A critical meltdown of ice sheets and severe sea level rise could be inevitable because of climate change, scientists are preparing to warn their governments.

New studies of Greenland and Antarctica have forced a the IPCC to conclude there is a 50% chance that widespread ice sheet loss “may no longer be avoided”.

Such melting would raise sea levels by four to six metres. It would cause “major changes in coastline and inundation of low-lying areas” and require “costly and challenging” efforts to move millions of people and infrastructure from vulnerable areas.

Areas such as the Maldives would be swamped and low-lying countries such as the Netherlands and Bangladesh, as well as coastal cities including London, New York and Tokyo, would face critical flooding.