Ozone Layer Hole
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Ozone depletion describes two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere (the ozone layer ), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions.  The latter phenomenon is referred to as the ozone hole . There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric events.