As the United States officially re-enters the Paris climate accord on Friday, expectations are rising that Washington will step up funding to help poor countries adopt clean energy and adapt to more extreme weather as the planet warms.
Under climate-change sceptic Donald Trump, the US government did provide finance for things like building solar power systems in Africa and protecting people from storms and floods in Asia, as part of its international development aid.
But Trump pulled out of the 2015 Paris Agreement and refused to deliver two-thirds of a $3-billion pledge made by his predecessor to the Green Climate Fund, set up under UN climate talks to help developing nations tackle global warming.
Environmental groups this week delivered a petition signed by more than 50,000 US residents, urging the administration under new US President Joe Biden to do its "fair share" in cutting emissions and providing climate finance.
Brandon Wu, director of policy for ActionAid USA, said that, as the biggest long-term contributor to climate-heating emissions, the United States had a moral and legal responsibility to help vulnerable communities now bearing the brunt of extreme weather and rising seas in a warming world.
"Doing our fair share of climate action means addressing the injustices we have visited on those communities – starting with providing real financial support for just and equitable climate action in developing countries," he said in a statement.
Earlier this month, ActionAid and 45 other development agencies and green groups issued an open letter calling on Biden's government to pledge and support appropriation of at least $8 billion for the Green Climate Fund.
That amount includes the $2 billion owed plus a doubling of the initial US pledge for the coming three years, in line with commitments by other wealthy governments such as France and Germany.
The groups also said the US government should provide $400 million over four years to the smaller Adaptation Fund, another UN-linked fund that boosts climate resilience in poor nations. That would mark a first-ever US contribution to the fund.
CLIMATE FINANCE PLAN
Hopes are high that Biden's government will make up for lost time after US climate envoy John Kerry promised in January his country would "make good" on its climate finance promise, without specifying when or how.
Most experts took that to mean the United States would deliver the money Trump withheld from the Green Climate Fund.
In an executive order on climate change, signed on Jan. 27, Biden also instructed government departments to craft a climate finance plan to help developing countries reduce emissions, protect critical ecosystems and build resilience to climate change impacts.
The plan is due to be submitted by the end of April, but experts hope it will land before a leaders' climate summit Biden has convened for major-emitting nations on April 22.
Joe Thwaites, a sustainable finance associate at the Washington-based World Resources Institute, said commitments to specific climate funds could be announced before or in the plan, but it should also give a broader view of how the United States intends to approach climate finance over Biden's term.
That would help other countries know what to expect in terms of levels of financial support and where it will go, he added.
"That makes it much easier to plan," he said - both for those seeking to receive the money and for donors working out where best to add value with their own assistance.
'LAGGING BADLY'
A lack of climate finance, particularly that reaching the most vulnerable countries, has been a big sticking point in UN climate negotiations.
In December, UN Secretary-General Antonio Guterres warned rich governments were "lagging badly" on a longstanding pledge to channel $100 billion a year in funding from 2020 onwards to help poorer nations develop cleanly and adapt to climate change.
He pointed to a new report by climate finance experts estimating that the $100-billion promise would not be kept by the deadline.
Due to a lag in how governments report international climate funding, the total provided in 2020 may not be known until early 2022.
The latest figures, released by the Organisation for Economic Co-operation and Development (OECD) last November, said climate finance for developing states rose by 11% to $79 billion in 2018 - about $20 billion short of the flagship 2020 goal.
And in January, the Climate Policy Initiative think-tank said finance for adaptation - already deemed highly inadequate - was likely to have dropped in 2020 as the pandemic hit budgets.
The figures collated annually by the OECD have been criticised for including loans, which must be paid back, and donor aid given for broader development projects not fully dedicated to tackling climate change.
An international team of researchers wrote in Nature Climate Change on Thursday that the ambiguity of the original $100-billion promise and "questionable claims" by donors about their contributions "make it impossible to know if developed nations have delivered".
They called for negotiations on a new climate finance goal- starting at the COP26 UN climate conference in November - to set clear rules on what can be counted.
The new goal, due to kick in from 2025, should be decided in a way that is accountable and builds trust, as well as being based on "realistic assessments of developing countries' needs".
In addition, "real plans" should be drawn up to meet the new funding targets, such as tapping innovative finance like levies on international airline passengers and shipping fuels, they said.
Co-author Romain Weikmans, of Belgium's Université Libre de Bruxelles, said other changes for 2025 could include setting separate goals to fund climate adaptation or to channel more money to the poorest nations and threatened small-island states.
He also suggested an independent body, like the Intergovernmental Panel on Climate Change, could be tasked with defining new climate finance guidelines, to depoliticise the process.
"There needs, absolutely, to be more progress on the way we account for climate finance," he said.