Sen. Mark Udall and Rep. Cory Gardner

NASA HQ PHOTO | House GOPSen. Mark Udall (D) is defending his seat against Rep. Cory Gardner (R).

The U.S. Senate race in Colorado — which is a dead heat in the latest polls — pits a climate hawk against a climate change denier. The outcome may hinge partly on environmental issues, and it may also determine control of the Senate.

Republicans need to pick up six seats to take the Senate. Luckily for the GOP, Democrats have to defend a number of seats in red and purple states, many with significant fossil fuel interests, including West Virginia, South Dakota, Montana, Arkansas, Louisiana, North Carolina, Alaska, Michigan, Iowa, and Colorado. Given that Democrats are vacating some of these seats — and are lucky ever to have won in some of the redder states — holding Colorado is essential to any map in which Democrats retain the majority.

In some of these races, like with Mary Landrieu in Louisiana, the Democratic incumbent has such an anti-environment record that greens are not motivated to help, even though the Republican would be worse.

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But Colorado is different. The fact that it is a swing state disguises that it is not so much moderate as idiosyncratic. It encompasses liberal, pro-environment bastions of crunchy culture like Boulder. But it also has oil, natural gas, coal, ranchers, and Evangelical Christian outposts like Colorado Springs. In the greater Denver area, the highly educated workforce leans left while the state’s vast rural expanses are staunchly conservative.

Democrats who win statewide office carefully balance these competing interests. Gov. John Hickenlooper (D), who is up for reelection this year, has struck finely calibrated positions on hot-button issues such as natural gas fracking and marijuana legalization. He supports hydraulic fracturing, and opposes efforts to regulate it at the local level, but he also produced the nation’s first state-level restrictions on methane leakage from fracking operations. Republicans, on the other hand, are much too irrational and self-righteous to mimic this strategy. In recent years, their preferred approach in Colorado has been to nominate unelectable extremists like Ken Buck and lose.

Both of these partisan traditions are on full display in this year’s Senate race. The Democratic incumbent, Mark Udall, has a strong environmental record. His lifetime voting score from the League of Conservation Voters is 97 percent. He unequivocally supports efforts to address climate change, and he’s pushing to renew tax credits for wind energy. But he also backs his state’s fossil fuel industries, including the booming fracking sector. Both Udall and his likely Republican opponent, Rep. Cory Gardner, are sponsoring bills to speed up exports of liquefied natural gas, and both make the specious argument that doing so would deter Russian aggression in Ukraine.

Aside from their shared affection for natural gas, however, Gardner and Udall’s environmental records could not be more different. Gardner is intensely conservative across the board. His lifetime LCV score is 9 percent, thanks to votes against even modest measures like one that would have allowed the Nuclear Regulatory Commission to issue updated safety regulations after the Fukushima Daiichi disaster. Gardner admits that the climate is changing but not that humans are responsible; he majored in political science and went to law school, so he must know more than 97 percent of climate scientists.

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In a swing state such as Colorado, this kind of matchup would tend to bode well for the Democrats. But 2014 is an off-year election. The electorate that comes out in presidential years, and that has delivered Colorado twice for President Obama, is younger, more racially diverse, and more Democratic than the smaller off-year electorate. Republicans have an advantage among the older, white voters who show up for the midterms. This means Gardner very well could win. Statistician Nate Silver gives Udall a 60 percent chance of hanging onto his seat.

This makes environmentalists very nervous. Democrats losing the Senate would be bad for the environment, and it would be even worse if the losses came from pro-environment senators like Udall instead of fossil-fuel defenders like Landrieu or, say, Arkansas’ Mark Pryor. And so greens are getting actively involved in the campaign. In April, LCV added Gardner to its “Dirty Dozen” list of targeted anti-environment candidates, and initiated a $1 million television ad campaign highlighting his subservience to Big Oil. The first commercial pointed out that Gardner has taken more than $450,000 in campaign contributions from the oil and gas industry and rewarded it by voting to protect its special tax breaks. The second noted that the out-of-state, fossil-fuel baron Koch brothers are spending $1 million on Gardner’s behalf. The LCV Action Fund, which raises money for candidates, has already brought in more than $120,000 for Udall. (Billionaire climate campaigner Tom Steyer has not gotten involved in the race thus far, probably because Udall has not taken a stance on the Keystone XL pipeline.)

Environmentalists can, like any bunch of liberals, help Udall win by giving him money or by attacking Gardner. But it’s not clear how much environmental arguments themselves will resonate with a midterm electorate in Colorado. Udall’s campaign has thus far overwhelmingly emphasized Gardner’s extreme conservatism on more typical hot-button issues like abortion. That’s a proven move from the Democratic playbook in Colorado, where swing voters lean liberal on social issues.

A Quinnipiac poll conducted in mid-April found Coloradans evenly split between Udall and Gardner, 45-44. Another poll, released by LCV on Monday, put Udall up a couple more points, 47-43, and it found that the percentage of voters with a negative view of Gardner has spiked from 25 to 42 percent since mid-March.

The Quinnipiac poll also asked the state’s voters about their priorities, and found that 4 percent of them rate the environment as their top issue, which is unusually high. (In national polls, it’s usually around 1 percent.) But that lags behind the economy, which garners 10 percent. Jobs are the top issue for 5 percent, energy/gas/oil for 1 percent, and fracking for 1 percent.

Michael Stratton, a Democratic political consultant in Colorado, explains that the environment does matter more to Coloradans than to most American voters. “The most important issues to Coloradans, transcending elections and cycles, is quality of life,” he says. “The No. 1 thing people say in surveys over several elections is their top concern is quality of life. That includes the environment, but it is not specific to any one issue.” Colorado is a state where many people have moved relatively recently from other parts of the country for the high quality of life, including clean air and mountain views.

But, says Stratton, jobs and economic anxiety are the other main concern for Coloradans. A clean environment attracts some employers and is crucial for the state’s large tourism industry. And yet the oil and gas industry is a big source of jobs. That leads to the tension of Coloradans wanting both environmental protection and fossil fuel exploitation. Udall embodies this tension. In the words of Kim Stevens, campaign director for Environment Colorado, Udall is both “a huge champ on climate change” and, borrowing a phrase from Obama, “an ‘all-of-the-above’ energy guy.”

Though Udall has not made climate change much of an issue so far, his campaign decided to play it up on Monday, seizing on an opportunity to link Gardner to controversial comments by Sen. Marco Rubio (R-Fla.). Rubio, a presidential hopeful who recently endorsed Gardner, said in a TV interview on Sunday that he doesn’t think humans can have an impact on the climate. “Cory Gardner & Marco Rubio: Wrong on Climate Change,” the Udall campaign declared in a press release. “Droughts. Floods. Wildfires. Wild swings in snowpack. All are serious issues impacting Coloradans and our state’s economy. And all are significantly exacerbated by the effects of a rapidly changing climate. … Despite the very real impacts that climate change is already having in Colorado, Congressman Gardner and his Washington backers continue to deny the facts while refusing to take action to protect Colorado’s interests.”

If that charge seems to stick, Udall might hammer on the issue of climate change in more ads and in stump speeches. If not, he might keep emphasizing reproductive rights and efforts to raise the minimum wage. But whether or not he talks much about the environment, this race is a critical one for people who care about clean energy and climate change.