Re­cent cli­mate pro­jec­tions have put some new cities in the crosshairs

Newsweek - - Climate Change - by FRED GUTERL

the th­waites glacier is about the size of a u.s. swing state and holds enough ice to raise sea lev­els by about 10 feet. This alone is scary enough to jus­tify its nick­name, the Dooms­day Glacier, but there’s more. The Th­waites sits along a 75-mile stretch of shore­line in Antarc­tica that serves to par­tially shield the vast West Antarc­tic Ice Sheet from the warm ocean wa­ters. The WAIS has enough ice to raise the seas by 200 feet.

Forty years ago, the Th­waites was thought to be shed­ding 40 bil­lion tons of wa­ter each year. Sci­en­tists re­cently upped that fig­ure to 250 bil­lion tons. To their alarm, a river of warm wa­ter ap­pears to be flow­ing be­neath the glacier, which can only has­ten the day when it col­lapses into the sea—it could be a cen­tury from now, or a few decades. No one re­ally knows.

We haven’t even talked about Green­land yet. An­other un­der­ground river of warm wa­ter was re­cently dis­cov­ered un­der the Nioghalvf­jerds­fjor­den Glacier, which is ex­pected to add be­tween a foot-and-a-half and 5 feet to ocean lev­els in the next 200 years.

These pro­jec­tions carry some un­cer­tainty, but one thing seems pretty clear: the next cen­tury will be tough for coastal city dwellers. Sea lev­els are ris­ing about 3 mil­lime­ters each year. By the end of the cen­tury, the oceans could rise at least 2 feet over 2005 lev­els, ac­cord­ing to a 2018 study in the Pro­ceed­ings of the Na­tional Academies of Sci­ence. Michael Mann, a cli­mate sci­en­tist, told NBC News that un­less emis­sions of green­house gases are abated, by the end of the cen­tury more than 650 mil­lion people will be liv­ing on land that is un­der wa­ter all or much of the time.

Cities will take the brunt of the im­pact. The last big sur­vey by the World Bank of cities around the world that are vul­ner­a­ble to cli­mate change was pub­lished in 2013, based on satel­lite data cap­tured in 2005. It found that hun­dreds of coastal cities around the world will be at height­ened risk of flood­ing in the next few decades. In the years since the study was pub­lished, risk cal­cu­la­tions have changed for the worse, says Stephane Hal­le­gatte, lead econ­o­mist at the World Bank’s global fa­cil­ity for dis­as­ter re­duc­tion and re­cov­ery and an au­thor of the report.

One change is that cities in Africa have grown quicker than ex­pected. That means that any list of vul­ner­a­ble cities would now have to in­clude new names, like Lagos in Nige­ria and Dar es Salaam in Tan­za­nia. A dan­ger­ous com­bi­na­tion of ris­ing seas and poverty make these cities in­creas­ingly vul­ner­a­ble. Many of the cities on the orig­i­nal 2013 list have im­proved their prospects greatly by tak­ing steps to pro­tect them­selves against flood­ing. These in­clude Guangzhou and Shang­hai in China, Manila in the Philip­pines, Can Tho in Viet­nam and New Or­leans in the U.S.

Some cities in the de­vel­oped world haven’t ad­e­quately ad­dressed the ris­ing threat. In par­tic­u­lar, Mi­ami and New York are vul­ner­a­ble to storm surges that be­devil the east coast of the U.S., and nei­ther has im­ple­mented ad­e­quate pro­tec­tions. They would do well to take a page from Lon­don, Am­s­ter­dam and Rot­ter­dam, which have in­vested in dykes, bar­ri­ers and drainage sys­tems.

The wors­en­ing outlook on sea-level rise is prompt­ing a change in how people think about flood­ing and plan for it. “People re­al­ize that it’s just not pos­si­ble to pre­vent all floods, so you have to learn to live with the wa­ter and ac­cept that it will some­times have an im­pact,” says Hal­le­gatte. “We can­not live be­hind taller and taller walls, be­cause at one point, the con­se­quences of one of those walls fail­ing be­comes too big.”

The Nether­lands is at the fore­front of new liv­ing-with-wa­ter tech­niques. They are build­ing spa­ces in their cities for flood wa­ter to col­lect—ar­eas of low den­sity that are rel­a­tively easy to evac­u­ate—to pro­tect ar­eas of high pop­u­la­tion den­sity. They are us­ing the dy­nam­ics of the river deltas to dis­trib­ute sand in such a way that main­tains pro­tec­tive dunes. Such quasi-nat­u­ral sys­tems are both less ex­pen­sive to build and fail more grace­fully than a big wall. “It’s what we call na­ture-based so­lu­tions,” he says. “In­stead of try­ing to use con­crete to just pro­tect ev­ery­thing, you try to use nat­u­ral mech­a­nisms.”

“We see people from all con­ti­nents, all in­come lev­els, ask­ing the same ques­tion: how to man­age in­creased flood­ing over the next 10 or 20 years,” says Hal­le­gatte. Here are five cities that have grown rel­a­tively more vul­ner­a­ble in the last few years.

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