Millions face long-term coastal flooding risk in UK without climate action, scientists warn

A ‘reasonable worst-case scenario’ suggests need for large-scale movement of populations away from reshaped coast

Up to 13 million people in the UK face the long-term risk of coastal flooding due to the climate crisis, scientists have warned, with a “reasonable worst-case scenario” suggesting the need for the large-scale movement of populations away from a dramatically reshaped coast.

Even if today’s global pledges to cut carbon pollution are met, about 1.4 million more people will be exposed to coastal floods in 2200 and 1.7 million in 2300 due to the sea level rise driven by melting ice caps and warming oceans.

While this is far in the future, action today to cut emissions and plan future settlements and flood defences could prevent such leaps in flood risk becoming inevitable, the experts said. Keeping within the Paris agreement targets would cut the number of people exposed in 2300 by 1 million, they said.

Sea level has risen by about 20cm around the UK in the last century and is accelerating. A further 40cm to 60cm by 2100 is already baked in, meaning about half a million more people will be at risk of their homes being flooded, on top of the 2.5 million already in danger near the coasts. Lincolnshire and the Humber estuary are most in danger.

However, scientists are concerned that the gradual rise in sea levels seen so far could change rapidly if ice sheets start a runaway collapse into the oceans, instead of just melting slowly in place. In this scenario, the UK could suffer 15 metres of sea level rise by 2300, swamping large parts of London and many other places, the researchers found.

“[Planners] who only consider changes over the coming century may have a false impression of the true risk landscape given the potential for post-2100 acceleration of sea level rise,” the researchers concluded in their study published in the journal Nature Communications . “It is inevitable that a combination of additional or enhanced flood defences and managed retreat will be necessary to mitigate against post-2100 flood risk.”

Prof Matt Palmer at the University of Bristol, who led the research, said: “The oceans and ice-covered parts of the world respond very slowly to global warming, which makes sea level rise the ‘sleeping giant’ of climate change. The result is that sea-level rise is locked-in for centuries to come.”

Dr Rob Larter, at the British Antarctic Survey and not involved in the study, said it was a sobering analysis: “It shows how the UK is likely to have to adapt to several metres of sea level rise over coming centuries. The higher impact [scenarios] presented in this study need to be considered as genuine possibilities rather than unlikely scare stories.”

The research is the first to quantify the number of UK people at threat from coastal flooding under long-term sea level rise. It combined sea level rise projections for the UK with a detailed flood model developed by the Bristol company Fathom . Sea level rise is greater in England and Wales than in Scotland and Northern Ireland as the latter countries were pushed down during the last ice age and are still slowly rebounding.

The study did not factor in greater surges from storms supercharged by global heating or future changes in population. It also did not consider future changes to flood defences, which are highly uncertain, but instead set out the level of likely threat in different scenarios.

Dr Joanne Williams, at the National Oceanography Centre in Southampton, said: “It is useful to consider [worst-case scenarios], because it shows how expensive and challenging it will be if we do not act on climate, with very large areas at new risk. Upgrading existing flood defence lines to the levels required by these high-end scenarios would be extremely challenging.”

Coastal flooding is just one type of flood risk in the UK. River and flash flooding already affect more people and are worsening as the warming climate leads to more intense rainfall.