Most major greenhouse gas emitters submitted their emissions-reduction plans to the United Nations in a move that infused with life an accord reached at a climate conference in Copenhagen last year.

As of Tuesday, 55 countries had sent in their action plans, including the United States, Canada, the 27 members of the European Union, India and China. Nations detailed their pledges to reduce emissions by 2020, some by naming concrete reduction targets, others by promising to make economic growth more sustainable.

The countries are responsible for nearly 80 percent of global greenhouse gas emissions, the United Nations said.

Yvo de Boer, the top U.N. climate official, said the national commitments invigorate negotiations aimed at coming up with a successor treaty to the Kyoto Protocol, which runs out in 2012.

"The commitment to confront climate change at the highest level is beyond doubt," de Boer said in a statement. "Greater ambition is required to meet the scale of the challenge. But I see these pledges as clear signals of willingness to move negotiations towards a successful conclusion."

Experts have blasted the so-called Copenhagen Accord, a text patched together in the final hours of the Copenhagen climate conference. The non-binding text was merely noted but not adopted by the 192 conference parties.

It sets the limit of global warming to 3.6 F and provides short- and long-term finance to help poor nations cope with climate change; it also set 2015 as a review year to see if global action needs to be more urgent to meet the challenge. But it remains a voluntary text, and even if nations commit to it, they are not legally bound to honor their pledges.

De Boer last month vowed that the accord could be of help as it will be used as "a political tool that … we can very usefully deploy to resolve the remaining issues in the negotiating process."

To meet the United Nations' soft Jan. 31 deadline, nations simply reiterated their previous pledges.

India and China promised to reduce their carbon intensities -- the level of CO2 emitted per economic unit -- by up to 25 percent and 45 percent, respectively.

The EU pledged to reduce its emissions by 20 percent by 2020 compared with 1990 levels, or even by 30 percent if an ambitious global deal is reached.

Washington promised to cut emissions "in the range of" 17 percent by 2020 compared with 2005 levels if the Senate endorses a corresponding climate-change bill.

Leading energy experts urged U.S. lawmakers to get behind this crucial U.S. climate legislation.

"The pledges made by countries like Japan, China, Europe and India show a commitment to collective, transparent action on a scale never seen before," Jennifer Morgan, head of the World Resources Institute's climate and energy program, said in a statement. "The United States should have no doubt that these countries plan to build their economies with clean energy."

The Senate, she added, "should act now to enact comprehensive climate legislation."