Vulnerable cities

Sea levels will keep rising as more glacial meltwater pours into the oceans. By the year 2100, they are likely to be 8-24 in (20-60 cm) higher than they are now, provided that nothing catastrophic happens to the great continental ice sheets of Greenland or Antarctica. This may not seem too threatening, but many of the world's great cities are built on low-lying coasts, and are at risk from flooding. One of the most vulnerable is Shanghai in China—a city of 18 million people built on land that is just 10-16 ft (3-5 m) above sea level. Currently its sea defenses are just adequate to prevent flooding by storms in the East China Sea, but they may not be able to cope as sea levels rise.

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STORM WARNING

Hurricanes are likely to become more powerful as ocean surface temperatures rise, and they will probably occur over a wider area of the tropics. Outside the tropics, increased evaporation of water from warmer oceans will also lead to more intense storms over nearby land, causing fast-moving flash floods of the type that devastated Boscastle, England in 2004. These cars were swept out to sea by a wall of water, mud, and rubble that surged down a river valley after an unusually heavy summer thunderstorm.

SHIFTING VEGETATION ZONES

As the polar regions warm up and the subtropics turn to deserts, wild plants will creep toward the poles. Evergreen trees like these pines will move into treeless Arctic tundra, and in warmer, drier areas, grass will take over from woodland. But large tracts of farmland may prevent this natural migration, and many species of wild plants could simply die out.

WILDLIFE EXTINCTIONS

If the average global temperature continues to rise as predicted by scientists, 15 to 37 percent of the world's wild animal and plant species could face extinction by 2050. These will include many specialized organisms, such as polar bears, reef corals, and rare flowers like this clamshell orchid from the Florida Everglades in the US. By contrast, more adaptable living things such as rats and cockroaches may flourish.

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