Obama will address delegates from 192 nations on 9 December before flying to Oslo to accept the Nobel Peace Prize. He is not expected to return for the final days of the summit when more than 70 world leaders are scheduled to attend.

Obama’s decision to attend the summit had been expected as he was under intense pressure to do so from European leaders, officials in developing nations and environmental groups.

In a statement, the White House says Obama is “prepared to put on the table a provisional US emissions reduction target in the range of 17% below 2005 levels in 2020.”

The “expected pathway” to achieve Obama’s goal to reduce emissions 83% by 2050 is to bring them down 30% by 2025 and 42% by 2030, the statement adds.

“This provisional target is in line with current legislation in both chambers of Congress and demonstrates a significant contribution to a problem that the US has neglected for too long,” it notes.

The US, the second largest global emitter of heat-trapping gases, has been unable to present firm medium- or long-term reduction targets because of gridlock over climate change legislation in the US Senate.

Several observers have questioned whether it makes sense to set a goal while running a risk that Congress will not embrace it.

“Obama makes a tremendous assumption with how Congress will act,” Manik Roy, vice president for federal government outreach at the Pew Center on Global Climate Change, tells Recharge.

Before making any firm pledges, he adds, “Obama would be well-advised to consult carefully with moderate senators from both parties.”

As an example of presidential overreach, he cites Bill Clinton, who commited the US to the Kyoto treaty only to have the Senate vote down ratification. His successor, George W. Bush, wanted nothing to do with it.

Delegates are not expected to reach a legally binding agreement in Copenhagen and instead, reach an outline for future action to slash greenhouse gas emissions.

Most American environmental groups believe it is important that Obama take part in the summit to reinforce the sea change in US policy on global warming since Bush left office.

The White House listed a host of policy decisions that Obama has taken to combat climate change, a move aimed at tempering criticism overseas over lack of firm US pledges to cut carbon pollution.

The White House also says that six senior US officials will also give keynote addresses at the summit. They are:

Lisa Jackson, Environmental Protection Agency administer, 9 December. She will speak on US efforts to reduce carbon pollution at home;

Ken Salazar, interior secretary, 10 December. His speech will focus on the role of public lands in clean energy production and carbon capture;

Gary Locke, commerce secretary, 11 December. He will speak on clean energy jobs in a global marketplace;

Steven Chu, energy secretary, 14 December. His talk will address US efforts to lead in energy efficiency and renewables;

Tom Vilsack, agriculture secretary, 15 December. His speech will focus on clean energy investments that create opportunities for rural economies.

Nancy Sutley, chair of the Council on Environmental Quality, 17 December. She will speak on translating international agreements into domestic action on environmental issues.