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VOA慢速英语[科技报道]好消息:地球臭氧空洞正在缩小

2016-09-12    来源:VOA    【      美国外教 在线口语培训

There is big news about the environment: Scientists say a hole in Earth’s protective ozone layer is starting to heal.

A new study confirms the hole is getting smaller. A report on the study was published late last month in the journal Science.

The scientists say the reason for the improvement is a reduction in the release of man-made chemicals into Earth’s atmosphere. These chemicals are called chlorofluorocarbons or CFCs for short.

“It’s a big surprise,” said Susan Solomon, the lead writer of the report. “I didn’t think it would be this early,” she said.

Solomon is an atmospheric chemist and works at the Massachusetts Institute of Technology.

Ozone is a form of oxygen gas. It is found in the air we breathe and in the upper atmosphere. Near Earth, ozone in the air is a danger to life. It is a pollutant. But the ozone layer, 10 to 50 kilometers up in the atmosphere, protects life on Earth. It helps to block dangerous ultraviolet (UV) waves from the sun. It stops them from reaching the planet’s surface.

Researchers first discovered the hole in the ozone layer over Antarctica more than 30 years ago.The new report credits the shrinking ozone hole to a worldwide ban on chlorofluorocarbons.

CFCs once were commonly used in many products, including aerosols, cleaning substances, refrigerators and plastics. Scientists found that when released into the air, the chemicals damaged the ozone layer, creating the hole.

CFCs were banned when world leaders signed an agreement called the Montreal Protocol in 1987.

Susan Solomon compared the ozone hole to a patient that needs healing.

“It isn't just that the patient is in remission,'' Solomon said. "He's actually starting to get better. The patient got very sick in the ‘80s when we were pumping all that chlorine into the atmosphere.”

Measurements taken in September showed the ozone hole has shrunk since the year 2000. The new numbers show that the hole is smaller by 4.5 million square kilometers. That is about half the area of the U.S. mainland.

One year was different, however. In 2015, the ozone hole got bigger, not smaller. After looking at scientific records, Solomon said that increase resulted from a natural event. She said it was caused by the eruption of the Calbuco volcano in Chile.

While the healing is coming earlier than many scientists expected, it is an ongoing, continuing process. The ozone hole will not be completely closed for at least another 30 years. Estimates are it will close by around 2050.

"We can now be confident that the things we've done have put the planet on a path to heal," Solomon said.

"There is a sense of ‘mission accomplished,''' said Mario Molina in an email to VOA. Molina works at the University of California, San Diego. He shared the 1995 Nobel Prize for Chemistry for his research on the ozone issue. He praised this latest study, but was not involved in it.

Not-so good news

However, there is other news about Antarctica that is not as good.

For the first time in four million years, Antarctica registered carbon dioxide (CO2) levels above the level of 400 parts per million. That information comes from U.S. scientists at the National Oceanic and Atmospheric Administration (NOAA).

“The far southern hemisphere was the last place on earth where CO2 had not yet reached this mark,” of 400 parts per million (ppm), said Pieter Tans. He is the lead scientist of NOAA's Global Greenhouse Gas Reference Network.

“Global CO2 levels will not return to values below 400 ppm in our lifetimes, and almost certainly for much longer,” he said.

Scientists say too much CO2 causes temperatures on Earth to rise.

CO2 levels usually go up in colder months. In the warmer months, plants in the northern hemisphere use some of it, and that lowers the levels. But NOAA notes that plants are not enough to stop the rise of CO2 levels. Those levels have risen every year since 1958, when measurements began.Tans said that evidence shows that the CO2 increase is caused “entirely by human activities.” These activities include burning oil and other fossil fuels for energy.

Because the burning of fossil fuel has been at a record high during the last several years, Tans said, the rate of CO2 increase has also been at a record high. He said some of the gas will stay in the atmosphere for thousands of years.

I’m Anne Ball.

And I’m Bryan Lynn.


_________________________________________________________________
Words in This Story

layer – n. amount of something spread over an area

ultraviolet – adj. rays of light that cannot be seen

chlorofluorocarbon – n. an organic compound that damaged the ozone layer

aerosol – n. a substance like hair spray kept in a container under pressure that is released in a fine spray when a button is pushed

confident – adj. a feeling or belief you can do something well

global – adj. involving the entire world

greenhouse gas – n. a gas in the atmosphere that absorbs and emits radiation, causing greenhouse effect and warming of Earth’s temperature



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