A new study has found that the number of people living on land at risk of coastal flooding could be three times greater than the number previously thought.
To come up with these new estimates, scientists from Climate Central, a Princeton-based climate science and news organisation, used a new digital model to more accurately measure global ground elevations.
Lead author Dr Scott Kulp said: "These assessments show the potential of climate change to reshape cities, economies, coastlines, and entire global regions within our lifetimes.
"As the tide-line rises higher than the ground people call home, nations will increasingly confront questions about whether, how much, and how long coastal defences can protect them."
The study says that by 2050, 150 million people could find themselves living on land permanently below the high tide mark.
And 300 million of us could be living in places affected by coastal flooding at least once a year, up from the old estimate of 79 million — and that’s even if we reduce carbon emissions in line with the Paris agreement.
It could be much worse by the end of the century if emissions remain unchecked — with rising seas threatening as many as 640 million people.
The report found that the problem is particularly acute in Asia, with China, Bangladesh, India and Vietnam due to be worst affected.
In China, for example, previous data suggested that 29 million people live in areas that will suffer regular coastal flooding by 2050.
But the new, more accurate model created by Climate Central found that even with moderate carbon reductions, the figure is actually 93 million people.
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The difference between the two numbers is because the ground elevation data typically relied upon to work out coastal flooding risk in many parts of the world only measures elevations closest to the sky, like treetops and roofs, and doesn’t distinguish between these things and the ground.
As a result Climate Central scientists have calculated that the old data set has been over estimating coastal elevations by up to 13ft in in urban areas, indicating "false safety" from floods.
The report authors say their new precision model reduces these errors to approximately four inches on average.
Climate Central chief scientist and report co-author Dr Benjamin Strauss said: "For all of the critical research that’s been done on climate change and sea level projections, it turns out that for most of the global coast we didn’t know the height of the ground beneath our feet.
"Our data improves the picture, but there is still a great need for governments and aerospace companies to produce and release more accurate elevation data. Lives and livelihoods depend on it."
Dr Strauss told Sky News that he is "most concerned" when he looks at the political pressures and instability caused by refugees and migrants coming from Syria and Africa within the last five years, but that these numbers are "a drop in the bucket" compared to the number of climate refugees that will be created by sea level rises without careful planning, defences and a massive reduction in carbon emissions.
He also said that the new predictions mean that many more people in coastal communities may be faced with a stark choice about how to spend resources: defend what already exists, or make a planned retreat from the ocean.