IF YOU WANTED fireworks, you're going to have to wait for the Fourth of July.

The tone was low-key, but the policy contrasts were sharp as Gov. Corbett and his fall challenger, Tom Wolf, offered their visions for Pennsylvania's environment last night on a Philadelphia stage - their first joint appearance since Wolf won the Democratic nomination for governor last month.

Speaking back-to-back to the Pennsylvania Environmental Council in Center City, the dueling Toms barely acknowledged one another - although the balding Wolf did offer the contrast that the ivory-topped Corbett has "too much hair on top of his head." And both spoke in nearly identical terms of finding balance between creating jobs and preserving the environment.

But there were devilish differences in the details.

Corbett spoke nostalgically of how far Pennsylvania has come since his Boy Scout youth of paddling down polluted Pittsburgh rivers, and he hailed the current impact fee on gas drillers that he said has brought in $630 million in three years.

"Before I took office, most of the debate around Marcellus [shale gas] was about the ways we could turn it into revenue right away for government to spend," the Republican governor said. "Now everybody ought to pay their fair share . . . and they do."

Wolf, on the other hand, spoke of issues that Corbett never mentioned during his 21-minute address - including tackling climate change and greenhouse-gas emissions, and harnessing wind and solar power.

The York County businessman and former state revenue commissioner also said a severance tax on fracking wells - Wolf has said he favors a 5 percent levy - would "provide certainty" for industry as well as for a state struggling with budget woes. He said that a tax - which Corbett vehemently opposes - would "help Pennsylvania's schools and could go a long way to making sure that the industry has a strong workforce that is grown and educated right here in Pennsylvania."

Wolf also won a smattering of applause when he said he wants Pennsylvania to consider joining the Regional Greenhouse Gas Initiative, an effort among nine states to reduce the types of pollution linked to global warming.

The environment has loomed larger in 2014 than in past gubernatorial races. Wolf - who starts the general election with a sizable lead in the polls - is expected to be aided by millions of dollars from California billionaire Tom Steyer, a global-warming crusader, while Corbett is raising significant dollars from oil and gas executives.

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