Governments can no longer hide from the devastating consequences of wild weather and rising seas, and must dig deeper into their pockets to curb and repair the damage, developing nations said ahead of a key U.N. climate change conference.
They urged leaders at the Dec. 2-14 talks in Poland to commit to moving faster by 2020 to cut planet-warming emissions, and to boost financial help for poor nations struggling to cope with worsening droughts, floods, storms and heatwaves.
Gebru Jember Endalew, chair of the Least Developed Countries (LDC) group at the talks, said international cooperation was "the only way to address the global threat of climate change".
"Trillions of dollars in climate finance (are) needed to cover the costs of adapting to climate change impacts, coping with loss and damage, and pursuing clean development pathways to avoid emissions," he said in a statement before the meeting.
The African, Caribbean and Pacific Group of States said on Thursday 59 of its member nations needed about $2.3 trillion to carry out their national climate action plans.
The LDC group said in a briefing note that developing countries overall will require more than $4 trillion to put into practice the plans they have submitted to the United Nations as part of the Paris Agreement on climate change.
Over the next two weeks, officials from about 195 countries are tasked with agreeing on guidelines to implement the 2015 deal to keep global warming in check.
As part of that, "clear rules" are needed on the provision of "adequate and predictable climate finance" to make intended steps to tackle climate change a reality, Endalew said.
Delays in cutting emissions and adapting to changes already underway will mean higher costs down the road, as impacts become more severe, experts say.
"The longer poor countries have to wait, the larger the cost will become," Endalew warned.
How to find and fairly distribute enough funding for frontline nations to stay safe in a warming world and to develop cleanly remains a hot topic at the U.N. talks.
Wealthy governments are under pressure to meet a pledge to raise $100 billion every year for that purpose from 2020.
The Organisation for Economic Co-operation and Development (OECD) said on Thursday climate finance provided by rich states to developing nations totalled $56.7 billion in 2017, up 17 percent from $48.5 billion in 2016.
It did not give an update on how much private finance has been mobilised by governments toward the $100 billion goals.
Analysts said the OECD number and a new U.N. assessment suggested donors were broadly on track to keep their promise, made in 2009, although exactly what should be counted towards the goal remains controversial.
Joe Thwaites, a sustainable finance researcher with the World Resources Institute (WRI), said the 2017 OECD estimate had assuaged fears government funding might "fall off a cliff edge" after U.S. President Donald Trump took office and vowed to slam the brakes on international contributions.
But experts expressed concern at the small amounts allocated for coping with climate change impacts - barely a quarter of the total spending - compared with far more generous funding for boosting renewable energy and energy efficiency.
And they warned the high proportion of loans offered relative to grants could leave poor countries in debt.
Recent U.N. and other reports have made it clear "there is no question we are dealing with serious (climate change) impacts, and there is a huge, huge need for adaptation finance", said WRI researcher Niranjali Amerasinghe.
But Li Shuo, climate and energy policy officer at Greenpeace China, said negotiators at the Poland talks would tangle over proposed rules to improve the predictability of donor funding.
Even European countries - which have been keener to deliver climate finance - are reluctant to sign up to making future projections of their own funding commitments under the Paris "rulebook", said Jens Mattias Clausen, climate change advisor with Greenpeace Nordic.
Andrew Norton, director of the London-based International Institute for Environment and Development, urged wealthy countries to demonstrate at the talk show they planned to deliver the $100 billion per year, and how they would significantly increase that amount from 2025, as agreed in the Paris accord.
"This is essential to enabling developing countries to build the skills, institutions and systems that are fundamental to their developing and even thriving in the face of climate change," he said in a statement.
(With inputs from agencies.)