Nuclear power produces no greenhouse gases but raises issues of cost and waste disposal. John McCain wants to build 45 nuclear power plants by 2030.

By ANDREW C. REVKIN

Senator John McCain and Senator Barack Obama part company on many issues, but they agree that the Bush administration’s policies on global warming were far too weak.
Both candidates say that humancaused climate change is real and urgent, and that they would sharply diverge from President Bush’s course by proposing legislation requiring sharp cuts in greenhouse gas emissions by midcentury.
A high priority for Mr. McCain, of Arizona, is helping revive the nuclear- power industry because nuclear plants produce no greenhouse gases, once built. Mr. McCain wants to build 45 new plants by 2030, though experts raise questions about the cost and the storage of nuclear waste.
Mr. Obama, of Illinois, would create federal programs to cut energy waste and to encourage production of fuelsipping hybrids .
A top environmental goal of both candidates is enactment of climatechange legislation centered on a “cap and trade” mechanism that sets a ceiling on emissions that declines over time. Businesses and institutions that cannot hit the targets must buy permits from those that achieve bigger cuts than required.
The permits issued under Mr. Obama’s bill would be bought by businesses through an auction before they were traded. Mr. Obama says he would use some of the total auction revenue to help improve nonpolluting vehicles, wind and solar power, technology for capturing emissions from power plants, and other energy technologies. The brunt of the funds, he says, would help reduce costs faced by industries and citizens affected by the transition to a low-carbon economy.
Mr. McCain’s approach, according to his Web site, would distribute the permits initially at no cost, and move to auctioning “eventually.
Mr. McCain would also initially allow businesses to meet all their emission targets either directly or by buying a kind of credit, called an offset, generated by, say, a business that can prove an investment curbed carbon emissions that would otherwise have happened.
Environmentalists tend to prefer Mr. Obama’s approach.
Several representatives of industries said that, if forced, they would prefer the less aggressive targets and looser terms of Mr. McCain’s plan.
Without more details, it is not possible to estimate the costs of either candidate’s cap-and-trade plan, but economists generally agree that Mr. McCain’s would be less costly because of the offsets. But such offsets may also delay decreases in emissions.