Compare candidates' stands on climate change

Barack Obama and John McCain agree the U.S. can't keep pumping greenhouse gases into the atmosphere unchecked, because their accumulation threatens to bring rising seas, mass extinction of plants and animals, and more hunger, disease and natural disasters.

McCain and Obama both say the country must respond with a system to limit pollution from heat-trapping gases, a plan known as “cap and trade.”

But differences between the two candidates could produce very different outcomes. A plan to help stop global warming will require developing different sources of energy and a new system to use and pay for them. It also will reshape the nation's economy and security.

A cap-and-trade plan would force companies to buy permits for greenhouse gases. Those that find ways to cut emissions would need fewer permits and could sell unused permits to less efficient companies. The cap on total emissions would decline yearly. The next president and Congress are expected to work out the details.

Both candidates support mandatory emissions reductions through cap and trade. McCain's plan calls for a reduction to 1990 levels by 2020 and a 60 percent reduction from 1990 levels by 2050. Obama's plan has the same 2020 goal with an 80 percent reduction from 1990 levels by 2050.

NASA climate scientist James Hansen has said the next president and Congress “must define a course next year in which the United States exerts leadership commensurate with our responsibility for the present dangerous situation.”

Otherwise, he said, it will be impossible to cut the level of gases enough to prevent what Hansen called “disastrous climate changes that spiral dynamically out of humanity's control.”

McCain broke from the Bush administration's opposition to mandatory controls on emissions in 2003 and was among the first senators to push for a cap-and-trade plan. He chaired the first hearings that brought leading climate scientists to testify on Capitol Hill, and he led trips to remote parts of the globe to bring Senate colleagues to where scientists studied polar ice, oceans and the atmosphere.

Both candidates told that they accept the scientific agreement that greenhouse gases from burning fossil fuels are changing Earth's climate.

Obama: “There can no longer be any doubt that human activities are influencing the global climate and we must react quickly and effectively.”

McCain: “We know that greenhouse gas emissions, by retaining heat within the atmosphere, threaten disastrous changes in the climate.”

What they say they'd do

On coal: Coal produces half of America's electricity. McCain and Obama say the U.S. should invest in technology to capture carbon-dioxide emissions from coal-burning power plants. It's the only way to keep CO2 from coal out of the atmosphere, but it isn't close to commercial viability.

Obama would spend $150billion on clean energy over 10 years. He also would create a program to transfer clean technologies to developing countries.

Cambridge Energy Research Associates, which advises governments and energy companies, has estimated it will be at least two decades before technology to capture and store carbon dioxide from coal combustion is widely used.

Phasing out coal, except where carbon can be captured and stored underground, “is the primary requirement for solving global warming,” Hansen told a congressional panel in June.

McCain's Web site says “we cannot stop our use of coal” before carbon capture and storage is widely available. His campaign launched a Coalition to Protect Coal Jobs to discuss the “advantages of tapping the country's vast coal reserves.”

McCain would invest $2 billion per year for 15 years to find ways to permanently store greenhouse gas emissions from coal.

Obama's plan says the U.S. should “prevent a new wave of traditional coal facilities.”

On federal investment in clean energy: Obama's $150 billion over 10 years would also cover such things as cleaner cars and more efficient buildings. McCain has called for a $5,000 tax credit to people who buy zero-emission cars and a $300million prize for better batteries for plug-in hybrids and all-electric cars.

On renewable energy: Both candidates say they support tax benefits for wind and solar. McCain voted against them in the past, or didn't vote. In December 2007, the Senate failed by one vote to move ahead with a measure to extend tax credits to wind and solar energy and cut tax advantages for the oil industry. McCain was the only senator who didn't vote. Obama and his running mate, Joe Biden, voted for it.

On nuclear power: It's a primary element of McCain's emissions-reduction plan. He wants 45 new reactors built by 2030. Obama has said more nuclear energy likely will be needed, but issues with nuclear-waste disposal must be resolved first.