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Washington • Rep. Chris Stewart led his first hearing on climate change Thursday, where witnesses urged the government to greatly increase its investments in green-energy technologies but had differing opinions about taking sudden steps to cut carbon emissions.

Stewart, R-Utah, is the new chairman of the House environment subcommittee, and since taking office in January he has repeatedly expressed his skepticism that man-made climate change is as serious a threat as most of the scientific community and President Barack Obama have stated.

He points to scientific models that have overestimated rising temperatures, arguing that the modeling is not "infallible."

"We encounter those who claim to know precisely what our future climate will look like and then attack any who may disagree with them. When that happens, we have stepped out of the arena of science and into the arena of politics and ideology," Stewart said.

William Chameides, dean of the Nicholas School of the Environment at Duke University, acknowledged that modeling has overestimated climate change in some years but said "eventually the atmosphere catches up."

"My main message today is the risks posed by human-caused climate change are significant and warrant timely action to minimize these risks," he said. "Yes, there are uncertainties, but these uncertainties do not justify inaction."

Instead, Chameides argued for a flexible government response, but one that seeks to cut emissions as soon as possible to at least some degree. He said emissions from the first automobile remain in the atmospheres today, and those released now will be around for decades to come.

"We don't necessarily need to make major cuts now, we need to get started," he said.

Bjorn Lomborg, president of the Copenhagen Consensus Center, argued that the most effective way to combat climate change is to make green energy so cheap there is an economic imperative to stop using fossil fuels, but he said that day is far away and the only way to obtain it is to vastly increase the amount of funding going into research.

The political scientist called global warming "mostly man-made," and he said international attempts at tackling the problem in the last two decades "have done mostly nothing" — rather, richer countries have exported services that produce more pollution to developing nations like China.

"We are not polluting the atmosphere with CO2 simply to annoy the environmentalists, we are doing it simply because it's what powers everything we like," Lomborg said. "So unless we find technologies that allow us to continue economic growth without the CO2 emissions, I think we are going to find it very hard to get most nations on board."

Obama has promised to fight climate change in his second term, and with little traction for major congressional action, he has promised to seek executive actions to curb pollution. One possibility is to reduce carbon dioxide emissions from existing power plants.

Stewart said the president's comments cause him "great concern," largely for economic reasons.

"I am also concerned that his proposals will reduce our economic activity at a time when we can least afford to do that, while sending jobs overseas to countries such as China and India," he said.

Twitter: @mattcanham