New Orleans is sinking just as the waters are rising

When it comes to climate, the latest news for my lifelong hometown of New Orleans is not very good at all. As many people know — and as Hurricane Katrina and the flooding that followed made quite clear in 2005 — much of the Crescent City sits below sea level, which is why the city’s levees and its other defense mechanisms such as flood pumping stations are so critical. When several key levees failed after Katrina struck, the lower-lying neighborhoods were essentially sitting ducks.

It’s a complicated problem. On one hand, the city’s location near the mouth of the mighty Mississippi as well as the Gulf of Mexico and Louisiana’s bayou country exposes New Orleans to both conventional floodwaters and powerful storm surges from tropical storms. But flood-mitigation measures — including the levee system and the pumping stations — can cause parts of New Orleans to sink even lower below sea level; so can human activities such as factories that suck up groundwater, or other kinds of over-development.

Government officials — tasked with allocating millions of dollars on flood control measures for a large American coastal city — have been working to use state-of-the-art technology to map exactly where the land is subsiding the fastest, thus posing the greatest risk. In the most recent program, NASA Jet Propulsion Laboratory in Pasadena, Calif., worked with scientists at UCLA and Louisiana State University to develop a scheme to fly an aircraft on a fixed route every July from 2009 through 2012 and use radar to find where land was sinking and by how much.

In some New Orleans locations, the earth was subsiding by about two inches a year, which is stunningly fast in geological terms. Here’s more on what the findings newly reported this week mean for my hometown:

Up to two inches a year were the highest subsidence rates found, observed mostly near the Mississippi River by industrial areas such as Norco and Michoud. Other high subsidence rates were found in the city’s Upper and Lower Ninth Ward, Metairie, and Bonnet Carré Spillway, where the water levels hiked up another 1.6 inches a year.

The subsidence is primarily caused by groundwater pumping and surface water pumping (known as dewatering). Other factors include faulting; deposited sediments weighing down the Earth’s crust; human withdrawal of water, oil, and gas; shallow sediments compacting; and perpetual land movement from glaciers during the last glacial period.  

Louisiana has been among the US locations hardest hit by climate change. The government recently set aside a $48-million grant to move the entire community of the sinking Isle de Jean Charles to drier land. Washington, D.C. is also sinking and could drop at least six inches in the next hundred years, according to researchers. Moreover, 10,000 refugees from the Marshall Islands, which have sunk to more than six feet above sea level, have sought refuge in Arkansas, escaping the dire consequences of climate change at home.

Overall, global sea levels have risen about three inches since 1992 because of global warming. Scientists predict that they can rise another three feet in the next century or two. In some areas, sea levels have risen up to nine inches. The rising sea levels are caused primarily by the expansiveness of warm water, which takes up more space than cooler water, and the melting of the ice caps, during which more water runs into the ocean.

That’s the problem. With the area’s propensity for tropical storms, the sinking of New Orleans would be a big problem in the best of times. But these are not the best of times. To the contrary, scientists tell us that April once against set a monthly record for average high temperatures — the 12th consecutive record-shattering month. That is unprecedented. And it’s hardly the only bad news on the climate front; this week it’s been reported that the unnaturally warm waters are threatening the existence of the Great Barrier Reef off Australia.

Millions of Americans understand the urgency of the global climate crisis and the need for immediate action such as reducing our use of fossil fuels — but many still don’t. For those who live in and around New Orleans, the latest news from NASA should be a wake-up call. The threat from global warming is already upon us.

Read more about sinking land levels in New Orleans from the Christian Science Monitor: http://www.csmonitor.com/Science/2016/0518/How-fast-is-New-Orleans-sinking-Faster-and-faster-says-new-study

Here’s the latest on April’s global temperature record: http://www.philly.com/philly/blogs/weather/Warming-trend–Another-month-another-record.html