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Coastal Flooding ‘May Cost $100,000 Billion a Year by 2100’

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Posted on Feb 13, 2014

Lee Cannon (CC BY-SA 2.0)

By Tim Radford, Climate News Network

This piece first appeared at Climate News Network.

LONDON—If global warming continues on its present ominous path, and if no significant adaptation measures are launched, then coastal flooding could be costing the planet’s economies $100,000 billion a year by 2100.

And perhaps 5% of the people on the planet – up to 600 million people – could be hit by coastal flooding by the end of the century, according to new research in the Proceedings of the National Academy of Sciences.

Jochen Hinkel from the Global Climate Forum in Berlin and colleagues have compiled, for the first time, global simulation results on future flood damage to buildings and infrastructure on the world’s coastal flood plains.

They expect drastic increases in economic damage because, as sea levels rise with the decades, so will population and investment: there will be more people with more to lose.

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Right now, coastal floods and storm surge damage cost the world between $10 billion a year and $40 billion. But as the megacities grow – think of Lagos, or Shanghai, or Manila – more people will be at risk, and, among them, greater than ever numbers of the poorest.

“If we ignore this problem, the consequences will be dramatic,” says Hinkel. “Countries need to take action and invest in coastal protection measures, such as building or raising dykes, amongst other options.”

Provoking a response

And his co-author Robert Nicholls from the University of Southampton warns: “If we ignore sea level rise, flood damages will progressively rise and presently good defences will be degraded and ultimately overwhelmed, hence we must start to adapt now.”

All such projections involve assumptions about the future that cannot be tested, so the authors spread their bets: they considered a range of scenarios involving crude population growth, levels of economic growth with time, and a series of predictions of sea level rise, as icecaps and glaciers melt, and as the oceans warm and expand according to predictable physical laws.

What they could not predict – because such things require political decisions of the kind they hope to provoke with their forecasts – would be the civic and political responses in the next eight decades as storms become more violent and floods more frequent.

Nor did they try to incorporate the natural consequences of human settlement: how much subsidence, for instance, would occur as humans pumped groundwater from aquifers or quarried strata for building material, all things that would lower the levels of the land already at risk from invasion by the sea.

But their predictions, while alarming, are only reinforcements of earlier investigation. In August a World Bank team calculated that floods would be routinely costing coastal cities $1 trillion a year by 2050.

In July last year, a team from Stanford University in California looked at the challenge of building sea defences and proposed that by far the most efficient solutions would all be natural: dune systems, mangrove forests, reefs, water meadows, kelp forests and natural estuary ecosystems provided the best protection for many people in many circumstances.

And in December scientists from the University of Massachusetts considered the devastation wreaked on New York and other American cities by Superstorm Sandy in October 2012 and warned that such things could happen again and that, once again, natural systems might provide the most efficient buffers against the buffetings of the weather.

Huge losses

The PNAS authors consider for the purpose of their argument only the increasing costs of either maintaining sea barriers such as dykes, or raising them.

By 2100, global average sea level rise could be as low as 25 cms, or as high as 123 cms; between 0.2% and 4.6% of the world’s population could be affected by flooding each year; and losses could be as low as 0.3% or as high as 9.3% of global gross domestic product.

It doesn’t matter very much whether by the end of the century the losses hit the low end of these projections, or the high. They will always be huge. “Damages of this magnitude are very unlikely to be tolerated by society and adaptation will be widespread”, the authors warn.

And there will be tracts of land that no dykes could ever save from the rising waters. The poorest countries are in any case unlikely to be able to meet the costs of sustained protection from the sea.

“If we do not reduce greenhouse gases swiftly and substantially, some regions will have to seriously consider relocating significant numbers of people in the longer run”, says Hinkel. He and his co-authors want to see some significant long-term thinking.

His colleague Professor Nicholls adds: “This long-term perspective is however a challenge to bring about, as coastal development tends to be dominated by short-term interests of, for example, real estate and tourism companies, which prefer to build directly on the waterfront with little thought about the future.”


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