Gordon Brown and Ban Ki-moon are
attending the summit in Trinidad
Commonwealth leaders have backed a multi-billion-dollar plan to help developing nations to deal with climate change and cut greenhouse gases.
The fund, proposed by UK and French leaders at the Commonwealth summit on Friday, would start next year and build to $10bn annually by 2012.
Many Commonwealth members are island states threatened by rising sea levels.
Leaders also called for the strongest possible outcome at next month's climate change summit in Copenhagen.
But they accepted that a 'legally binding agreement' might have to wait to 2010.
Commonwealth leaders "welcomed the initiative to establish, as part of a comprehensive agreement, a Copenhagen Launch Fund starting in 2010 and building to a level of resources of $10 billion annually by 2012," a statement in Trinidad on Saturday said.
It added that "fast start funding" for adaptation should be focused on the most vulnerable countries.
"We also recognise the need for further, specified and comparable funding streams, to assist the poorest and most vulnerable countries, to cope with, and adapt to the adverse impacts of climate change. We recognise that funding will be scaled up beyond 2012."
UK Prime Minister Gordon Brown said half the $10bn fund should go towards helping developing nations reduce their greenhouse gas emissions and the other half towards helping them adapt to climate change.
The first cash would be made available next year, he said, before any emissions deal could take effect.
Commonwealth leaders met days after pledges by the US and China to limit their greenhouse gas emissions, amid concerns that December's Copenhagen meeting on climate change could fail to agree substantial cuts.
Australian Prime Minister Kevin Rudd told a news conference in Trinidad on Saturday that the Commonwealth - representing a third of the world's population - believed "the time for action on climate change has come."
"The clock is ticking to Copenhagen. We've achieved one further step, significant step forward with this communique and we believe the political goodwill and resolve exists to secure a comprehensive agreement at Copenhagen."
Speaking earlier at the summit, UN Secretary General Ban Ki-moon said he believed an agreement was in sight, with recent moves by some countries a positive step to cutting emissions.
The head of the UN's panel of climate experts, Rajendra Pachauri, said he was now very optimistic a deal could be reached in Copenhagen.