The Republican Party still isn't sure global warming is man-made, one of the top Republican lawmakers on the House Select Committee on Energy Independence and Global Warming said this Earth Day.

"I don't know that there is a party position on this issue," Rep. John Shadegg (R-Ariz.) said Wednesday during an appearance on the Fox Business Network. "I think that there is some debate on whether global warming is in fact being caused by man-made greenhouse gases."

Shadegg is the second-ranking Republican lawmaker on the special House committee, which was established to help curb carbon emissions and global warming.

"Most Republicans would probably acknowledge that global warming is occurring; they're not certain the science yet is there on the issue of whether it's man-made," Shadegg said.

The Arizona lawmaker's comments come after House Minority Leader John Boehner (R-Ohio) said this past Sunday that the idea that carbon dioxide is affecting the global climate is "comical."

The comments also fall on today's "Earth Day" holiday, which is meant to highlight environmental stewardship.

For his part, Shadegg argued that the government should pursue green energy in addition to increased oil and gas exploration.

"If you start with those things that would give you a dual benefit," Shadegg explained, "that way if it later turns out it's not man-made greenhouse gases that are causing global warming -- if it's sun spots or something else -- we've still gained a benefit by reducing our reliance on all energy, and foreign energy in particular."

Shadegg said he preferred a straightforward carbon tax to the cap-and-trade system favored by the Obama administration, and accused congressional Democrats of arranging political favors to win the necessary votes on the cap-and-trade legislation.