Virginia's gubernatorial race has become a test case in climate campaigning.

The two candidates, Republican state Attorney General Ken Cuccinelli and former Democratic National Committee chairman Terry McAuliffe, are prototypes: A Republican lobbing coal attacks and a Democrat alleging climate denialism in his opponent.

Fueling the dispute, the state chapter of the League of Conservation Voters has donated $900,000 directly to McAuliffe's campaign, the group and the campaign confirmed to ABC News, making it the largest donation to McAuliffe's campaign not to come from the Democratic Governors Association.

Cuccinelli and Republicans have been hammering McAuliffe for allegedly participating in a Democratic Party "war on coal," a leftover meme from the 2012 presidential campaign that has been given new life in Virginia with the Environmental Protection Agency pending release of new emissions caps for coal and gas power plants Thursday.

McAuliffe, 56, leads the race by 6 percentage points, according to the latest major poll released by Quinnipiac University in mid-August.

He has attacked Cuccinelli for his anti-climate-regulation stances. In Cuccinelli's recent book, "The Last Line of Defense: The New Fight for American Liberty," he expressed doubts about scientific consensus on climate change and its causes and questioned the designation of carbon dioxide as a pollutant.

Along with other state attorneys general, Cuccinelli also sued to try to prevent the EPA from regulating greenhouse gas emissions, a suit that ultimately failed in federal court.

McAuliffe's campaign has also accused Cuccinelli, 45, of a "witch hunt" in investigating University of Virginia climate scientist Michael Mann to see whether Mann had manipulated climate data while applying for state research grants. The probe was ultimately halted by the Virginia Supreme Court.

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As a state, Virginia has proven a unique battleground for coal and climate campaigning.

In the coal-producing region, Southwest Virginia was the target of coal-focused TV ads in last year's presidential race, and coal politics are heating up at the federal level, an issue that will soon force a response from McAuliffe.

Under a memorandum issued by President Obama in June, the EPA will issue new emissions caps for coal and natural-gas-fired power plants, and energy producers are already crying foul: Industry representatives warned Bloomberg News that the new rules would effectively ban construction of new coal power plants. For coal voters, the concern is that EPA regulations will cost jobs.

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But Virginia is also a coastal state, vulnerable to rising sea levels and more powerful storms, two effects associated with climate change. A July study by Benjamin Strauss of the global-warming-research and advocacy group Climate Central, Virginia Beach, Va., is among the three largest cities threatened by sea-level rise.

The Hampton Roads region, meanwhile, would face difficulties in evacuating under a major storm, and local transportation officials have raised concerns that evacuation routes aren't sufficient. The National Oceanic and Atmospheric Administration has said it is premature to conclude human activity has led to more powerful hurricanes, but it predicts that by the end of the 21st century, warming that results from human activity will have made hurricanes more intense on average.

Befitting this harshly negative race for governor, the candidates' differing views on energy have played out in a vicious TV ad war, plus other assorted shenanigans.

McAuliffe, who grew up in Syracuse, N.Y., is running a TV ad dubbed "witch hunt," hitting Cuccinelli for investigating Mann, the UVA climate scientist:

In a parallel campaign issue, Democrats have accused Cuccinelli's office of aiding energy companies at the expense of Southwest Virginia residents, the coal-country voters who typically vote Republican, and who should be a reliable voting base for Cuccinelli as he campaigns on coal.

Cuccinelli's office weighed in on a dispute about royalty payments to landowners. One of the companies, Consol Energy, has donated at least $86,000 to Cuccinelli's campaign, according to Virginia campaign-finance records. Cuccinelli's office has maintained its involvement in the case was limited and only served to uphold Virginia's Natural Gas Act.

A group called NextGen Climate Action Committee is airing two ads attacking Cuccinelli over the case:

Cuccinelli, meanwhile, is airing this ad that ties McAuliffe to Obama's "war on coal" and replays McAuliffe commenting, at a Democratic primary debate during his 2009 gubernatorial run, that "I never want another coal plant built":

With the new EPA regulations due to be released by the end of the week, McAuliffe has not yet taken a stance on them. But as National Journal's Coral Davenport has pointed out, for environmental groups, supporting McAuliffe isn't about backing a climate champion.

It's about staving off Cuccinelli, who opposes the notion that climate science is settled as stringently as anyone, and who points to the now-infamous East Anglia scandal as evidence that the numbers might all be cooked.

For the League of Conservation Voters, it might not matter what he says about those carbon caps, when they come out Friday. A spokesman for the group told ABC News that, whether McAuliffe supports or opposes them, it's "much better" to have him in office than his Republican opponent.