Barack Obama

President Barack Obama will seek to galvanize international support in the fight against climate change on Tuesday when he addresses the United Nations, with time running out on his hopes of leaving a lasting environmental legacy.

Obama has warned that failure to act on climate change would be a “betrayal” of future generations, but faced with a Congress reluctant to even limit greenhouse gas emissions — let alone ratify an international agreement — his options appear limited.

Tuesday’s climate summit in New York kicks off a process that will culminate in Paris at the end of 2015, where the world’s powers will hope to seal a new global climate change pact.

“Internationally, this is the opportunity for the president to leave his mark on the issue,” said Alden Meyer, of the Union of Concerned Scientists, a Washington-based think-tank.

Obama’s last meeting with heads of state to try to strike a climate deal, in Copenhagen five years ago, ended in bitter disappointment.

“I think that people are justified in being disappointed about the outcome in Copenhagen,” Obama said at the time, lamenting the failure to agree a timetable to reduce emissions over the coming decades.

– Complicated landscape –

Five years after that setback, the landscape remains complicated.

“I think that there is some greater sense of perhaps realism as well as ambition among parties than perhaps there was in 2009,” said Todd Stern, the United States top climate negotiator.

“I think, at the same time, these negotiations are always difficult,” he said in a recent conference call.

In the short term, it remains highly unlikely that the 120 heads of state and government due to attend Tuesday’s one-day meeting in New York will meet the expectations of UN Secretary General Ban Ki-moon, who has called for “bold pledges” to be made.

The White House has said it will not announce its post-2020 goals in New York this week, but rather plans to roll an out ambitious target early next year according to John Podesta, Obama’s adviser on climate and energy.

“You can expect the US to make public by the first quarter of 2015 a strong national target for reducing greenhouse gas emissions in the post-2020 time frame,” Podesta said.

“The President will use his speech at the Climate Summit to call on other leaders to keep their ambition high and to work toward a strong global framework to cut emissions.”

For the time being, the Obama administration will highlight the measures it has taken in recent months to reduce the consumption of fossil fuels.

– Ambitious 2030 goal –

In June, Obama unveiled new standards aimed at achieving a drastic reduction in carbon emissions from all existing power plants — a 30 percent reduction of 2005 levels by 2030.

But the White House has delayed addressing the difficult debate surrounding the legal nature of the agreement that 195 nations in the UN Convention on Climate Change will hope to reach in Paris at the end of next year.