UNITED NATIONS (AP) – In a major shift, the United States committed itself to reaching agreement on a new global climate treaty this year and told the U.N. it wants strong targets for cutting greenhouse gases as long as other heavily polluting nations do their part.

The document represents President Barack Obama’s first move in the complex negotiating process with virtually all the world’s nations leading up to final treaty talks in December in Copenhagen, Denmark.

But the formal notice to the U.N. that the United States, unlike during the Bush administration, now intends to join the climate treaty did not include any specifics for achieving what it called “a low-carbon strategy for long-term net emissions reductions by 2050.”

The new global warming treaty is being crafted to succeed the first phase of the 1997 Kyoto Protocol, which requires 37 industrialized nations to reduce greenhouse gas emissions an average of 5 percent below 1990 levels by 2012.

The United States is the only industrialized nation that did not ratify Kyoto, but it agreed with more than 180 other nations at a conference in Bali in December to negotiate a new agreement by the end of this year.

The Nobel Prize-winning U.N. network of climate experts and other scientists has repeatedly warned that rising seas, droughts, severe weather and other dire consequences will result without sharp cutbacks in emissions of the industrial, transportation and agricultural gases blamed for warming.

The U.S. “will be submitting additional proposals as the negotiations progress,” the administration told the U.N.

Obama campaigned on a pledge to reduce U.S. emissions to 1990 levels by 2020, a dramatic turnabout from former President George W. Bush’s stance that Kyoto would have caused too much harm to the U.S. economy and was unfair without requiring similar cutbacks by developing nations.

Ban Ki-moon, the U.N. secretary-general, said Tuesday he was satisfied with the U.S. submission, despite its lack of specific goals for cutting carbon dioxide and other climate-warming gases.

“I know that there is … some more to do by the United States government, but this is a good step and I would encourage further that the United States take more concrete, more bolder initiatives,” he said in answer to a reporter’s question.

A Copenhagen treaty could shape the course of climate change for decades to come, particularly if fast-developing nations such as China and India agree to limit their emissions as well.