New Orleans faces a terrifying future as sea levels rise

New Orleans after KatrinaMario TamaA woman jogs along a levee along the Mississippi River with the city skyline in the distance on May 16, 2015 in New Orleans, Louisiana.

It’s been 10 years since Hurricane Katrina devastated New Orleans and other parts of the Gulf Coast. But the Crescent City, a cultural treasure that’s home to almost 400,000 people, faces even greater risks in the future.

Most of the city is already below sea level, protected by an unreliable system of levees.

Flood risk will grow more severe as rising sea levels and sinking coastal land produce a local increase of at least four feet by the end of the century. And then there’s the inevitable increase in major storm surges caused by extreme weather events.

We’ve created a guide to the crises ahead and the city’s best hope for survival.

More than 50% of New Orleans is already below sea level. The only things keeping the city safe are levees and flood walls.

Note: The Mississippi appears so high because the banks on either side rise higher than anywhere else in the city, and the technology used to measure sea level doesn't function properly on water itself.

But sea levels are projected to rise by around 4.5 feet this century as global warming causes water to expand and land ice to melt.

Sea levels are rising faster in Louisiana than almost anywhere else due to rapid sinking of marshy coastal land (orange shows land that disappeared between 1937 and 2000).

Here's a look at New Orleans elevations by the end of the century.

With Katrina, we already saw the flooding and destruction that could happen again and again as the situation gets worse. The hurricane hit the city in late August of 2005.

The storm surge was more than the levees that stop water from flooding the city every day could handle and more than 80% of the city flooded. The storm killed more than 1,800 people in total, did $75 billion worth of damage to New Orleans, and left more than 100,000 homeless.

Some describe the hundreds of thousands who never returned to New Orleans as the first major wave of climate refugees.

Source: Grist

This isn't just a future risk. 'The timeframe is -- it's already happened,' says Alex Kolker, an adjunct professor in the Department of Earth and Environmental Sciences at Tulane who focuses on changing coastal systems, especially the Louisiana coast. But the risk is only getting worse.

It doesn't help that the land is sinking. The Louisiana coast has lost almost 2,000 square miles of land since the Mississippi's natural flow, which deposited sediment that replaced land carried away, was diverted in 1932 to protect communities from the river's seasonal floods. All the land in red is gone already, and the yellow patches are expected to disappear in the next 35 years.

Source: NOAA

Local gas and oil production has been shown to accelerate the dangerous process of subsidence.

An aerial view is seen of the town of Port Fourchon and its surrounding marshes in Louisiana, May 11, 2010. U.S. Army National Guard troops dropped sandbags from helicopters to fill in breaks in beaches to protect the marshes from the BP oil spill offshore.

Source: USGS

Much of what has been lost is valuable marshland, which helps buffer storm impacts and absorb flooding. The marsh photographed here, part of Barataria Preserve, is likely to be gone in a few years.

Source: Matter

In some areas of coastal Louisiana, water is already rising between one and three to four centimeters a year -- the same rates predicted for the rest of the world by end of the 21st century.

Source: Kolker

A forensic engineer who analysed why the levees failed to protect New Orleans and the surrounding area during Katrina said that building these protective structures on this type of terrain is 'like putting bricks on Jell-O.'

Source: The Lens

And then there's the steady increase in hurricane strength and frequency as water temperature increases.

Global annual power and frequency of tropical cyclones averaged in 10-y blocks for the period 1950 -- 2100, using historical simulations for the period 1950 -- 2005 and the modelled for the period 2006 -- 2100. For more info, see source link to paper.

Source: Proceedings of the National Academy of Sciences

America's Hurricane Alley is going to get a lot worse in the coming years.

Hurricanes and sea level rise aren't the only threats to New Orleans. Temperatures are on the rise too.

Ice is being distributed here in the wake of Hurricane Isaac.

Louisiana's average temperature is going up, according to NOAA, and the number of days over 65 degrees is expected to increase 43% by mid-century, according to a National Climate Assessment report released last year.

Heat kills more people each year than cold, hurricanes, tornadoes, floods, or any other weather-related cause.

Source: CDC

And in an already sweltering city like New Orleans, with more than 70 days a year that top 90 degrees, further increases in temperature pose serious health risks -- especially for elderly residents and families who can't afford air conditioning.

Source: NOAA

Increased temperatures could also have a serious effect on the city (and Gulf region's) famed seafood industry. Heat makes algal blooms that kill sea life more common, and it's also stressing Caribbean reefs, which are the source for much sea life in the Gulf.

Source: NRDC

The OECD has estimated that climate change could put more than one million people and $200 billion at risk from damage to New Orleans and the surrounding area by the 2070s. It's one of the most vulnerable cities in the world, according to a recent study in Nature Climate Change.

There is a plan in place to try to protect the region by restoring valuable marshland and figuring out how to let the Mississippi's floods flow more naturally, along with building up levees and other protective structures -- but it's approximately a 50-year, $50 billion plan, and one where the funding for the entire thing is not there.

Source: Kolker, PRI

The plan itself has a variety of ways to both restore protective natural habitats and to bolster protection for human settlements.

New levees would be built up around New Orleans and swamps, marshes, and barrier islands could be restored with sediment from a more free Mississippi.

If the ambitious plan to protect Louisiana doesn't get funded, then by the end of the century, warns professor McCarthy at Harvard, 'New Orleans is gone.'

Lessie Lewis stands on the front porch with her granddaugher Kodi Lewis, 6, as flood waters surround their home on St. Roch ave. as Hurricane Isaac makes land fall in New Orleans, Louisiana August 29, 2012.

Source: National Climate Assessment, Scientific American

You've seen how climate change could put New Orleans underwater.

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