When news broke of Jon Huntsman’s serious consideration of a run for president last month, several conservative pundits, including the Washington Post’s Jennifer Rubin, dismissed the former Utah governor’s chances by pointing to his moderate record on global warming, which they predicted would play poorly among the GOP’s conservative base.

Indeed, Huntsman was a vocal booster of the Western Climate Initiative, which promoted the possibility of a carbon cap-and-trade program. “Until we put a value on carbon, we are never going to be able to get serious about dealing with Climate Change long term,” Huntsman said back in 2008. “Now putting a value on carbon either suggests you get a carbon tax or you get a cap-and-trade system underway.” This is obviously a long way from the current GOP orthodoxy on climate change, which holds that any attempt to regulate carbon is, as House Speaker John Boehner puts it, “a job-killing national energy tax on struggling families and small business.”

But Huntsman is far from the only 2012 GOP contender who will have to explain past support for confronting climate change on the campaign trail. In point of fact, carbon regulation was not so verboten in the GOP just a few years ago. Mitt Romney, Tim Pawlenty and Newt Gingrich all have supported efforts to combat climate change. “I also support cap and trade of carbon emissions,” Mike Huckabee declared in 2007, while campaigning in New Hampshire. In the same year, then-Alaska Gov. Sarah Palin set up a “Climate Change Sub-Cabinet” to deal with the problem in her state. Of the major candidates now inching towards a run, only Haley Barbour can boast of a clean record of opposing carbon regulation, dating from Barbour’s work as a lobbyist for heavily polluting energy companies.

So as a service to GOP voters preparing their early 2012 crib sheets, here is a quick-and-dirty look–in six parts, with video and links–of how this year’s potential candidates have approached the carbon issue:

1. Tim Pawlenty

The current Tim Pawlenty line on carbon is that “cap and trade would be a disaster.” He says he wants to reduce pollution, but not in a way that would burden the economy. Here he is on Meet The Press last year.

[youtube http://www.youtube.com/watch?v=ZJ6s2CTA8kg&fs=1&hl=en_US&rel=0%5D

Twas not always thus. As FactCheck.org points out, Pawlenty signed the Next Generation Energy Act of 2007 in Minnesota, which called for a plan to “recommend how the state could adopt a regulatory system that imposes a cap on the aggregate air pollutant emissions of a group of sources.” The plan would also allow “for a market-based trading of these allowances.”

In early 2008, Pawlenty cut a radio ad with then-Arizona Janet Napolitano–“against the background of inspirational, New Age-style music”–that urged Congress to pass national curbs on greenhouse gases. A Star-Tribune article from the time noted put it this way:

Alex Carey, spokesman for Pawlenty, said the governor is convinced of the need for action. Pawlenty plans another clean energy package in the coming legislative session and has adopted renewable energy as his signature issue during his tenure leading the National Governors Association.

The ad campaign was funded by the green group Environmental Defense.

2. Mitt Romney

On the pre-campaign stump, Mitt Romney regularly attacks Barack Obama for pushing a cap and trade system through Congress. In late 2009, he sent out a fund-raising appeal warning that the Obama cap-and-trade plan would have “a devastating impact on hard-working families.” But the Romney view on climate change has more often been one of nuance rather than sharp contrast. Here he is in Iowa in 2007, voicing concern about man-made global warming while supporting more government subsidies for new energy sources, new efficiency standards, and a new global carbon treaty.

[youtube http://www.youtube.com/watch?v=vnryDuV9_SI&fs=1&hl=en_US&rel=0%5D

In his latest book, No Apology: The Case for American Greatness, Mitt Romney pulls back a little. He is highly critical of cap and trade, a carbon tax and a new range of subsidies and standards to deal with global warming. He calls cap and trade “an energy tax that would have little or no effect on global warming.” He says the best option is probably a tax swap, which would increase taxes on carbon while off-setting the costs elsewhere, but he adds “a great deal of work remains to be done if it is to become a viable option.”

Romney also tries to deal in the book with his 2005 support, as Governor of Massachusetts, for a Northeastern regional cap-and-trade system. Romney writes that he was initially misinformed about the costs of the program he supported, which he says he thought would only raise energy bills by 3% to 5%. “When I met with the state’s major manufacturers, they produced estimates of 30 percent increases in rates,” Romney writes. “I didn’t sign on.”

That said, he cannot erase his past quotes. In 2005, he described a regional cap on carbon in much the same way as Barack Obama does today. “We can effectively create incentives to help stimulate a sector of the economy and at the same time not kill jobs,” he said. “I’m convinced it is good business.”

