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Rising sea levels may threaten millions along U.S. coasts, studies find

Higher tides don’t just threaten the Maldives and Mumbai — Maryland’s at risk, too.

Areas shaded gray in this interactive map represent coastal lands around New Orleans that today lie less than three feet above sea level and, according to new research, face a 1 in 6 chance of being flooded by higher sea levels and/or stronger storm surges sometime in the next eight years.

When Americans think about rising sea levels and their likely impact, we tend to focus on low-lying and lightly populated places like the Maldive Islands, Tuvalu, Kiribati … atoll states for whom submergence is more or less a certainty.

Occasionally we might remember that the Netherlands is also at risk. Or New Orleans.

Two reports in last week’s news turn that kind of thinking on its head.

One pointed out the threat to major cities, and huge populations, throughout Southeast and Central Asia. Another offered a sobering — and, to my eyes, a rather new and rare — assessment of vulnerabilities throughout the coastal regions of our own United States.

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Perhaps you saw the brief AP story in the Strib, reporting on a new study from the Asian Development Bank. This analysis suggests that rising sea levels, driven by global warming, could threaten as much as one-third of Southeast Asia’s population with evacuation in the face of flooding and other disasters during the rest of this century.

Refugees without refuge

A better piece in The Economist looked at the striking figure of 42 million Asians displaced by weather in 2010 and 2011 and noted they have to relocate somewhere — most likely, big cities. However, those cities can’t really offer much refuge because, they, too  

are often in the coastal areas most at risk from rising sea levels. In East Asia such cities include Guangzhou, Seoul and Nagoya. In South Asia Bangladesh’s capital, Dhaka, is vulnerable, as are Kolkata and Chennai. Substantial parts of Mumbai, a city of around 20 million people, are already below sea level. …

Last year heavy rainfall overwhelmed the Chao Phraya river system, on which Bangkok sits, and the Thai capital only just avoided a catastrophe. As it was, hundreds died, and the World Bank estimates the floods cost Thailand $46 billion in economic damage.

Given its readership, perhaps, The Economist found it unnecessary to point out that the aftershocks of such catastrophes ripple through the entire global economy, especially when it’s already shaky. These are regional catastrophes with worldwide consequences.

As for our own coastal regions, a grim picture can be drawn from two new studies that made the front page of The New York Times but, best as I can tell, escaped mention in local media until yesterday, when a brief reference turned up some 20 screens into Paul Douglas’ Strib blog. Here’s the top of the Times story:

About 3.7 million Americans live within a few feet of high tide and risk being hit by more frequent coastal flooding in coming decades because of the sea level rise caused by global warming, according to new research.

If the pace of the rise accelerates as much as expected, researchers found, coastal flooding at levels that were once exceedingly rare could become an every-few-years occurrence by the middle of this century.

By far the most vulnerable state is Florida, the new analysis found, with roughly half of the nation’s at-risk population living near the coast on the porous, low-lying limestone shelf that constitutes much of that state. But Louisiana, California, New York and New Jersey are also particularly vulnerable, researchers found, and virtually the entire American coastline is at some degree of risk.

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Higher tides and storm surges

The research cited here is two separate but related analyses. One study simply calculated the amount of coastal land that would be underwater if sea levels rose as much as one meter, a middle-range estimate these days for what’s likely over the next 90 years.

As climate-impact modeling goes, this is comparatively straightforward and noncontroversial stuff. If you know how much of, say, Florida’s Atlantic coast is three feet or less above today’s average high tide line, you know how much will be new seabottom if the ocean rises three feet.

The second analysis added in the effect of storm surges, drawing on decades of data collected by more than 50 monitoring stations along America’s Atlantic, Pacific and Gulf coasts, and additionally factored in the probability that storm surges will intensify as things get warmer.

Both studies were undertaken for Climate Central, a New Jersey outfit that conducts and publishes original research and other material on “the clear and present danger” of global warming.

Some may seize on that frank acknowledgement as justification to dismiss the findings. I find it admirably transparent — but, I’ll admit, it moved me to look a little harder for warning signs in the reports and in their authors’ credentials. I found none.

Of course you can decide for yourself, after reviewing the papers and author affiliations as published in Environmental Research Letters. Or you might be interested in the assessments reported by a few of the country’s leading journalists on environmental subjects:

Seth Borenstein, Associated Press: (E)xperts at the U.S. Geological Survey and the National Oceanic Atmospheric Administration who weren’t part of the studies said the results make sense and were done by experts in the field.

“All low elevation places in the many urban areas along the coast will become more vulnerable,” said S.  Jeffress Williams, scientist emeritus for the USGS, who wasn’t part of the studies. He pointed to Boston, New York City, Norfolk, Va., New Orleans, Charleston, S.C., Miami and Washington and its Virginia suburbs. “More people and infrastructure will be at increasing risk of flooding.”

Curtis Morgan, Miami Herald: The report from Climate Central, an independent research and journalism organization, suggests Miami-Dade and Broward counties alone have more people vulnerable to flooding than any state except Florida and Louisiana.  … (It) echoes and expands on previous studies by universities and government agencies that have pinpointed South Florida as ground zero for global warming impacts … .

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Not just Mumbai but Maryland

Tim Wheeler, Baltimore Sun: Scientists with Climate Central, an independent nonprofit journalism and research organization, have produced maps showing how even small increases in sea level rise are likely to push storm surges onto shore. They’ve also published their findings in peer-reviewed journals.

In Maryland, past and future global warming nearly doubles the estimated odds of “century” or worse floods occurring within the next 18 years, they say meaning floods so high they would historically be expected just once per century.  Elsewhere along the nation’s coastline, the risks triple.

Here’s Climate Central’s own nontechnical summary of the research:

Global warming has raised global sea level about 8 inches since 1880, and the rate of rise is accelerating. Rising seas dramatically increase the odds of damaging floods from storm surges.

A Climate Central analysis finds the odds of “century” or worse floods occurring by 2030 are on track to double or more, over widespread areas of the U.S. These increases threaten an enormous amount of damage. Across the country, nearly 5 million people live in 2.6 million homes at less than 4 feet above high tide a level lower than the century flood line for most locations analyzed.

And compounding this risk, scientists expect roughly 2 to 7 more feet of sea level rise this century a lot depending upon how much more heat-trapping pollution humanity puts into the sky.

That last phrase is sure to set off the global-warming deniers, who undoubtedly will claim that if the scientists can’t agree on exactly how much sea levels will rise, then none of their predictions have any credibility.

Of course, this ignores the reality that much of the variability in sea-level predictions is rooted in such sheer unknowables as how fast the ice sheets over Greenland and western Antarctica will melt.

Interactive map of impacts

Other readers will find it sobering to consider the impacts of even small rises in sea level. And some may find it interesting to consider the project’s interactive map, which allows users to pick a piece of coastline and manipulate a slider to visualize inundation zones at various levels of sea-level rise.

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It’s an alarming picture, or series of pictures, especially when considered alongside this helpful context from the Christian Science Monitor, which noted that current development patterns in America’s coastal lands will only make matters worse:

In 2009, researchers with the US Environmental Protection Agency, the Woods Hole Oceanographic Institution, and several regional planning agencies reviewed development plans for communities up and down the East Coast. Nearly 60 percent of coastal lands lower than 1 meter above sea level have been slated for some form of development. Less than 1 percent of the land has been earmarked for conservation.