U.S. President Barack Obama will go to the global climate summit in Copenhagen next month, a White House official said Wednesday.

The United Nations welcomed the move, saying the presence of the U.S. leader would be crucial to advancing talks on global reductions to greenhouse-gas emissions.

"I think it's critical that President Obama attend the climate change summit in Copenhagen," Yvo de Boer, the UN's climate treaty chief, told reporters in Bonn, Germany, on Wednesday.

"The world is very much looking to the United States to come forward with an emission reduction target and contribute to financial support to help developing countries."

Obama will appear at the summit on Dec. 9 before heading to Oslo to accept his Nobel Peace Prize, according to a White House official.

Prime Minister Stephen Harper is not planning to attend, according to his office, as Canada considers the summit a ministerial event. His office said Harper would consider going if the summit turns into a full-fledged conference of world leaders.

At least 65 world leaders are expected to be there, but unlike Obama, most are expected to attend the final days of the conference, which runs from Dec. 7 to 18.

Summit unlikely to produce pact

The Copenhagen summit had long been anticipated as a potential forum for establishing a new global climate pact. But politicians around the world, including Canadian Environment Minister Jim Prentice, have signalled the meetings are unlikely to produce a replacement for the Kyoto Protocol.

The 1997 protocol only required 37 industrialized nations to cut emissions, and the lack of participation of the United States and China — the two largest emitters of greenhouse gases in the world — helped undermine its effectiveness.

The UN had hoped the U.S. under Obama would not only join a new agreement, but also help lead the way for others to participate. As a possible step in that direction, administration officials said earlier this week that the U.S. will present a target for reducing carbon dioxide emissions at the summit.

Emissions-reduction targets are already being dealt with by the U.S. Congress. A bill passed by the House of Representatives requires a reduction of carbon dioxide and other greenhouse gas emissions by 17 per cent from 2005 levels by 2020, while a bill before the Senate seeks a 20 per cent reduction over the same time period.

The European Union has urged other developed countries to match its more ambitious pledge to cut emissions by 20 per cent from 1990 levels by 2020, and has said it would cut up to 30 per cent if other developed countries follow suit.

The Conservative government in Canada has pledged to lower greenhouse gases 20 per cent from 2006 levels by 2020. That objective has drawn criticism from opposition leaders for being calculated not on fixed emissions, as the European targets are, but on an intensity basis, meaning emissions would be tallied relative to the economic output of various industries.

With files from The Associated Press