Hole Shrinkage Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, but the past use of chlorofluorocarbons (CFCs) in aerosols and other products has thinned the protection. The damage is embodied by the infamous “ozone hole” that forms over the South Pole every Antarctic spring. (A hole is defined as a thickness of ozone less than 220 Dobson units—or less than 2.2 millimeters thick if the ozone resided at sea level at 0 degrees Celsius.) Measurements of the hole taken by the European Space Agency’s Envisat satellite do not necessarily mean that the ozone layer has begun recovering. Rather weather patterns allowed warm air to mix into the polar regions, thus limiting the problem. Temperature below which ozone depletion occurs: –78 degrees C Percent that the ozone layer has thinned every year this decade: 0.3 Peak Antarctic ozone loss, in metric tons: In 2006: 40 million In 2007: 27.7 million Minimum ozone depth in hole, in Dobson units: In 2006: 100 In 2007: 120 Area of hole, in square kilometers: In 2006: 28 million In 2007: 24.7 million Area of North America, in square kilometers: 24.25 million SOURCE: European Space Agency announcement, October 3

Ozone in the stratosphere blocks deadly ultraviolet rays from the sun, but the past use of chlorofluorocarbons (CFCs) in aerosols and other products has thinned the protection. The damage is embodied by the infamous “ozone hole” that forms over the South Pole every Antarctic spring. (A hole is defined as a thickness of ozone less than 220 Dobson units—or less than 2.2 millimeters thick if the ozone resided at sea level at 0 degrees Celsius.) Measurements of the hole taken by the European Space Agency’s Envisat satellite do not necessarily mean that the ozone layer has begun recovering. Rather weather patterns allowed warm air to mix into the polar regions, thus limiting the problem.

Temperature below which ozone depletion occurs: –78 degrees C

Percent that the ozone layer has thinned every year this decade: 0.3

Peak Antarctic ozone loss, in metric tons:

In 2006: 40 million

In 2007: 27.7 million

Minimum ozone depth in hole, in Dobson units:

In 2006: 100

In 2007: 120

Area of hole, in square kilometers:

In 2006: 28 million

In 2007: 24.7 million

Area of North America, in square kilometers:

24.25 million

SOURCE: European Space Agency announcement, October 3