President Barack Obama will seek to galvanise international support in the fight against climate change when he addresses the UN, 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.

· Thousands march in global climate rallies

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.

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.

On Sunday, celebrities, political leaders and the masses rallied in New York and across the globe demanding urgent action on climate change, with organisers saying 600,000 people hit the streets.