The so-called "Ozone Hole" is a gap in the ozone layer which appears each Southern hemisphere spring in the lower stratosphere above the South Pole. If you want to know more about the Ozone Hole please use The Ozone Hole Multimedia Tour provided by our Centre for Atmospheric Science.

The horizontal extension of such an ozone hole can be seen in the following picture of a measurement by the TOMS satellite on 3rd October 1994.

The colours indicate the total ozone column amount above any given point on the surface of the Earth in units of DU (for information on DU, or Dobson Units, please click here). The ozone hole can be seen to extend above the whole of Antarctica and beyond.

The vertical extension of the ozone hole is as shown on the following picture.

The vertical distribution of ozone straight above the South Pole is depicted for 4 different dates in 1993, indicating the build up of the 'hole' in the ozone layer during Antarctic spring time. In October, the ozone between 14 and 19 kilometres height has totally vanished reducing the total ozone column amount to 88 DU.

Ozone does absorb strongly in the UV light in a wavelength around 300nm (the so-called UVB light), as well as in the visible. The fact that ozone does absorb UVB light so strongly makes life on Earth possible in that an intact ozone layer is fully absorbing all UVB light from the sun, and hence is protecting life from this highly damaging radiation. I used the above data on ozone to calculate how much UVB light is coming through to the Earth's surface underneath an ozone hole to give an indication of the danger to life.

This picture shows radiation intensity [erg/sec/cm*cm] versus wavelength [nm] underneath the ozone hole in 1992 minus the radiation intensity underneath an intact ozone layer (solid curve). In other words, the curves show the amount of UVB radiation coming through underneath an ozone hole, given that almost all UVB is absorbed with an intact ozone layer. The dashed curve shows the same for the ozone hole in 1987. It is apparent that the solar UVB radiation is coming through with an alarming intensity, and - even more alarming - rapidly increasing as the ozone hole is deepening over the years. Underneath the 1992 ozone hole the UVB radiation was almost twice as strong as underneath the 1987 ozone hole. Underneath the 1992 ozone hole, already two thirds of the whole solar UVB radiation is reaching the Earth's surface.

This picture shows again the difference between the radiation intensity [erg/sec/cm*cm] versus wavelength [nm] underneath the 1992 ozone hole and an intact ozone layer. However, as the sun is at different zenith angles over the day, this picture shows the variation of this difference with the solar zenith angle. The solid curve shows the (unrealistic) scenario of an overhead sun, the dashed curve for a sun at 60 degrees zenith angle, the dotted curve for a sun at 80 degrees, and the dash-dotted curve for a sun at the horizon. It is apparent that the amount of UVB radiation reaching the Earth's surface decreases with increasing solar zenith angle. In contrast, the visible part of the spectrum has an increased amount of radiation coming through with increasing solar zenith angle. This is the reason why a sunset (or sunrise) looks very different underneath an ozone hole or underneath an intact ozone layer (see sunset simulations in the Earth's atmosphere within and outside an ozone hole).

As we know, the increase in UVB radiation due to ozone loss is very damaging to complex molecules, which are an essential ingredient for life as we know it. However, it has been argued that there are no (important) living beings underneath this ozone hole over the Antarctic anyway. While there actually are sentient living beings there, like penguins for example, even the most anthropocentric self-centred human must admit that the impact of increased UVB will be devastating to life on Earth in general, as shown by the following picture.

Furthermore, there is a general decrease in ozone in midlatitudes with a downward trend of currently 0.8% per year. In addition, the Northern spring time vortices above the North Pole in the last years have shown that in the Northern hemisphere substantial ozone loss can occurr as well. The latter is then indeed above parts of the Earth inhabited by humans.