The co-chairs of the United Nations advisory group charged with finding $100 billion a year to help developing countries meet the challenges of climate change said Tuesday that they will present their final report in October, ahead of the U.N. climate conference in Mexico.

The 21 member high-level advisory panel headed by Ethiopian Prime Minister Meles Zenawi and his Norwegian counterpart Jens Stoltenberg wrapped up its second meeting on Tuesday in New York.

The panel is seeking ways to come up with $100 billion per year by 2020 to help developing countries adapt to and mitigate the effects of global warming.  At the U.N. climate conference in Copenhagen in December, world leaders also promised developing countries an additional $30 billion between now and 2012.

At a news conference following the group's New York meeting, U.N. Secretary-General Ban Ki-moon said the panel is looking to identify the sources of this longer-term financing. "These sources must be economically sound and politically viable," he said.

Norwegian Prime Minister Stoltenberg said there are several possible sources of financing, but he agreed with Mr. Ban that a key challenge for the panel is to find ones that are politically and practically feasible.

"I think that is the main issue for our group - to try to make some progress in making the many different sources of finance into reality and giving valuable input to the negotiators, to the governments, so they can agree on something which is going to become reality and which can provide us with the necessary financial flows," he said.

The panel is expected to meet again in October in Addis Ababa to finalize its recommendations for the secretary-general ahead of the November climate meeting in Cancun.

The funding is expected to come from the public and private sectors.  Some possibilities that have been discussed are government grants, private sector lending and new taxes on the shipping and aviation industries.

Small island nations are among the most vulnerable to the effects of climate change.  A group of 11 Pacific island countries issued a statement on Tuesday expressing their frustration over the lack of progress in mobilizing the needed funding.  They argue that $100 billion a year is "grossly inadequate" and say industrialized countries have a responsibility to provide a remedy for the damage they have caused.

In addition to the prime ministers of Norway and Ethiopia, the advisory panel includes the president of Guyana, ministers from Britain, France, Mexico, Singapore and South Africa as well as billionaire businessman George Soros and White House economic advisor Lawrence Summers.