Can UN climate summit make real impact on rising temperatures?

New York City will be full of planet-saving pomp this coming week, but short on action to rescue the world.

More than 120 world leaders convene Tuesday for a U.N. summit aimed at galvanizing political will for a new global climate treaty by the end of 2015.

Environmentalists will take to the streets Sunday in what is being billed as the largest march ever on global warming. Celebrities, CEOs and climatologists will appear at a string of events as part of New York's annual climate week. "Titanic" star Leonardo DiCaprio will talk about what causes rising seas.

The hope is to recapture the momentum lost after the disappointing 2009 climate summit in Copenhagen, when world leaders left without a binding treaty.

The one-day U.N. summit, while not part of the formal negotiation process, is the pinnacle of the 7-year-old tenure of Secretary-General Ban Ki-moon, who has made fighting climate change his rallying cry and traveled the globe to personally invite world leaders to the gathering. Saying he was "humbled by the overwhelming response," Ban urged leaders to come with bold ideas.

Yet whatever happens at the U.N. summit is unlikely to bring the Earth closer to a goal set in Copenhagen: Preventing Earth's temperature from rising more than 2 degrees Fahrenheit from where it is now.

"Our expectation is this is a political event," said Zou Ji, deputy director of China's National Center for Climate Change Strategy.

Rather than firm commitments from closed-door negotiations, the summit is expected to jumpstart a series of much publicized initiatives and partnerships. Six oil companies will join with governments and environmental advocacy groups to slash methane leaks from the production of natural gas. There will be a massive commitment to combat deforestation. There will be initiatives announced to clean up agriculture and make freight shipments greener.

"Ultimately, we are going to need much more ambitious, concerted government action and government policies," said Nat Keohane, who worked as a special assistant to President Barack Obama on energy and climate issues before rejoining the Environmental Defense Fund in 2012. "This summit is not going to be one fell swoop where we are going to announce all those policies."

The U.S. heads into the summit in the strongest position it has been in years. It has cut emissions by 10 percent from 2005 to 2012, more than any other country. Officials say about half of that reduction is due to the economic recession, but it puts the U.S. well on its way toward meeting its goal to cut emissions by 17 percent by 2020 from 2005 levels.

White House officials said Obama will not be announcing any new targets at the summit but will leverage the progress the U.S. has made to pressure other major polluters like India and China to take more aggressive action.

"We are taking this summit seriously, both to show the world that the United States is committed to leading the fight about climate change and to call on the other leaders to step up to the plate and to raise their level of ambition to take on climate change," John Podesta, the White House's climate adviser, said in a conference call with reporters.

In Copenhagen, developing countries including China and India were exempt from setting greenhouse gas reduction goals. That is expected to change at the next climate change summit in Paris in late 2015, when all countries will be required to submit reduction targets for beyond 2020. Ji said China is already working on its targets and expects to unveil them in early 2015.

Already, evidence suggests that the 2009 temperature limit is an ever-more distant goal. Many experts believe it is nearly out of reach.

"We're nowhere close," U.N. Assistant Secretary-General Robert Orr said in a call with reporters. "It's really only the most aggressive of these scenarios that get us under 2 degrees."

Limiting warming to that level would require deep reductions in carbon dioxide pollution in the near term, but there is fear that countries will not offer nearly enough reductions next year to prevent temperatures from reaching the point where the changes brought about by climate change would be catastrophic.

"We are behind schedule, but we still do have time — just," former Vice President Al Gore said in an interview with The Associated Press.

In the weeks leading up to the summit, the World Meteorological Organization said that concentrations of carbon dioxide, the chief greenhouse gas, increased more in 2012 and 2013 than in any year since 1984. The months of May, June and August were the warmest of any on record in the United States. A study issued earlier this year said the West Antarctic ice sheet was starting to collapse and it was unstoppable.

"We're in a car heading toward a cliff, and while we're talking about how important it is that we put on the brakes, the car is meanwhile accelerating," said University of California Irvine scientist Steve Davis.

Connie Hedegaard, the top climate official for the European Union, told the AP that the best thing that could come out of New York is that governments at the highest levels will be forced to consider ambitious commitments well before a new deal must be reached at the end of 2015.

Associated Press Science Writer Seth Borenstein contributed to this report.