The cost of adapting to climate change is between five and 10 times higher than the money currently being spent, research has found, despite funding hitting 79.6 billion dollars (£58 billion) in 2019.
The UN Environment Programme (Unep) warned that on the current trajectory, the cost of adapting to extreme weather could be between 140 billion and 300 billion dollars (£102 billion to £220 billion) for developed countries by 2030.
This figure rises to between 280 billion and 500 billion dollars (£205 billion to £367 billion) for developing countries by the middle of the century.
In the Adaptation Gap Report: The Gathering Storm, Unep warned that even if warming is limited to 1.5C the impacts of climate change, such as wildfires and floods, will last for decades.
Ahead of Cop26, the pledges of governments around the world put the Earth on a path for 2.7C of warming.
Unep said that despite growing urgency, the flow of finance directed at adaptation “seems to be levelling off”.
Adaptation should reduce loss and damage caused by extreme weather, Unep said, particularly in the second half of the 21st century when the consequences of climate change will be inescapable.
But it added that it found a concerning lack of evidence of risk reduction as a result of existing adaptation strategies.
The report also found that international governments were letting the opportunity to reset course after the pandemic pass them by.
Around 16.7 trillion dollars (£12.2 trillion) of fiscal stimulus has been deployed globally, but only a fraction was directed towards climate change adaptation strategies.
In a sample of 66 countries, less than a third had used post-pandemic funding to address climate risk.
The report found that the pandemic had placed nations in a double bind, as falling revenues limit government spending, while the cost of adaptation rises rapidly as climate change accelerates.
Unep said countries must raise their ambitions for adaptation measures to stop the gap between the pace of infrastructure development and climate change risks from widening.
It said action needs to be rapidly scaled up, particularly in developing countries.
But elsewhere it found that while cash flows and the pace of change may be lagging, progress was still being made, particularly among the least developed nations.
Around 79% of countries now have at least one national-level adaptation measure in place, in strategy, policy or law.
About 9% of the countries that do not have a plan are in the process of developing one, the study found.
Unep’s research found that around 20% of projects focus on adaptation for agriculture, while 20% are protecting ecosystems, and two in 10 focus on water supply or other infrastructure.
But it raised concern about the low rate of monitoring of the efficacy of new systems, with only 26% of countries having an evaluation process.
Inger Andersen, executive director of Unep, said: “As the world looks to step up efforts to cut greenhouse gas emissions – efforts that are still not anywhere strong enough – it must also dramatically up its game to adapt to climate change.
“Even if we were to turn off the tap on greenhouse gas emissions today, the impacts of climate change would be with us for many decades to come.
“We need a step change in adaptation ambition for funding and implementation to significantly reduce damages and losses from climate change. And we need it now.”
Wealthy nations are not expected to deliver the promised 100 billion dollars (£73 billion) in climate finance to developing countries until 2023, three years later than planned.
Research by the Organisation for Economic Co-operation and Development (OECD) found climate finance provided and mobilised by developed countries was just short of 80 billion dollars in 2019.
The majority came from public sources, with private finance flows lagging behind despite the fact the majority of public money was loans rather than grants.
It also found far more money went towards funding emissions cuts than on adaptation strategies, despite calls for funding to be divided equally between mitigation and adaptation.
Delivering on finance promises is seen as one of the key tests of the success of Cop26.
Prof Daniela Schmidt, professor in palaeobiology at the University of Bristol, said: “There are many plans for adaptation, but much less action.
“While many small-scale examples give an indication of the power of well designed and implemented adaptation, we lack urgently needed knowledge about what works where, and for whom and which approaches are most effective.
“Making decisions without this knowledge sets us on adaptation pathways which may have unintended consequences.
“The lack of understanding results in our inability to upscale and transfer successful adaptation examples to other regions and systems.”