Shrinking ozone hole affecting climate.

• Position: Global Warming

The closing of the ozone hole, which is projected to occur sometime in the second half of the 21st century, significantly may affect climate change in the Southern Hemisphere and, there fore, the global climate, according to a study by researchers at Columbia University, New York.

The Earth's ozone layer is located in the lower stratosphere, which lies just above the troposphere (which begins at the planet's surface and reaches up to about 12 kilometers), catching harmful ultraviolet rays from the sun. Until late in the last century, widespread usage of household and commercial aerosols containing chlorofluorocarbons (CFC), unstable compounds which are carried into the stratosphere, led to significant and rapid ozone depletion. Due to the Montreal Protocol, signed by 191 countries, CFC production worldwide was phased out in 1996. Observations in the last few years indicate that ozone depletion largely has halted and is expected to reverse fully. As a consequence, the study finds, the Southern Hemisphere climate change also may reverse. This would be a very tangible outcome of the Montreal Protocol, which has been called the single most successful international agreement to date, and would demonstrate how international treaties are able to make positive changes to the climate system.

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In the past few decades, the tropospheric winds in the...