The Obama administration has delivered $7.5 billion in early climate change assistance to vulnerable countries since 2010, a new State Department report shows.

The total amount comes to nearly 25 percent of the $30 billion that wealthy countries promised to pay to poor countries in "fast start" climate aid. That three-year window of funding to protect vulnerable countries against weather-related disasters, save forests and develop clean energy closes this year, and no new payments are formally required again until 2020.

U.S. diplomats fought against developing specific new pledges to bridge the gap through 2020. But in the report, quietly released on the State Department's website Friday, the administration promised to continue delivering money and to seek other avenues of aid.

"Public finance will continue to play a critical role beyond the fast start period, particularly for adaptation. For this reason, the United States remains committed to providing public climate finance contributions in the years beyond 2012," the State Department wrote.

Still, officials added, "public finance alone will not be sufficient to address climate change. Our collective aim must be to combine a finite core of public money with targeted policies to substantially increase private flows into climate-friendly investments in both mitigation and adaptation."

Questions about accounting

The report comes as the United Nations Framework Convention on Climate Change (UNFCCC) opens its annual diplomatic negotiations in Doha, Qatar (see related story). Climate finance will be a hot topic there -- including the development of a major new mechanism called the Green Climate Fund to deliver about $100 billion annually by 2020, as well as what vulnerable countries can expect in the interim.

Experts familiar with the State Department outline say they have mixed reactions to its findings, with some questioning whether the United States has indeed lived up to its share of the global promise.

"There's no question that they increased financing in an important way over the levels that were in place before the fast-start commitment and in the previous administration," said David Waskow, the climate change program director at Oxfam America.

But, Waskow said, the levels of funding for adaptation compared with mitigating emissions remain too low. He also questioned the way in which the State Department counted some funding streams that aren't necessarily focused on climate change, like food security, health and water.

"It's extremely important, essential, that they integrate climate change into other elements of development funding, and we think they're doing good work on that front. But how it's being accounted for is not entirely clear," he said.

David Ciplet, a Brown University doctoral student who helped author a new report from the International Institute for Environment and Development (IIED) in the United Kingdom, argued that wealthy nations are not living up to their promises and the United States in particular is "still far short of providing its fair share" of the $30 billion.

What is the U.S. 'fair share'?

IIED argues that the United States should put in about 43 percent of the money, a figure it comes to by averaging responsibility for greenhouse gas emissions over the past half-century including the percentage share of each country's cumulative emissions; capability to pay based on gross domestic product; and the percentage share of the cumulative GDP of donor countries.

It's far higher than other estimates of the U.S. "fair share" for climate funding -- a calculation that is sometimes as low as 17 percent (equivalent to the amount of total aid it contributes to the Global Environment Facility) to about 20 percent (the U.S. percentage of contribution to the World Bank). But it's fuzzy math to be sure -- in no small part because the State Department has refused to formally say what it believes the U.S. share of fast-start funding should be.

Nevertheless, Ciplet said, other problems remain, including a lack of transparency as to whether funding is actually new and not merely diverted from other pots of development assistance and an imbalance toward spending money for clean energy programs while not putting enough into adaptation.

"Doha represents a huge opportunity for President Obama to demonstrate that he is serious about establishing the U.S. as a global leader on climate finance," he said. "This means offering a concrete and detailed plan to rapidly scale up wealthy country commitments in 2013 and beyond, including dramatically increasing funds to help the most vulnerable countries adapt to climate change impacts already under way and expected to worsen sharply in the coming years."

Michael Wolosin, director of research and policy for the consulting group Climate Advisers, described the overall total as "far exceeding what could be considered the U.S. fair share" by any measure. But he said he is worried about the dip in dollars over the past year and how that bodes for the future.

Between fiscal 2011 and 2012, climate finance dropped about $910 million. Nearly half that gap can be accounted for by major one-time funding to a forest program in Indonesia through the Millennium Challenge Corp. An additional $300 million of the drop was due to a decrease in development finance from U.S. export agencies. There also was a significant drop in overall climate financing over the past year.

"The fast start commitment has now come to a close, and globally there is nothing to replace it. So this slight decline from 2011 to 2012 ... could be a troubling sign," Wolosin said. "It's unclear that the U.S. or the developed world as a whole have the frameworks, the commitments and the outside drivers to really continue to ramp up the climate finance to the levels needed."

The State Department declined to comment or answer questions about its report.