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The Atmosphere
From Grolier's New Book of Popular Science
http://scienceworld.scholastic.com/Earth-ScienceNews/2012/09/the-atmosphere
THE OZONE HOLE
The stratosphere contains within it a layer of ozone that acts as a "sunscreen," shielding life on Earth's surface from the
Sun's harmful ultraviolet radiation. Today human activities are severely depleting this ozone shield. The extent of this
depletion—and what can be done about it—are now the subjects of much study. (Ozone depletion should not be
confused with ozone pollution, which occurs at ground level. Ironically, car exhaust and other human activities produce
an overabundance of ozone in the lower atmosphere, where it damages both plants and human health.)
In the late 1970s, scientists first noticed the appearance of an ozone hole over Antarctica. They determined that some
thinning of the ozone layer was natural during the Antarctic spring. But this thinning had been greatly increased by the
presence of human-made chemicals in the upper atmosphere.
The main culprit was, and still is, the chlorine molecules found in industrial chemicals known as halogenated
hydrocarbons. The best known are the chlorofluorocarbons, or CFCs, used in aerosol sprays, refrigeration, and airconditioning systems. In the stratosphere, ultraviolet light breaks down CFCs so that they release their destructive
chlorine.
The chlorine molecules then react with ozone molecules. Each chlorine molecule can destroy as many as 100,000 ozone
molecules. It does so by speeding a reaction in which ozone (O3) is converted into ordinary oxygen (O2). Chlorine does
the most damage in areas of the atmosphere where clouds of ice or volcanic dust further speed its reaction with ozone.
In 1987, many nations of the world agreed to reduce the emissions of CFCs by 50 percent by 1998. Then, after the
danger of ozone depletion became even more apparent, the nations agreed to an outright ban on CFCs by 2000. But
scientists warn this is not enough. Experts are urging a complete ban of chlorine-emitting chemicals by 2030. Bromine
and nitric oxide also deplete stratospheric ozone.
Meanwhile, depletion of the ozone layer continues to worsen, causing an increase in the amount of ultraviolet radiation
that reaches Earth. NASA's Total Ozone Mapping Spectrometers (TOMS) aboard several satellites have reported that the
fluctuating ozone hole over Antarctica measures some 10 million square miles (25.9 million square kilometers)—larger
than the area of North America. Thinning has been recorded over every continent. The elevated levels of ultraviolet
radiation may already be harming wildlife and contributing to the increased occurrence of skin cancer.
Atmospheric scientists continue to monitor ozone levels with TOMS and other sophisticated instruments aboard aircraft
and balloons and on the ground, as part of Mission to Planet Earth—NASA's long-term effort to study Earth as a global
environmental system. Researchers also investigate the complex ways in which ozone-destroying chemicals reach the
stratosphere and alter the ozone there. And there are new concerns. One is the increasing number of rocket launches in
the world's growing space programs. Every type of rocket engine causes some ozone loss. Experts warn that rocket
launches must be restricted to prevent continued ozone destruction. Another concern is climate change. Ozone
depletion worsens when the stratosphere becomes colder. But because global warming traps heat in the troposphere,
less heat reaches the stratosphere, which makes it colder. Global warming and unregulated rocket launches could
accelerate ozone destruction far beyond the damage caused by CFCs.
THE GREENHOUSE EFFECT
Research has shown that human activities can change the climate in other ways as well. The burning of oil, coal, and
natural gas has produced a steady increase in the amount of carbon dioxide in the atmosphere. Like water vapor, carbon
dioxide and certain other gases absorb and hold heat in a sort of blanket around the world. This phenomenon has been
termed the greenhouse effect because the gases act like the heat-trapping glass of a greenhouse.
While natural greenhouse gases are vital to prevent our world from freezing over, a marked increase may spell big
trouble. Indeed, there is disturbing evidence of climate change: melting glaciers; forest fires; drought; heat waves; moresevere storms; and the loss of certain plant and animal species.
Melting polar ice can result in rising sea levels, which could impact coastal communities. Climatologists say that fossilfuel use has led to the fastest warming trend in Earth's history. In fact, the three warmest years on record have all
occurred since 1998. Studies suggest that Earth's average temperature could increase 2° to 10° F (1° to 6° C) by 2100 if
steps are not taken to reduce greenhouse-gas emissions.
Directions: After reading the entire article, answer the questions below. Highlight or underline where you got the
answers within the article itself.
1. Explain. What are the main causes of the depletion of the ozone layer?
2. According to the article, what products contain CFC’s?
3. What are some of the negative side effects of the thinning or holes in the ozone layer?
4. What is the evidence that supports the reality of climate change?
5.
What is the impact of climate change?