Hole in the 'Zone

What's Eating the 'Zone

Scientists in the 1960s realized that something was going wrong in the ozone layer. They soon figured out that human actions were damaging Earth's shield against harmful radiation.


Close to Earth, CFCs were inert. That means the molecules didn't change. High in the atmosphere, however, ultraviolet (UV) radiation from the sun broke down the normally stable bonds in CFCs. This change released a chlorine atom that then destroyed the ozone (O3) by snatching away its third oxygen atom.

Click to view animation o3split_sm
  Source: UCAR

Very cold air temperatures over Antarctica sped the process. Ice crystals forming in the stratosphere gave CFCs a place to collect. When this air heated up in the springtime, the chlorine atoms were released by the ice crystals and reacted with the ozone. Each year the ozone hole became bigger, until it spread over Antarctica and across much of the Southern Hemisphere.

Yikes! Why were people destroying the ozone layer, the natural "sunscreen" we need to survive? The answer was our reliance on chlorofluorocarbons (CFCs), which people once thought were ideal chemical compounds. You could find CFCs in lots of things that helped us live better:

  Click to enlarge image
CFC  molecules.  Source: NASA
Chlorofluorocarbons (CFCs) contain carbon, chlorine, fluorine, and sometimes hydrogen.
Source: NASA
  • Refrigerators
  • Spray cans
  • Air conditioners
  • Styrofoam products
  • Insulation
  • Cleaning solutions

But we discovered that CFCs were "punching" holes in the ozone layer. Here's how the discovery was made, and what we did about it. Luckily, it's a story with a happy ending.


In 1974 three scientists in California said CFCs were harmless close to Earth, but that they suddenly became harmful when they reached higher levels in the atmosphere. The sun's ultraviolet radiation caused them to become chemically active, breaking down the ozone that protects life on Earth. (In 1995, these scientists won the Nobel Prize for chemistry.)

It was hard to measure the loss of ozone because there were no earlier measurements for comparison. Not using CFCs would have meant finding new ways to cool houses, insulate schools, and clean things. This would cost billions of dollars. So people argued whether it would be worth it.


CFCs still could be used in refrigerators, air conditioners, and cleaning solutions. But the spray can laws were an important start. Things settled down a bit until ...


  Click to enlarge image
The blue shape over Antarctica shows where strato<span>spheric ozone</span> has been depleted. Source: NASA
The blue shape over Antarctica shows where stratospheric ozone has been depleted.
Source: NASA: Ozone Measurements

In 1985 scientists reported in Nature, a well-respected British science journal, that there was a hole in the ozone layer above Antarctica. The hole over the Antarctic is seasonal, appearing in September (spring in the Southern Hemisphere) and lasting until early December. Each year, moreover, the hole grew larger. CFCs were blamed.

In 1989 world leaders met in Montreal, Canada, and agreed to reduce CFC production. The treaty is known as the Montreal Protocol. It worked! Scientists now are finding fewer CFCs in the stratosphere, and they are optimistic that the hole in the ozone layer might disappear in the next few decades.

There's still more work to be done, but it's good to know we really can solve problems if we put our energy into it.


science_iconHas the Montreal Protocol solved everything?


The source of the animated image in the sidebar is the Cooperative Program for Operational Meteorology, Education, and Training (COMET®) website of the University Corporation for Atmospheric Research (UCAR), funded by the National Weather Service. ©2002 University Corporation for Atmospheric Research. All Rights Reserved.


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