John McCainJohn Sidney McCainGOP rushes to cut ties to Moore GOP strategist: 'There needs to be a repudiation' of Roy Moore by Republicans World leaders reach agreement on trade deal without United States: report MORE proposed Monday binding limits on emissions to try to stem global warming, breaking from policies supported by President Bush and most Republicans.

McCain called for a cap-and-trade system allowing companies to purchase the rights to produce emissions, blamed for rising temperatures around the world. Such a system would be in line with free-market principles, he said.

"Those who want clean coal technology, more wind and solar, nuclear power, biomass and bio-fuels will have their opportunity through a new market that rewards those and other innovations in clean energy," McCain said in a speech in Portland, Ore. "The market will evolve, too, by requiring sensible reductions in greenhouse gases, but also by allowing full flexibility in how industry meets that requirement."

By 2012, McCain seeks to reduce U.S. emissions to the level they were at in 2005. By 2020, he called for a reduction to 1990 levels, and, by 2050, to levels equivalent to 60 percent of 1990 levels.

Bush and other Republicans have opposed binding emissions caps. Though McCain didn't name the president's climate change policy Monday, he dismissed it as government inaction.

"I will not shirk the mantle of leadership that the United States bears," he said. "I will not permit eight long years to pass without serious action on serious challenges. I will not accept the same dead-end of failed diplomacy that claimed Kyoto. The United States will lead and will lead with a different approach -- an approach that speaks to the interests and obligations of every nation."

The Democratic National Committee sent out a memo ahead of McCain's Monday address questioning his commitment to addressing climate change. It noted that four of McCain's donors are CEOs of companies with records of polluting the environment or undermining protected areas.

"As is so often the case with John McCain, this is yet another example of his effort to have it both ways on an issue," the DNC's memo read. "But how can Americans trust him to be a good steward of the Earth when the people advancing his political career are on the wrong side of the issues?"