Other experts echoed that but said the administration needs to think even more broadly. Michael Liebreich, chief executive of Bloomberg New Energy Finance, said he thinks the best way to generate fresh ideas that will actually work is to have the big banks be part of the discussion. Moreover, he said, the focus should be on understanding what companies need to provide financial backing to potentially risky projects in developing countries, rather than on just raising the cash.
"Who will go? You can almost measure the success of the thing by who is there and who is not there. Until Goldman Sachs is sitting around the table, then you haven't created an investment that is going to be at scale," Liebreich said.
"There's a lot of thinking on climate finance that focuses on the supply of money, but actually you need to think about the demand," including what the money should be used for and why the private sector isn't already doing a particular project. "What the private sector needs to do is surgically fill gaps rather than fill a pool," Liebreich said.
Barbara Buchner, head of the Climate Policy Institute Europe, who has written some of the leading policy papers on climate finance, noted that the $364 billion that went to clean energy activity globally last year is a pittance compared to the $1 trillion that the International Energy Institute says is needed annually. That, she noted, doesn't even take adaptation into consideration.
Moving nations out of 'comfort zones'
The scale of the need, combined with the unlikelihood of big increases in taxpayer-funded aid from the United States or Europe, she said, makes private-sector participation all the more important. From feed-in tariffs to risk guarantees, she said, governments need to talk out the different types of policy incentives that could unlock private capital in various parts of the world.
"There is a need to make progress in this area, and it is one area where we can make progress. But there's no one solution fits all," Buchner said. She called the proposed meeting "a positive signal that there are some policymakers that are going to drive the agenda."
Some activists, though, said they are concerned that the United States will focus entirely on private-sector funding and will once again sidestep ways of raising public money, including from "innovative sources," like a tax on bunker fuels or airline emissions.
"This needs to not just be a perceived conversation where everyone is trying to duck the issues that are complicated to them," said Jake Schmidt, international policy director for the Natural Resources Defense Council. While developing countries will need to move away from some ideological positions that demand public dollars as a form of retribution for climate damages, he said, the United States, in turn, will also have to move out of its comfort zone in order for any finance meeting to be productive.
"The U.S. needs to be prepared to have a discussion about what the public finance component looks like. What innovative finance measures would work for them?" Schmidt said.
Athena Ballesteros, who leads work on climate finance for the World Resources Institute think tank, said, "If this meeting will help contribute to the goal of coordinating countries plans and actions to mobilize the $100 billion pledge, that would be most welcome, and part of the conversation is to find innovative sources of finance that would complement the scarce public resources being made available."
What that conversation will look like remains unclear. Metcalf, the Tufts University professor, said he does not believe the United States or other governments should even be held to a minimum level of public funding to build up the $100 billion.