STRATOSPHERIC OZONE DEPLETION

OZONE DEPLETION

Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon is referred to as the ozone hole. In addition to these well-known stratospheric phenomena, there are also springtime polar tropospheric ozone depletion events.

OZONE DEPLETION: AN INTRODUCTION

Planet Earth has its own natural sunscreen that shields us from the sun's damaging ultraviolet radiation. It's called the ozone layer: a fragile band of gases beginning 15 kilometers above our planet, and reaching up to the 40-kilometre level. Human activities have caused a substantial thinning of this protective covering — not only over the North and South Poles, but right over our heads.

Stopping ozone layer depletion is one of the major challenges facing the world today. The stakes are incredibly high. For the ozone layer is truly a "conserver of life," essential to the survival of all living things.

THE STRATOSPHERIC OZONE LAYER

The ozone layer lies in the stratosphere, in the upper level of our atmosphere. The ozone in it is spread very sparsely. In fact, if you could squish the ozone layer to the same air pressure we have at sea level, it would be only about as thick as the sole of your shoe.

Stratospheric ozone filters out most of the sun's potentially harmful shortwave ultraviolet (UV) radiation. This ozone has become depleted, due to the release of such ozone-depleting substances as chlorofluorocarbons (CFCs). When stratospheric ozone is depleted, more UV rays reach the earth. Exposure to higher amounts of UV radiation could have serious impacts on human beings, animals and plants.

DEPLETION OF THE STRATOSPHERIC OZONE LAYER (OZONE DEPLETION)

In 1985, a group of scientists made an unsettling discovery: a marked decrease in stratospheric ozone over the South Pole, in the Antarctic. The depletion appeared during the southern hemisphere's spring (October and November) and then filled in. Soon after the Antarctic hole was found, Canadian scientists discovered that the ozone layer above the Arctic is also thinning significantly.

The highest latitudes — the north and south poles — experience the greatest amount of ozone loss, during their spring. Ozone depletion is most pronounced in the Antarctic. But ozone depletion, to a lesser degree, now occurs in the mid-latitudes. For example, the amount of stratospheric ozone over the northern hemisphere has been dropping by 4% per decade.