In just 30 years, a whopping 340 million people living on the coast can expect annual flooding or permanent inundation, according to a grim new report released by scientists.

By 2050, the worlds coastlines will look incredibly different with 70 per cent of the projected 340 million at risk living in China, Bangladesh, India, Vietnam, Indonesia and Thailand. The 340 million projection is well above the previous estimate of 80 million.

The report, from Climate Central and published in the journal Nature Communications, paints a harrowing picture for most of Asia as sea levels are projected to rise between 0.6m and 2.1m.

By 2100, with the stability of the Antarctic ice sheet already worsening, as many as 640 million people could be threatened by rising sea levels.

Using a form of artificial intelligence known as neural networks, the new research corrects ground elevation data that has up to now vastly underestimated the extent to which coastal zones are subject to flooding during high tide or major storms.

Sea-level projections have not changed, co-author Ben Strauss, chief scientist and CEO of Climate Central, said.

But when we use our new elevation data, we find far more people living in vulnerable areas that we previously understood.

Previous data on rising sea levels made the crisis seem manageable but as Mr Strauss said, governments must act on these new maps to avoid economic and humanitarian catastrophe.

With the global population is set to increase two billion by 2050 and another billion by 2100 mostly in coastal megacities even greater numbers of people will be forced to adapt or move out of harms way.

Already today, there are more than 100 million people living below high tide levels, the study found. Some are protected by dikes and levees, most are not.

Chinas low cities are particularly at risk including Shanghai and Tianjin. Hong Kong also faces severe flooding risks by 2050 while the report projects much of the southern part of Vietnam could also be wiped out.

Ho Chi Minh City is in the south of Vietnam, the countrys largest and most populated city.

The numbers at risk of an annual flood by 2050 in Bangladesh also increased more than eightfold in the study.

But it isnt just Asia that will face inundation by 2050.

Parts of Brazil and the UK could see permanent land loss by 2100. The report estimates more than 3.6 million Brits could be at risk of annual flooding by 2050.

If our findings stand, coastal communities worldwide must prepare themselves for much more difficult futures than may be currently anticipated, the study warned.

Recent work has suggested that, even in the US, sea-level rise this century may induce large-scale migration away from unprotected coastlines, redistributing population density across the country and putting great pressure on inland areas.

The report will leave millions of people around the world questioning how long they want to live on the coast, lead author and Climate Central scientist Scott Kulp said.

Climate change has the potential to reshape cities, economies, coastlines and entire global regions within our lifetime, Mr Kulp said.

As the tideline 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.

Several factors conspire to threaten populations living within a few metres of sea level.

One is the expansion of water as it warms and, more recently, ice sheets atop Greenland and Antarctica that have shed more than 430 billion tonnes per year over the last decade.

Since 2006, the waterline has gone up nearly four millimetres a year, a pace that could increase 100-fold going into the 22nd century if carbon emissions continue unabated, the UN Intergovernmental Panel for Climate Change (IPCC) warned in a major report last month.

Major storms that until recently occurred once a century will, by 2050, happen on average once a year in many places, especially in the tropics, the IPCC report found.

Annual coastal flood damages are projected to increase 100 to 1,000-fold by 2100, it said.

Finally, many of the one billion people living at less than nine metres above sea level today are in urban areas literally sinking under their own weight.

With AAP

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