The Environmental Protection Agency's announcement Monday that it is going to regulate emissions that cause global warming has been expected ever since President Barack Obama took office.

The timing of the announcement sends a welcome signal at a crucial time. It comes as international momentum is building for the United States to take climate change seriously and lead to cut carbon emissions.

The EPA decision should bolster U.S. standing at the international climate change summit in Copenhagen, since other nations have justifiably accused one of the world's top two greenhouse-gas producers of dragging its feet on reducing its carbon footprint. (China is the other big polluter.)

It also will stir up a hornet's nest domestically, as industries facing new regulations gear up to challenge them in court. And it will reverberate on Capitol Hill, just as the administration intends. The House has passed legislation that would cut greenhouse-gas emissions by 17 percent by 2020 and about 80 percent by 2050 through a cap-and-trade program. A similar bill is languishing in the Senate, where it faces opposition from most Republicans and some Democrats.

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