Environment@Harvard

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Volume 3, Issue 2

Environment @Harvard H a r v a rd U n i ve r s i t y C e n t e r f o r t h e E nv i r o n m e n t www.environment.harvard.edu

Rising Seas, Imperiled Cities

Coastal regions must prepare, and Boston is a case study

GRAPHIC COURTESY MICHAEL WILSON

By Corydon Ireland

A

round the world, oceans are warming and expanding. Vast ice sheets are crumbling and melting into the sea. The result is global sea-level rise, which will be one of the most dramatic and destructive consequences of climate change. Of particular concern to human civilization is the fate of the world’s coastal cities. Conservative estimates of sea level rise by the Intergovernmental Panel on Climate Change (IPCC) project increases of more than half a foot to two feet by the year 2100. More up-to-date analyses by the Arctic Monitoring and Assessment Program, which account for the effects of melting ice sheets around the globe, suggest that sea level will rise three feet to as much as five feet or more by 2100

(see "The Science of Rising Seas," page 4). Ninety years from now, in other words, vast, densely populated coastal areas around the world will be under water, including major cities—unless they prepare. CITIES AT RISK Getting ready for sea-level rise is every city’s problem. Without action, in fact, rising seas will sooner or later alter most of civilization’s urban footprint. Coastal floodplains worldwide are crowded with cities often built no more than 3 feet above sea level. More than 2 billion people—an estimated 37 percent of the world’s population—live within 60 miles of the coast and would be affected, directly or indirectly, by incursions of the sea.

A storm surge model of Boston depicts land use impact of a typical high tide (left) and a worstcase scenario storm surge of 5.5 meters (right). Each dot accounts for 100,000 square feet of either residential (yellow), commercial (red), or industrial (purple) built structure.

In sheer economic terms, the stakes of sea-level rise in urban areas are particularly high. An added 0.5 meters (20 inches) of ocean water by the year 2050 would put $28 trillion in assets at risk in the world’s 136 port megacities, according to a 2009 report of scientists and insurance experts assembled by World Wide Fund/Allianz, a global investment and insurance company. On the northeastern coast of the United States, the expected maximum rise in sea

Harvard University Center for the Environment 1


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