France promised $1bn to a near-empty climate change fund for poor countries on Tuesday and called for the establishment of a new green economy in the first concrete result of a milestone United Nations summit.

The pledge came on a day of impassioned speeches from some 120 presidents and prime ministers – as well as a cameo by the actor and now UN ambassador Leonardo DiCaprio – telling the summit they had wasted precious time and now needed to deal urgently with climate change.

Both China and America, the world’s two biggest emitters, pledged their support for a climate deal, without offering specifics.

Chinese vice-premier Zhang Gaoli said his country’s emissions would peak “as soon as possible”, and pledged $6m to help developing countries fight climate change. Barack Obama, in a stirring address, said America would lead efforts to reach a global compact on climate change. “We are the first generation to feel the impact of climate change and the last to be able to do anything about it,” he told the summit.

David Cameron touted his government’s environmental policies. “As prime minister I pledged to lead the greenest government ever and I believe we have kept that promise,” he said.

But leaders from Africa and the Pacific islands threatened by rising seas said rich countries needed to do more.

“We must get away from the ‘wait and see who is doing what’ style of leadership before deciding what needs to be done,” said Anote Tong, the president of Kiribati, which could be drowned by rising seas.

The summit – the first such gathering of world leaders in five years – was convened to move countries towards an international agreement in Paris to fight climate change by the end of next year.

The French leader, François Hollande, said it would be impossible to reach such a deal without laying the foundations of a new green economy. “We need to define a new economy for the world.” “You can’t fight climate change without development,” he said, pledging $1bn (£600m) to a fund to help poor countries deal with climate change.

The Green Climate Fund was founded in 2010. UN officials and developing-country diplomats have said repeatedly it will not be possible to reach a deal in Paris without a significant fund for the countries which did the least to cause climate change but will bear the brunt of its effects.

Officials had been hoping to raise $10bn to $15bn by the end of the year. The German chancellor, Angela Merkel, made the first significant pledge last July, committing $1bn. South Korea, which hosts the fund, also committed $100m yesterday. But the fund remains well below its goal.

The shortfall matched the plaintive calls from presidents and prime ministers who said the United Nations and world leaders had been talking about the threat of climate change for years – without actually following through on action.

“Why today are we still so passive and so dispersed that we do not have a common strategy for the fight against climate change? Why can we not agree on a pragmatic strategy in the fight against climate change?” Ali Bongo Ondimba, th president of Gabon, told the summit.

The summit did produce other agreements – in addition to cash – but these too were relatively modest.

Some of the world’s biggest palm oil and paper producers committed to stop destructive logging by 2030, and restore a huge area of forest equivalent to the size of India.

Nigel Purvis, the chief executive of the Climate Advisers consultancy which worked to get the deal, said: “This is like if Exxon Mobil and the Koch brothers got together to cut greenhouse gas emissions.”

But Brazil – despite its critical role protecting the Amazon rain forest – said it was left out of the negotiations, and a number of campaign groups did not sign onto the agreement saying it did not go far enough to protect the rights of indigenous people who rely on the forest, or to hold the big forestry companies to account.

“I think that it’s impossible to think that you can have a global forest initiative without Brazil on board. It doesn’t make sense,” Izabella Texeira, the Brazil environment minister, told the Associated Press.