Former President Bill Clinton took aim today at lawmakers who are blocking legislation to reduce U.S. greenhouse gas emissions, saying that the scientific proof of their potential harm has only gotten stronger since Congress blocked Clinton's own administration from signing an international climate change treaty 15 years ago.

"We're the only major country in the world that has one political party where apparently it's ideologically imperative to deny the reality of climate change," Clinton said at an Energy Department conference this morning.

As first steps, he said, the United States needs to move swiftly on energy efficiency and take steps to clean up other climate-changing substances besides carbon dioxide.

Rather than allowing landfills to release methane, which is more than 20 times as potent as carbon dioxide, the country should take steps to recover the gas and use it for energy, Clinton said.

Under the leadership of his wife, Secretary of State Hillary Rodham Clinton, the Obama administration has backed an international program that aims to bring cleaner cooking stoves to the developing world. Scientists say soot from stoves burning coal and biomass kills tens of thousands of people per year, and it also has a potent effect on the climate because its dark color absorbs heat.

Beyond those moves, there are "wildly profitable ways" to reduce carbon emissions and expand the U.S. economy, Bill Clinton told the crowd at the Advanced Research Projects Agency-Energy conference outside Washington, D.C. He called for more funding for the agency, which is getting $275 million this fiscal year and would get $350 million under President Obama's proposal for next year.

"Our economic future is not threatened by what you're doing -- it depends on the success of what you're doing," Clinton told technology developers at the event.

Cautious support for fracking, Keystone XL

Despite his concerns about the use of fossil fuels, Clinton said he supports the renewed oil and gas development that has boosted the economy in many parts of the United States, even driving the unemployment rate in North Dakota down to the low single digits.

"I like this 'all of the above' strategy, as long as we are moving toward a substantial reduction in greenhouse gases, with [economic] growth," he said of fossil fuel development.

America needs to end its "ambivalence" about natural gas, and more specifically the hydraulic fracturing process used to crack underground rock formations and release the gas inside, he said.

"We're going to take that out of the ground. It's obviously happening," he said.

And Clinton blamed developer TransCanada Corp. for the delay of the Keystone XL pipeline, which Obama blocked after House Republicans forced the State Department to speed up its review, but he said the $7 billion project should still proceed.

The first route proposed by Transcanada for review by the State Department would pipe Canadian oil sands through the Ogallala Aquifer, which provides drinking water to much of the Midwest, as well as Nebraska's sensitive Sandhills region. Clinton said that makes no sense because the extra cost of routing the pipeline around the Sandhills would be "infinitesimal compared to the revenues" from running the pipeline.

TransCanada told the State Department on Monday that it will submit a new application to build a pipeline from the Canadian border, as well as begin construction immediately on the southernmost section of the pipeline, connecting the crude oil hub in Cushing, Okla., to refineries in Houston.

"I think we should embrace" the plan to reroute the pipeline around the Sandhills "and develop a stakeholder-driven system of high standards for doing the work," Clinton said.