Major cities such as London, Bangkok, Shanghai and Houston could sink amid rising sea levels, says a new report from Christian Aid.
The new document highlights major coastal cities are at risk of being submerged, with sea levels expected to rise by more than 40cm (16in) if global warming is not limited to 1.5C.
The report, released on Thursday, comes ahead of multinational meeting to finalise a report on the impacts of global temperature rises of 1.5C above pre-industrial levels – and what is needed to prevent further warming.
It states that climate change could act as a “threat multiplier” to existing problems such as sinking ground and subsidence, water extraction and bad planning.
The study says London’s sinking problem is largely a vestige of the last ice age when glaciers that weighed Scotland down and lifted up the south – much like a see-saw – melted and reversed the effect.
The UK capital is also increasingly vulnerable to sea level rises, with the city having to use its key primary flood defence, the Thames Barrier, more frequently.
In 1984, when the barrier opened, its annual use was predicted to be two to three times a year.
It now said the flood barrier, which keeps water levels at bay, is now being used around six or seven times a year.
Cities such Houston, Texas are vulnerable to flooding and subsidence due to extracting groundwater for its population and oil and gas supplies. The report also said sea level rises and storm surges will only exacerbate the problem.
Bangkok’s government published a report three years ago warning the city could be underwater in the next 15 years, sinking due to water extraction and heavy buildings pressing into the sediment.
Shanghai is another city where groundwater use has caused subsidence and where heavy buildings are weighing down on the sediment it is built on, though it has taken strong measures to tackle these problems.
Manila in the Philippines; Jakarta, Indonesia; Lagos, Nigeria, and Dhaka in Bangladesh are all also threatened by problems such as subsidence, groundwater extraction, a lack of adequate drainage, the weight of buildings and the loss of natural flood protection including mangroves.
Report author Dr Kat Kramer, Christian Aid’s global climate head, said: “We’re starting to see what happens when climate change acts as a threat multiplier, compounding poor development decisions.
“We’re already at around 1C of warming and we are getting a picture of what happens if we exceed 1.5C.
“Worryingly, the world is currently on track for more than 3C of warming, which would have disastrous consequences for the millions of people living in these coastal cities.”
Mrs Kramer urged governments to heed the findings of the forthcoming report.
She advised they increase their pledges for climate action, in order to curb temperature rises to below 1.5C.