric vehicles and other cleaner technology. They also argued that the bill would cost too much and cost jobs.

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