Newt Gingrich was always considerably more environmentally conscious than most of his conservative Republican colleagues in Congress.

In the early 1970s, before he entered politics, Gingrich taught a college course in environmental studies.

And he continues to espouse a conservative brand of conservation that he calls "mainstream environmentalism" in a new book called A Contract with the Earth, which he co-wrote with Terry Maple.

The former speaker of the House says he grew up a conservationist and that there was nothing inconsistent about been green and being Republican — until later.

Starting in the 1980s, Gingrich says that "the leading environmental groups on the left — particularly the Sierra Club and the League of Conservation Voters — began to equate the environment with litigation, regulation, taxation, bureaucracy."

"And you were either for their solution or you were against the environment," Gingrich tells Robert Siegel.

That turned off many Republicans.

Gingrich discusses how, in fact, the Republican Party has a history of conservationism — for example, Republican President Theodore Roosevelt is considered the father of modern federal conservation efforts and of the national forests.

Part of the motivation for writing Contract with the Earth, Gingrich says, was to explain that it's possible to have a science-and-technology-based, entrepreneurial, free-market approach that incentivizes the development of new systems and new technologies that can lead you to a better environment.

He says this approach is "faster" and has a "greater likelihood of achievement than you're going to get by focusing on regulation and litigation and bureaucracy and trial lawyers."

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