New data shows more than three times as many people will be at risk of flooding from higher tides later this century than previously estimated.
By 2050, rising seas could push peak high tides above land currently home to at least 300 million people, mostly in Asia. This is a huge increase from previous projections of 79 million people.
According to the research, roughly 110 million people already live below the average high-tide line, where they are to some degree protected by existing coastal defences like sea walls. By 2100, land that is now home to 200 million people, including 43 million in China, could sit below the average high-tide level.
Those forecasts are based on humanity reducing emssions in line with the 2015 Paris Agreement to keep temperature rise to 2C. They were made with a new digital elevation model by scientists at US not-for-profit Climate Central that found many of the world’s coastlines to be far lower than previously calculated.
Old estimates using satellite data had measured elevation from tree canopies and rooftops rather than the ground. The scientists used machine-learning to correct errors in this historical data, extrapolating from more accurate measurements achieved in some western countries. On average, coastal elevation had been overestimated by 2m and more than 4m in high-density urban areas. The elevations from the new model are much more accurate, with average error reduced to less than 7cm.
Driven by global warming, sea levels rose by 11-16cm in the 20th century. Even with sharp cuts to carbon emissions, they are projected to rise another 50cm this century, and under higher emissions scenarios, this figure could exceed 2m. Predicting where rises will occur is crucially important for planning and adaptive measures such as flood defences or relocation.
The interactive maps below are derived from Climate Central’s world map. They make clear the scale of the difference between the legacy data and their new elevation model, known as CoastalDEM. They show annual flood projections for 2050 based on emissions cuts in line with the Paris Agreement.