都市缘何成为热岛?

Take a closer look at how much worse it can be for people living in cities. 80 million Americans live in the cities with populations of more than 100,000 and it's common for the downtown areas of those cities to be 5 degrees hotter than surrounding suburbs. Tonight ABC's Ned Potter takes us to some of the hottest places in the country.

This is how downtown Atlanta looks in the computer animation¹ from NASA. And this is how it looks when you add temperature data. The warmest areas, the buildings and roads, are in red. Scientists talk of modern cities as heat islands where there're miles of asphalt and concrete. On a day like today, the cities are 2 to 10 degrees hotter than the countryside around them.

In a major US city, you know, a quarter to a half of the land is covered by black surfaces. In the hot sun, they just get hotter, and hotter, and hotter, as the wind blows over them, they just heat up the whole city.

Not only do cities bake in the sun, they don't cool off the way countryside does. If New York, for instance, has a high tomorrow of 97, it'll only drop to 83 overnight.

That's all that brick and cement road pavement which is retaining the heat and very slow to release it. So it's very very tough to stay cool inside the city metropolitan² area itself.

The National Weather Service says heat causes more death than almost any other kind of weather, more than anything except the most catastrophic hurricanes such as Katrina last year.

Cities that are hotter because of the heat island have more air pollution, more smog, and that affects people with asthma³ and cardiovascular disease.

But some of the solutions are simple, such as planting more trees or using less black asphalt. A building with a white roof, we are told, can save 20 to 50 percent on the air conditioning.

Ned Potter, ABC News, New York.

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computer animation :计算机直观显示
NASA:the National Aeronautics and Space Administration 美国国家航空和宇宙航行局
asphalt:a black sticky substance that is used for making roads 沥青
cardiovascular:medical connected with the heart and the blood vessels 心脏血管的

1 animation   

n.活泼，兴奋，卡通片／动画片的制作

参考例句：

• They are full of animation as they talked about their childhood.当他们谈及童年的往事时都非常兴奋。
• The animation of China made a great progress.中国的卡通片制作取得很大发展。

2 metropolitan   

adj.大城市的，大都会的

参考例句：

• Metropolitan buildings become taller than ever.大城市的建筑变得比以前更高。
• Metropolitan residents are used to fast rhythm.大都市的居民习惯于快节奏。

3 asthma   

n.气喘病，哮喘病

参考例句：

• I think he's having an asthma attack.我想他现在是哮喘病发作了。
• Its presence in allergic asthma is well known.它在过敏性气喘中的存在是大家很熟悉的。