WASHINGTON — On the big picture, Barack Obama and John McCain agree — with a shared sense of urgency — that 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.
Scientists say the next president must take action on climate change. McCain and Obama both say that the country will need to respond with a system to limit the pollution from heat-trapping gases, a plan known for short as "cap and trade."
While their approach sounds similar, the differences between the two candidates could produce very different outcomes because the task is so enormous. 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 require companies to buy permits for greenhouse gases. Those that find low-cost ways to reduce emissions would need fewer permits and could sell unused ones to less-efficient companies that need them. The limit, or cap, on total emissions would decline every year. The next president and Congress are expected to work out the details.
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Both candidates say they 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.
Many congressional Republicans oppose an economy-wide cap-and-trade plan, but there's support for such regulation even from some large companies, including Shell, Chrysler and General Electric. They seek long-term planning certainty and prefer regulation that works through market mechanisms.
Princeton geosciences and international affairs professor Michael Oppenheimer said a cap-and-trade system is needed soon to form the basic framework of regulation. "I'm a big supporter of market-based incentives," he said.
NASA climate scientist James Hansen recently said that 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 become impossible to reduce the level of gases enough to prevent changes such as rising oceans and dying plant and animal species — what Hansen called "disastrous climate changes that spiral dynamically out of humanity's control."
Both candidates told the Web site sciencedebate2008.com 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."
Here's what the candidates say they'd do:
ON MANDATORY EMISSIONS REDUCTIONS
Both want a mandatory cap-and-trade system.
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 also chaired the first hearings that brought leading climate scientists to the witness table 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.
Coal produces half of America's electricity. McCain and Obama say the U.S. should invest in technology that would 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 $150 billion on clean energy over 10 years. He also would create a program to transfer clean technologies, including capture and storage of emissions from coal plants, to developing countries.
Cambridge Energy Research Associates, which advises governments and energy companies, has estimated that it will be at least two decades before the technology to capture and store carbon dioxide from coal combustion is widely used.
Phasing out coal, except where the carbon can be captured and stored underground, "is the primary requirement for solving global warming," Hansen, the NASA scientist, told a congressional panel in June.
McCain's Web site says that "we cannot stop our use of coal" before carbon capture and storage becomes widely available.
His campaign launched a Coalition to Protect Coal Jobs to talk about the "advantages of tapping the country's vast coal reserves" and protecting coal jobs, according to his campaign Web site.
McCain has said he'd invest $2 billion per year for 15 years to find ways to permanently store the greenhouse gas emissions from coal.
Obama's energy 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 $300 million prize for better batteries for plug-in hybrids and all-electric cars.
ON RENEWABLE ENERGY
Both presidential candidates say that 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 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 that more nuclear energy likely will be needed, but problems with nuclear-waste disposal must be resolved first.
WHAT THEIR RUNNING MATES SAY
McCain's choice, Alaska Gov. Sarah Palin, questions whether fossil-fuel combustion causes global warming.
"I'm not an Al Gore, doom-and-gloom environmentalist blaming the changes in our climate on human activity," she said in December.
Or, as she put it in the vice-presidential debate: "I'm not one to attribute every ... activity of man to the changes in the climate. There is something to be said also for man's activities, but also for the cyclical temperature changes on our planet." She went on to say that it wasn't important to know the cause.
Obama's running mate, Sen. Joseph Biden, D-Del., said in the debate that recent climate changes are manmade. He also has said that the U.S. must decrease emissions and lead in international climate talks.
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