Prime Minister Tony Abbott has rejected a call by fellow Commonwealth leaders to set up a new climate fund to help poor nations.

Mr Abbott also found himself at odds with British prime minister David Cameron over his strong defence of Sri Lanka's efforts to address alleged human rights abuses and war crimes.

As the Commonwealth Heads of Government Meeting wrapped up in Colombo on Sunday, Mr Abbott joined Canada in rejecting a decision by the summit to establish a green capital fund to help small island states and poor African countries address the effects of global warming.

The final agreement noted that "Australia and Canada ... indicated that they could not support a green capital fund at this time".

A Commonwealth expert group also called for new ways to access existing international funds to address climate change.

Small state leaders pleaded with their colleagues to urgently address global warming, which threatens their long term existence.

New Zealand Prime Minister John Key, who agreed to the fund in principle, said Tony Abbott and the Canadian delegate had said they "can't agree to fund their contribution".

"Australia is going to have to establish as a government how it will approach these international issues," Mr Key said.

"We are taking the middle path but the right path."

New Zealand has an emissions trading scheme but the Abbott government is in the process of repealing the former Labor government's scheme.

With Sri Lanka's human rights record a key point of discussion, Mr Abbott urged Commonwealth leaders to let Sri Lanka itself deal with the fallout from 30 years of civil war and declared the two nations to be "good mates".

The UN says as many as 40,000 civilians may have been killed in the final stages of the war in 2009 when Tamil Tigers rebels were crushed by government troops.

Mr Cameron used the summit to put an ultimatum to President Mahinda Rajapaksa to properly investigate claims of war crimes by March or face a UN inquiry.

Mr Rajapaksa has denied civilians were killed and told Mr Abbott in a bilateral meeting Sri Lanka was addressing human rights concerns through the Lessons Learnt and Reconciliation Commission and other inquiries.

"The important thing is to work constructively with Sri Lanka to try to ensure all of the people of Sri Lanka have the best possible future," Mr Abbott said.

Mr Rajapaksa praised Mr Abbott's practical approach.

While not directly addressing Sri Lanka, the leaders used the final communique to reaffirm their commitment to democracy, the rule of law and human rights.

Mr Abbott met some villagers from Sri Lanka's northern province at Australia's high commission in Colombo, just before he left for Canberra.

"What has impressed me about the people of Sri Lanka over the past few days is their potential to really lift this country quickly into a much better condition... and efforts that they've made to put behind them some of the animosities of the past and reach out to one another in a spirit of friendship and national harmony."

Malta will host the 2015 summit, while Vanuatu and Malaysia will host the subsequent meetings.