Unit 9   

    There's a famous saying that goes: "Everybody talks about the weather, but no one ever does anything about it!" Humans do, of course, affect the climate, as we know from scientists' warnings about everything from the greenhouse effect to nuclear winter. Conscious of our power to harm the environment, we can sometimes forget that as a species we are still helpless to control -- or even predict with any accuracy -- many of the powerful surprises that nature can spring on us. The first two texts in this unit examine the causes and effects of one of the world's most trouble-making natural environmental phenomena -- El Niño -- while Text C speculates about what factors are making our weather so wild, and what we might be able to do about it.

 Continue to practice and use your scanning skills. Before your reading Text C, scan Text C rapidly to answer the following question:

Text C

   1998 has been the hottest year on record. Under the summer skies, the driest and hottest since the 1930s Dust Bowl (干旱尘暴区), crops failed from New Jersey to California. In the water-starved Mississippi River, dredges (挖泥船) dug non-stop to keep open a channel for boats. A record-breaking heat wave closed Harvard University near Boston, while in Detroit, auto workers walked off the job when some workstation temperatures exceeded 100 degrees F. Later, in the fall, the century's fiercest hurricane swept through the Caribbean.

    Something strange is happening to our weather. And it didn't just begin this year. During the past two decades, the United States has seen three of the coldest winters and five of the warmest average years ever recorded. Elsewhere, weather has also been extreme: the former Soviet Union and India have experienced their highest temperatures ever, and snow has been falling on the usually sunny beaches of the French Riviera, South Africa and even subtropical Brazil.

    Why is our weather going wild? Are we headed for the next Ice Age? Or are we feeling the first fevers of the “greenhouse effect”, a global warming that could melt the polar icecaps and turn the world landscape (地貌) into a combination of tropical jungles and deserts? Scientists have several theories, no single one of which offers a satisfactory reason for our strange weather. Together, however, they begin to explain the climate puzzle.

   Greenhouse Gas. When we burn fossil fuels (principally coal and oil) we send extra quantities of carbon dioxide into the atmosphere. Since 1958, the proportion of CO2 in our air has risen 25 percent. Many scientists think that within a century this simple gas could devastate our world.

    How? Carbon dioxide in our atmosphere, like the glass in a greenhouse, lets sunlight pass through, then catches and retains some of the sunlight's energy as heat. This greenhouse effect warms the earth's climate. If CO₂ and other greenhouse gases vanished tomorrow, the earth would become overnight a frozen, lifeless world like Mars. But if these gases build up too much in the atmosphere, we get overheated. And in fact, all these gases have been increasing since the start of the Industrial Revolution.

    Atmospheric scientists say that CO₂ causes about half the greenhouse effect. Each year our skies receive five billion tons of CO₂ from the burning of fossil fuels, and up to half as much from the clearing and burning of almost 33 million acres of tropical forest. At the present rate of increase, the amount of this gas alone could double during the next century.

   One scientist calculates that the earth's average temperature already has risen during this century by one degree F., almost certainly because of the increase in greenhouse gases. Even without further atmospheric pollution, he estimates that trapped heat from gases we've already put in our skies will boost global temperatures another one to five degrees over 1980 levels in the next century.

   A warming of just a few degrees seems small until we realize that it approximates (接近) the rise in temperature that ended the last major Ice Age 100,000 years ago. If we don't slow the rate of warming, researchers fear that droughts and forest fires will become normal summer weather, while giant hurricanes will hit farther north and during more months of the year. And that's just the beginning. As the warming continues, according to this theory, polar icecaps will melt and ocean levels will rise by up to four feet during the next century, threatening such cities as New York, London, Beijing, and Seoul (汉城). Farmland will be devastated and water supplies contaminated (污染).

   Seeing Spots. Scientists used to assume that our sun shines with constant, steady brightness. But recent satellite measurements have confirmed that the sun turns its temperature up and down based on the 11-year cycle of magnetic “sunspots.” The more spots, the brighter the sun.

   The present cycle should peak around 2001, when our sun might burn even hotter than during the last sunspot peak, around 1990. But, oddly, recent studies indicate that this could bring colder winters as well as hotter summers for much of the Northern Hemisphere. Sunspots are thought to influence global wind patterns, and one effect is that a peak in sunspot activity tends to bring more cold air southward.

    In addition to this 11-year cycle, there are longer ones -- including an 80- to 100-year cycle that will heat to a peak around the year 2010, bringing an even brighter sun. But when sunspot numbers return to normal, the earth's climate could cool quickly -- quite possibly more quickly and much cooler than we'd like.

    Clearly, many different forces are now shaping and bending (使反常) the earth's climate. The past two decades have seen some wild weather, and the next one may well bring extremes unknown in living memory. But this need not bring disaster.

   Science and common sense offer ways to minimize the risk of devastating climate change. We can slow down the building of CO₂ in our atmosphere by increasing energy conservation; by protecting tropical forests; by designing automobiles that burn less gas per mile; by turning to renewable energy sources such as solar, hydro, wind, and possibly nuclear power. Fortunately, we have the tools for preventing disaster. It only remains for us to use them.

Text C