A key House Energy and Commerce subcommittee today heard from a diverse panel of witnesses who disagreed over the need for U.S. EPA to regulate greenhouse gas emissions and the likely economic effects of such rules.

The hearing comes after EPA proposed its first new source performance standards for new power plants in March and as a federal appeals court continues to weigh industry legal challenges to EPA's carbon dioxide program.

In their opening remarks, Energy and Power Subcommittee Republicans attacked EPA's plans as an unnecessary drag on economic recovery and as a regulatory overreach.

"At a time of chronically high unemployment, the last thing job-creating industries need is more red tape," said subcommittee Chairman Ed Whitfield (R-Ky.). "But that is precisely what EPA is imposing on the economy with its greenhouse gas regulations."

"We are already seeing the agency's greenhouse gas permitting requirements acting as one more roadblock to the economic recovery and to job growth," said Rep. Fred Upton (R-Mich.), chairman of the full committee.

Upton said he was "proud" to have sponsored a bill last year that would have stripped EPA of its authority to regulate heat-trapping emissions linked to climate change. The bill cleared the House but has stalled in the Senate.

Only Rep. Joe Barton (R-Texas), the former chairman of the panel, waded into the question of climate science by saying that U.S. curbs on industrial emissions would have a minuscule effect on global temperatures but a staggering cost.

Barton said that when the Clean Air Act and its amendments were being debated, climate change did not figure in those discussions.

Carbon regulation under the statute is the result of a 2007 Supreme Court case ruling, but Barton said Congress should fix that.

"I would prefer that we would simply exempt in statute, that would be my solution," he said.

But committee ranking member Henry Waxman (D-Calif.) said bills like Upton's were an attempt to legislate away scientific fact. "Instead of examining the science, House Republicans have voted that climate change does not exist," said Waxman, who sponsored a bill in the previous Congress that would have set up a cap-and-trade program to curb emissions.

Republican efforts to "deny the laws of nature" would not protect the U.S. economy, he said.

"The price of this denial will be paid by the American entrepreneurs, workers and communities that want to participate in the clean energy economy in the future," he said.

The subcommittee heard from representatives of the baking, electricity generation and petroleum industries, and from environmentalists and one scientist --- a possible concession to repeated requests from Waxman and subcommittee ranking member Bobby Rush (D-Ill.) to hold another hearing on climate science.

Robb MacKie, president and CEO of the American Bakers Association, focused his remarks on what would happen if EPA's tailoring rule were overturned in court and small emitters releasing as little as 250 tons of carbon dioxide a year were suddenly subject to regulation. The cost of the hypothetical regulation would be crippling to bakeries, he said.

Carl Shaffer, president of the Pennsylvania Farm Bureau, took a similar tack in his remarks. EPA Administrator Lisa Jackson has stated that her agency does not intend to regulate greenhouse gases from agriculture, he acknowledged, but the Clean Air Act gives EPA no authority to exempt the sector. Congress must act to ensure that farmers and ranchers do not have to apply for costly permits to operate, he said.

"The sad part of it is there is no environmental benefit to attaining the permit, that's the sad part," he added.

Daniel Weiss, senior fellow and director of climate strategy for the Center for American Progress, said that industry groups including the American Petroleum Institute are behind legal attempts to overturn the EPA tailoring rule, which would bring about the effects MacKie and Shaffer say they fear.

William Chameides, dean of the Nicholas School of the Environment at Duke University, sought to head off GOP arguments that the federal government should wait until climate science is more settled than it is today to act to reduce emissions.

Chameides said that scientists know that climate change is occurring and is very likely to be driven by human emissions.

"We can expect always to face some uncertainties about future climate risks," he said. "But the uncertainty is not a reason for inaction. Indeed, uncertainty cuts both ways."

Projections are as likely to underestimate the damage climate change could do to public health and the economy as to overestimate it, he said.

Chameides also fielded questions about whether carbon dioxide presents a genuine threat to public health. He said that while inhaling high-CO2 air does not cause damage, the climate effects of greenhouse gases would.

"I think we can all agree that heat waves kill," he said. "That's the kind of risks that we face with global warming, and I would say it's a pretty substantial public health risk."

But Barton countered that if direct exposure to CO2 does not cause illness and death, it should be exempted through regulation from regulation under the Clean Air Act. He proposed arming vulnerable populations with heating and cooling systems to protect them from the health effects of climate, a solution he said would be less costly than mitigation.