Todd Stern, the special envoy for climate change at the State Dept., faced tough questions from members of a House subcommittee over the size of U.S. contributions to an international effort to help developing countries adjust to global warming.

Rep. Rohrabacher, R-Calif., chairman of the House Foreign Affairs Oversight and Investigations Subcommittee, offered a blunt assessment of the odds that the United States will be paying a large share of the $100 billion annual fund agreed to during international climate talks last year in Cancún, Mexico.

“With a federal budget in massive deficit and an economy that is still trying to pull itself out of a deep recession, the expectation that the U.S. will be footing a major share of the bill for such a fund is pure fantasy,” Rep. Rohrabacher said.

The United Nations fund — which was one of the few tangible results of the global climate talks in December ‘09 — is aiming for $100 billion in contributions by 2020.

Stern declined to provide estimates of how much the United States would contribute, but downplayed the notion that it would come from the federal government.

“A great majority of it will come from the private sector,” he said. However, the policies he suggested for encouraging such investment - including a cap-and-trade scheme, clean energy standard, or tax incentives - all face uphill fights in the current political environment. Stern called it “vital to U.S. diplomatic leverage generally and to long-term U.S. interests in the world” to be engaged in climate talks, regardless of belief in the phenomenon or the science. “It would hurt us diplomatically,” he said.

The United States currently is preparing for follow-up talks planned for later this year in South Africa, where the funding for developing nations is again expected to be a dominant issue.