3. Newt Gingrich

In recent years, Newt Gingrich has taken to calling a federal tax on carbon “utterly irrational,” and “a Chinese full-employment act,” citing the need for global consensus on carbon regulation.

[youtube http://www.youtube.com/watch?v=gqgHvdPHzVM&fs=1&hl=en_US&rel=0%5D

But he was once far more bullish on the U.S. leading in an effort to reduce carbon emissions. In a 2007 interview with Frontline on PBS, Gingrich said:

I think if you have mandatory carbon caps combined with a trading system, much like we did with sulfur, and if you have a tax-incentive program for investing in the solutions, that there’s a package there that’s very, very good. And frankly, it’s something I would strongly support.

He also appeared in 2008 spot with Democrat Nancy Pelosi to announce “We do agree. Our country must take action to address climate change.”

[youtube http://www.youtube.com/watch?v=qi6n_-wB154&fs=1&hl=en_US&rel=0%5D

Gingrich has since tried to back away from the ad, saying he was only trying to help conservatives get their ideas in the climate change debate.

4. Sarah Palin

As a Fox News pundit, Sarah Palin has been a constant, fierce critic of President Obama’s efforts to combat climate change, which she has called the “job-killing, burdensome, cap-and-trade–I call it cap-and-tax–initiative.”

But back in 2007, she was not so down on exploring a wide range of steps to combat climate change. On September 14, as governor of Alaska, she signed Administrative Order No. 238, which established an “Alaska Climate Change Sub-Cabinet” to advise her on a wide range of possible measures to combat climate change, including “the opportunities to reduce greenhouse gas emissions from Alaska sources” and the potential benefits of participating in “carbon trading markets” or “in regional, national, and international climate policy agreements and greenhouse gas registries.”

“Many scientists note that Alaska’s climate is changing,” Gov. Palin announced at the time. “We are already seeing the effects. Coastal erosion, thawing permafrost, retreating sea ice and record forest fires affect our communities and our infrastructure. Some scientists tell us to expect more changes in the future. We must begin to prepare for those changes now.” Just four months after Huntsman had joined the Western Climate Initiative in Utah, Palin added Alaska as an “observer” to the group. Palin’s decision to join came just weeks after the group had pledged to seek reducing greenhouse gas emissions by 15% from 2005 levels by 2020.

A little more than two years later, on December 9, 2009, Palin penned a scathing opinion piece in the Washington Post where she questioned the evidence of a man-made role in climate change, and declared, “any potential benefits of proposed emissions reduction policies are far outweighed by their economic costs.”

5. Mike Huckabee

The former Arkansas Governor Mike Huckabee has been a long-time supporter of an economy-wide cap and trade policy, calling it a “moral issue.” “We have a responsibility to reduce greenhouse-gas emissions, to conserve energy, to find alternative forms of energy that are renewable and sustainable and environmentally friendly,” he said on a visit to New Hampshire in 2007.

[youtube http://www.youtube.com/watch?v=9yt3Q_98hl4&fs=1&hl=en_US&rel=0%5D

He has since tried to distance himself from these comments, saying in a 2010 press release that it was “just not true” that he had ever supported cap and trade during the 2008 campaign, and that it would be a “serious job killer.”

6. Haley Barbour

Probably no one in the current Republican field has been more deeply involved, or influential, in the climate change debate than Mississippi Gov. Haley Barbour. But his influence came largely before he entered elected political office, when he was a lobbyist working for energy companies fighting carbon regulation.

On March 1, 2001, Barbour wrote a letter to Vice President Dick Cheney, calling on George W. Bush to reverse a campaign pledge and put off regulation of carbon. “A moment of truth is arriving,” Mr. Barbour wrote. ”The question is whether environmental policy still prevails over energy policy with Bush-Cheney, as it did with Clinton-Gore.” Among Barbour’s clients at the time was the Electric Reliability Coordinating Council, a coalition of some of the nation’s largest coal-burning electric utilities, which were also major donors to the Republican Party.

“[W]e must ask, do environmental initiatives, which would greatly exacerbate the energy problems, trump good energy policy, which the country has lacked for eight years?” Barbour wrote. Two weeks after receiving the letter, President Bush announced a reversal of policy, though he denied that he had been influenced by industry lobbying.

Since then, Barbour has maintained his opposition to carbon regulation, often leading the charge. In April of 2009, he issued a call to fellow conservatives in an opinion piece in the Washington Times. “America needs more American energy, but the Obama policy is for less American energy and more expensive energy, he wrote. “Conservatives must wage and win the argument to show voters that President Obama’s energy policies mean higher utility bills and gasoline prices.”

His message on the presidential pre-campaign trail in 2011 has been much the same.