Sea levels are rising faster than scientists had predicted, according to a landmark UN report that laid bare the severe risk to coastal cities and low-lying islands from climate change and the parlous state of the world’s oceans.

The report from the Intergovernmental Panel on Climate Change, a gold standard of scientific research, outlined the threat to hundreds of millions of people from the acceleration in the rate at which sea levels are rising, caused by a combination of melting ice in polar regions such as Greenland and Antarctica and the expansion of the oceans as the water warms.

The researchers warned that extreme floods, the likes of which have historically only occurred once per century, were likely to happen at least once per year by 2050 in many regions, especially the tropics, even if global warming is limited to 1.5C.