托福阅读是托福考试中最容易拿高分的一项，但很多同学因为没有找到好的复习方法及材料而与高分失之交臂，今天启德考培小编为大家带来托福阅读复习材料之美国科学文摘精选，希望能帮助到正在托福备考的同学们。

　　The Planet Earth

　　The 2000 Antarctic Ozone Hole Was Largest Ever

　　The 2000 Antarctic Ozone Hole was the largest ever observed. Earth's wetter

　　upper atmosphere may delay global ozone recovery.

　　NASA researchers have found that an increase in water vapor in the

　　stratosphere, stemming partially from greenhouse gases, may delay ozone

　　recovery and increase the rate of climate change.

　　To check on the long-term stratospheric cooling and ozone depletion, NASA put

　　data from satellites and other remote sensors into its GISS global climate

　　model. It was the first study to link greenhouse gases to increased ozone

　　depletion over populated areas.

　　Water and ozone. Climate models show cooler stratospheric temperatures happen

　　when there is more water vapor present. Water vapor also leads to the

　　breakdown of ozone molecules.

　　The stratosphere is the dry layer of the atmosphere above the troposphere,

　　where temperatures increase with height.

　　According to satellite data, upper atmospheric temperatures around the world -

　　at altitudes of 20 to 35 miles high -- have cooled between 5.4 and 10.8

　　degrees Fahrenheit over recent decades.

　　Driving forces. NASA found two driving forces behind the change in

　　stratospheric moisture:

　　Increased emissions of the greenhouse gas methane are transformed into water

　　in the stratosphere, accounting for about a third of the observed increase

　　in moisture there.

　　More water is transported from the lower atmosphere. Warmer air holds more

　　water vapor than colder air, so the amount of water vapor in the lower

　　atmosphere increases as it is warmed by the greenhouse effect. Greenhouse

　　gases, such as carbon dioxide and methane, may enhance the transport of

　　water into the stratosphere.

　　The increased transport of water vapor to the stratosphere seems likely to

　　have been induced by human activities.

　　Ozone destruction. Rising greenhouse gas emissions account for all or part of

　　the water vapor increase, which causes stratospheric ozone destruction.

　　When more water vapor works its way into the stratosphere, the water molecules

　　can be broken down, releasing reactive molecules that can destroy ozone. If

　　the trend of increasing stratospheric water vapor continues, it could increase

　　future global warming and impede ozone stratospheric recovery.

　　The impact on global warming comes about because both water vapor and ozone

　　are greenhouse gases, which trap heat leaving the Earth. When they change, the

　　Earth's energy balance changes too, altering the surface climate.

　　Warmer ground. Increased water vapor in the stratosphere makes it warmer on

　　the ground by trapping heat, while the ozone loss makes it colder on the

　　ground.

　　Water vapor has a much larger effect, so that overall the changes increase

　　global warming.

　　Although ozone depletion cools the Earth's surface, repairing stratospheric

　　ozone is important to block harmful ultraviolet radiation. Other greenhouse

　　gas emissions also need to be reduced.

　　UARS satellite. NASA combined seven years of data from the Upper Atmosphere

　　Research Satellite (UARS) Halogen Occultation Experiment (HALOE) with data

　　collected on the ground to paint a complete picture of the upper atmosphere.

　　NASA's HALOE was aboard the UARS spacecraft when it was launched September 12,

　　1991 as part of the Earth Science Enterprise Program. The spacecraft's mission

　　at launch was to improve understanding of stratospheric ozone depletion by

　　analyzing vertical profiles of ozone, hydrogen chloride, hydrogen fluoride,

　　methane, water vapor, nitric oxide, nitrogen dioxide, and aerosols.

　　Fourteen years of lower stratospheric measurements have revealed large

　　increases in water vapor. Though some older studies conflict with lower

　　stratospheric observations of water vapor trends, new studies agree with the

　　increases, showing they have been taking place for more than four decades.

　　What Is An Ozone Hole?

　　Ozone molecules are made up of three atoms of oxygen. They comprise a thin

　　layer of the atmosphere that absorbs harmful ultraviolet radiation from the

　　Sun.

　　Most atmospheric ozone is found between approximately six miles and 18 miles

　　above the Earth's surface.

　　An ozone "hole" is what scientists call an "ozone depletion area" of in that

　　region of Earth's atmosphere.

　　Really big hole. The largest-ever ozone hole was detected on September 6,

　　2000, by the Total Ozone Mapping Spectrometer (TOMS) aboard a NASA satellite

　　known as Earth Probe (TOMS-EP).

　　The Antarctic ozone hole is three times larger than the entire land mass of

　　the United States, making it the largest such area ever observed.

　　The hole had expanded to a record size of 11 million square miles. The

　　previous record was 10.5 million square miles in September 1998.

　　Scientists were surprised by its enormous size. The lowest readings in the

　　Antarctic ozone hole usually are observed in late September or early October

　　each year.

　　Frail layer. The year 2000 observations reinforced concerns about the frailty

　　of Earth's ozone layer. Although production of ozone-destroying gases had been

　　curtailed under international agreements, concentrations of the gases in the

　　stratosphere have been reaching their peak.

　　Due to their long persistence in the atmosphere, it will be many decades

　　before the ozone hole is no longer an annual occurrence.

　　Antarctic vortex. The year 2000 saw an extremely intense Antarctic vortex --

　　an upper-altitude stratospheric air current that sweeps around the Antarctic

　　continent, confining the Antarctic ozone hole.

　　Variations in the size of the ozone hole and of ozone depletion accompanying

　　it from one year to the next are not unexpected.

　　NASA instruments have been measuring Antarctic ozone levels since the early

　　1970s. Since the discovery of the ozone hole in 1985, TOMS has been a key tool

　　for monitoring ozone levels above Earth.

　　TOMS-EP and other ozone-measurement programs are important parts of a global

　　environmental effort of NASA's Earth Science enterprise, a long-term research

　　program designed to study Earth's land, oceans, atmosphere, ice and life as a

　　total integrated system.

　　To learn more:

　　Goddard Institute for Space Studies

　　Upper Atmosphere Research Satellite

　　Halogen Occultation Experiment

　　Largest ozone hole detected by TOMS

　　TOMS ozone data and pictures

　　NASA Says Wet Upper Atmopsphere Delays Ozone Recovery

　　NASA Press Release: Wetter Atmopsphere May Delay Ozone Recovery

　　Inner Planets:MercuryVenusEarthMars

　　Outer Planets:JupiterSaturnUranusNeptunePluto

　　Other Bodies:MoonsAsteroidsComets The Voyagers

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