Every country worldwide will be building walls to defend itself from rising seas within 90 years because the cost of flooding will be more expensive than the price of protective projects, researchers predict in a new study.

The encroaching seawater threatens to flood hundreds of millions of people every year by 2100 as homes that are already below flood heights, or will be, succumb to climbing oceans. If governments fail to take any action, the annual cost of damage stands to reach hundreds of billions of dollars, at best, and as high as $100 trillion under grimmer scenarios, according to the paper, published yesterday in the Proceedings of the National Academy of Sciences.

The bleakest outcome could result in nearly 5 percent of the world's population facing yearly floods that drain almost 10 percent from the globe's economy, the paper says. That would require a collision of severe scenarios that involve leaping ocean levels, high numbers of people living along seashores and a lack of defensive efforts.

The researchers think that the worst results are unlikely to happen, because people won't tolerate it. Instead, the group of 10 European academics predicts that the difficult decision to build expensive dike systems will grow easier in the future as the price of floods increase.

"I mean humans will do something. We're talking about massive damages if we didn't do anything," said Jochen Hinkel, a senior researcher at the Global Climate Forum and a co-author of the paper.

"Think about [Superstorm] Sandy," he added. "If that would happen every second year, that would trigger responses. It's clear we're going to see adaptation. But it's not clear how quick it will be, how successful it will be. Also we're looking at many poor countries that can't afford investments in coastal adaptation. They need financial support."

If humans build dikes, the annual cost of flooding could drop from as high as $100 trillion, in an unprotected world, to about $80 billion, Hinkel said.

The research touches on current challenges. Officials along the East Coast are considering adaptive measures like dunes, revetments, stricter building standards and expensive flood gates following Sandy's $50 billion price tag.

Paper 'shows the cost'
After Hurricane Katrina struck the Gulf Coast in 2005, the federal government undertook an ambitious effort to defend New Orleans with a system of gates and walls that cost more than $14 billion. The project wrapped up recently.

With seas almost a foot higher now than 100 years ago, those decisions are bound to become increasingly easier when compared to the cost of disasters, the researchers say. They anticipate that sea levels will climb by between 10 inches and 4 feet by 2100.

As the coastlands shrink, more people will be living there. The paper doesn't attempt to estimate the growth of coastal migration, but it uses five different scenarios of population growth that predict the world will be inhabited by between 7.2 billion and 14.1 billion people.

The models predict that the number of people will be smaller in a richer world, as a larger number of developed nations result in lower birth rates. If that's the case, the high population scenarios provide the biggest risk: Not only will more people be living along shorelines, but the world will be less able to protect them financially.

To that end, the authors assume in their analysis that every country has protective dikes in place by 2100. A richer world would be able to build higher walls over time to match the climbing oceans, while poorer nations could not. The authors call this "enhanced protection" versus "constant protection."

And the difference in suffering is sizable -- by hundreds of billions of dollars annually.

"What I like about this paper is it shows the cost," said Benjamin Horton, an expert on sea-level rise at Rutgers University who did not contribute to the paper. "We keep missing opportunities to redevelop our coastlines to make them more sustainable. Hurricane Sandy is a classic example. That devastated the Jersey shoreline, but the Jersey shoreline was just rebuilt exactly how it was."

The paper's ambitious nature creates some uncertainties. It's difficult to project the rate of sea-level rise 90 years in the future, though its assumptions are in line with the United Nations' Intergovernmental Panel on Climate Change.

The paper also incorporates other futuristic elements, like the rate of population growth and the size of the world's economy. Lastly, it assumes that dikes will be the dominant method of adapting to sea-level rise, when options like dunes, wetlands and retreat are some other possibilities.

"Sea-level rise is basically one of the most certain impacts of climate change," Hinkel said. "We just know it's going to go up. We don't know by how much or by when. But it's going to rise. So our future planning must consider that."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500