By Laurie Goering

LONDON (AlertNet) - Without a specific U.S. commitment to cut greenhouse gas emissions, negotiators will agree only a "very weak" global deal to curb climate change in Copenhagen next month, the U.N.'s top climate scientist predicted on Monday.

The new climate pact is designed to build on the existing Kyoto Protocol, with rich nations taking on deeper emission cuts and helping fund efforts in poorer nations to cut emissions and adapt to the effects of climate change.

But a negotiating session in Barcelona last week, the last before the Copenhagen meeting opens on Dec. 7, ended with limited progress. Nations from Africa - the continent expected to be hardest hit by climate change - at one point walked out of the talks in protest at what they saw as inadequate promises by developed nations.

Efforts to craft the new treaty are also being hit by the United States' struggle to pass domestic climate legislation - something it says is key to making a realistic international commitment - and as many of the other 190 negotiating nations jockey for political advantage.

"The general impression is we'll get some kind of statement (at Copenhagen) and then all the action will take place later," said Rajendra Pachauri, chairman of the U.N. Intergovernmental Panel on Climate Change, in an interview.

But with U.S. mid-term elections due next year, getting climate legislation through the U.S. Congress will not become easier in the coming year, he warned.

Other countries will not be motivated to commit to making ambitious cuts while the United States, the world's largest per-capita carbon emitter, remains outside a deal, he added.

"Without the U.S., what you get is a very weak kind of deal," said Pachauri, whose panel of scientists shared the 2007 Nobel Peace Prize with climate campaigner and former U.S. President Al Gore.

Pachauri urged U.S. President Barack Obama to strongly back efforts to get U.S. domestic climate legislation passed before Copenhagen.

"The U.S. president certainly has enough power to swing five or six senators from one side to the other," he said. "There has to be a concerted effort to get something out of the Senate. That would send a very powerful signal across the world."

He said efforts to promote climate change legislation in the United States and elsewhere have been handicapped in part by the worldwide economic downturn.

"The fact is people are worried about jobs. It's a major distraction and that's totally understandable," he said.

But politicians also have failed to adequately explain the financial and security benefits of curbing climate change, from greater energy security to a reduced risk of large-scale climate-induced migration and conflict.

He praised Europe for sticking to its unilateral commitment to cut emissions by 20 percent by 2020, saying a core group of commitments to action could still provide a basis for a "meaningful" global effort against climate change.

But he warned that current levels of international commitment to cuts would not avoid most of the dangerous effects of climate change, including sea level hikes, more severe storms, and increasing droughts and floods.

The world also should not rely on climate geo-engineering - emerging efforts to suck carbon out of the atmosphere or otherwise reduce climate change after it has happened - to protect itself, he said, calling such technology "a pipe dream".

"There are some many questions around it that I don't see it as a real possibility for the foreseeable future," he said. "I think we have enough knowledge, know what we are required to do, and we should just go ahead and do it."

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