With the US presidential primaries now in full swing, climate change has emerged as one of the more divisive issues in an already combative race for the White House. The Democrat candidates are all openly addressing the issue, whereas the only clearly committed Republican is John McCain.

The League of Conservation Voters (LCV), a pressure group formed by a variety of conservation and strategy groups, has produced a guide for voters who are interested in where candidates stand on climate change. The guide reveals lukewarm attitudes by the Republican candidates on underlying issues such as cap-and-trade schemes, vehicle fuel efficiency and coal power.

The Democrats, meanwhile, are generally bullish on climate change measures. They all support two of the major issues underpinning climate change as outlined by the LCV: mandatory caps on carbon emissions, and emission reductions of at least 80 per cent by 2050.

The only Republican calling for emissions reductions by a certain date is the party's front runner John McCain, who along with Democratic candidates Hillary Clinton and Barack Obama, co-sponsored the Climate Stewardship and Innovation Act of 2007, which proposed cuts in US carbon emissions of 65 per cent by 2050.

Only three Republicans support a mandatory emissions cap. Mike Huckabee mirrors McCain's support for a cap, while Mitt Romney has said he will only support such a move it if it is enacted globally.

McCain's approach to mandating renewable energy, while not clearly articulated during this election campaign, was historically adversarial. The LCV - which wants 20 per cent of energy to come from renewable sources by 2020 - says that he opposed votes on mandating renewable energy levels in the past. Conversely, Democrat front-runners Clinton and Obama both want 25 per cent of US energy to come from renewables by 2025.

To varying degrees, all of the Democrat candidates support the LCV's view on the use of coal, which is a major source of carbon emissions. The organisation recommends a moratorium on any new plants unless they capture and store carbon emissions. Clinton supports a phased in approach, while Obama would consider a moratorium on new coal plants if a mandatory carbon emission cap did not slow their production. McCain, like every Republican candidate, supports the unrestricted use of conventional coal.

"What's scaring the American people is inaction on these issues. It's not just Democrats. It's independents in particular - those people in the middle, who will decide the election, and who have signalled over and over their willingness to take action on this", said LCV communications director David Sandretti, arguing that climate change is already a key issue for the US public. "We're looking at $100 per barrel oil, $3 per gallon gas, and home heating costs going through the roof."

However, despite many of the candidates support for carbon cutting measures the LCV warns voters to remain wary, citing broken promises in the past. President Bush promised to curb carbon emissions in his 2000 election campaign, it said, "then spent his entire term in office trying to stop and subvert efforts to do just that".