Republican presidential nominee-in-waiting Senator John McCain of Arizona has offered his plan to combat global warming.

Speaking at the Vestas wind turbine factory in Portland, McCain said what America needs is market-based cap and trade system to curb greenhouse gas emissions, mobilize innovative technologies, and strengthen the economy.

McCain envisions a cap and trade system that would encompass electric power, transportation fuels, commercial business, and industrial business - sectors responsible for just below 90 percent of all emissions. Small businesses would be exempt.

By 2012, McCain says his plan would return greenhouse gas emissions to 2005 levels, which were 18 percent above 1990 levels.

By contrast, the Kyoto Protocol requires that by 2012 industrialized nations cut greenhouse gas emissions an average fo five percent below 1990 levels.

By 2020, McCain says his plan would return emissions to 1990 levels, and by 2030, McCain says his plan would cut emissions 22 percent below 1990 levels.

By 2050, McCain aims to achieve at least a reduction of 60 percent below 1990 levels.

By contrast, on April 16, President George W. Bush announced a new national goal to stop the growth in U.S. greenhouse gas emissions by 2025.

Democratic presidential hopeful Hillary Clinton said McCain's proposal does not go far enough. 'Real leadership means taking this problem head on with a comprehensive, science-based plan instead of halfway measures,' she said. 'While Senator McCain's proposals may be improvement on President Bush's, that's not saying much.'

Democratic presidential hopeful Barack Obama supports a market-based cap and trade system to reduce carbon emissions 80 percent below 1990 levels by 2050. Obama says this is the target scientists say is necessary to achieve.

Under McCain's plan, participants at first would be allowed to either make their own greenhouse gas reductions or purchase offsets, financial instruments representing a reduction, avoidance, or sequestration of greenhouse gas emissions to cover 100 percent of their required reductions. Offsets would only be available through a program dedicated to ensure that all offset emission reductions are real, measured and verifiable.

The fraction of greenhouse gas emission reductions permitted through offsets would decline over time. Emissions permits would eventually be auctioned to support the development of advanced technologies.

A public-private agency McCain calls the Climate Change Credit Corporation would oversee the cap and trade program, provide credit to entities for reductions made before 2012, and ease transition for industry with competitiveness concerns and fewer efficiency technology options.

McCain made clear his support for nuclear power as an essential part of the power mix, saying it 'requires exactly zero emissions' but not addressing the unsolved problem of nuclear waste storage. 'If we want to arrest global warming, then nuclear energy is a powerful ally in that cause,' he said today.

'We have many advantages in the fight against global warming,' McCain said, 'but time is not one of them.' Describing the melting glaciers he had seen in Norway and Alaska, and sustained drought in his own southwestern state, McCain said he is convinced that climate change is a real threat that demands response.

'We stand warned by serious and credible scientists across the world that the time is short and the dangers are great,' he said. 'The most relevant question now is whether our own government is equal to the challenge.'

The Democratic National Committee Chairman Howard Dean accused McCain of trying to cover up a record of not supporting funding for renewable energy, pointing out that in 2006 and in several earlier years, McCain voted against an amendment to extend the renewable energy production tax credit and clean renewable energy bonds programs. McCain voted twice against establishing national renewable energy standards,

'Senator McCain is once again trying to re-cast himself as a friend of the environment for the general election,' said Dean, 'but his record clearly shows that the only friends he really stands up for are his donors and the lobbyists running his campaign.'

League of Conservation Voters President Gene Karpinski said, 'To his credit, Senator McCain wants to do something serious about global warming, but his proposal falls far short of what the science says we need to do today.'