The ozone layer is recovering

One of the worst environmental catastrophes was just averted: Current measurements confirm that the ozone layer is thickening again. The increase in carcinogenic UV radiation has thus been stopped. But it is still too early to sound the all-clear.

The new measurement data sound encouraging: exposure to UV radiation is declining. Up to 4% less of the harmful UVB rays reach the earth. Twelve measuring stations in Europe, Canada and Japan were evaluated for this purpose. This good news is the result of successful environmental policy. In the Montreal Protocol of 1987, measures were agreed to protect the ozone layer. These included the gradual ban of the destructive chlorofluorocarbons, or CFCs. Since then, the concentration of CFCs in the air has been gradually decreasing. The ozone layer can recover very slowly.

However, skin should still be well protected. Sun creams with a medium to high sun protection factor are still beneficial. Scientists warn that radiation levels are still high, especially in spring. This is because CFCs degrade only very slowly. It becomes really aggressive when it is very cold. Over the poles, the ozone layer is therefore still very thin. If the polar air masses move as far as Europe in late winter and spring, the effects of the ozone hole will also be felt in this country. Especially on these days, there is an increased risk of sunburn.

Despite falling CFC levels, a hole in the ozone layer was discovered for the first time over the Arctic in 2011. Experts say the reason for this is climate change: On the ground, the temperature is rising, but the stratosphere is cooling. As a result of the falling temperatures, the ozone in the upper layers of the air would deplete more quickly.

The discovery of the ozone hole

In May 1985, an article in the magazine “Nature” shook the public awake: “Severe loss of total ozone in Antarctica” was the headline. British researchers had discovered a huge hole in the ozone layer over the South Pole, as big as the entire Antarctic. One of the three authors of the article was the geophysicist Joseph Farman, who is now considered the discoverer of the ozone hole. He had evaluated the measurements above the Antarctic station over a long period of time.

For quite a while, there had been indications that the ozone layer was disappearing, but these were simply dismissed as measurement errors. The publication of the article, however, set off an alarm signal that no one could ignore any longer. The international community reacted: in 1987, it was decided in the so-called Montreal Protocol to phase out the ozone killer chlorofluorocarbon.

Ozone hole

High up in the stratosphere, the ozone layer protects us from harmful UV rays. If it didn’t exist, the sun’s radiation on the ground would literally roast us. Life in its present form would not be possible at all without this protective shield.

But the ozone layer has developed dangerously large holes. The reason for this are chemical substances that humans have blown into the atmosphere. The biggest enemy of ozone is chlorofluorocarbon, or CFC for short. For a long time, this gas was used as a coolant in refrigerators and as a propellant in spray cans. In itself odourless and non-toxic, CFCs only become dangerous to humans when they rise: In the stratosphere, it reacts with ozone, thus attacking and destroying the ozone layer.

But if the UV radiation is no longer shielded by the ozone layer, it damages life on this planet. We get sunburned much faster and have to use stronger and stronger sunscreens. In the worst case, skin cancer is the result of the unfiltered radiation. The eyes are also severely affected; without the ozone layer we would go blind. People in Australia and New Zealand are particularly affected, because it is in their vicinity – above Antarctica – that the ozone hole is largest. The ozone layer is also thin over the North Pole because the ozone is broken down more quickly in extreme cold.

If the UV light reaches the earth unhindered, another problem arises: unicellular plants die on the surface of the sea – the phytoplankton. However, this plankton is very important for us because it supplies oxygen and consumes carbon dioxide in the process.

Fortunately, scientists have recognised the connection between CFCs and the hole in the ozone layer. Politicians also reacted just in time. The ozone killer CFC is now banned worldwide. Very slowly, the ozone layer is recovering. However, it will take several years before it is completely healthy again, because CFCs are very stable. It decomposes only slowly and the gases are still on their way up. There they can continue to attack the ozone layer for over a hundred years.

Ozone layer

It happens far above our heads, about 15 to 35 kilometres up in the stratosphere: here, the energy of the sunlight splits the oxygen into its two oxygen atoms. The individual oxygen atoms react with each other and can also come together in threes. When this happens, ozone molecules are formed.

Because ozone is concentrated in the stratosphere, a layer forms here: the ozone layer. This blocks a large part of the sun’s rays and prevents too much ultraviolet radiation from reaching the earth. This is vital, because the sun’s high-energy ultraviolet rays can destroy the cells of animals and plants and damage human skin. If the stratospheric ozone layer is intact, it acts like a huge protective screen against aggressive UV radiation.

Especially on hot summer days and in heavy traffic with lots of exhaust fumes, ozone can also be formed close to the earth’s surface. Down here, however, the gas is not useful but harmful: it can cause headaches, fatigue and burning eyes and attack the respiratory tract. If the ozone content at ground level exceeds a certain value, ozone warnings have been issued on radio, television and the Internet for some years. Physical exertion outdoors should then be avoided.

The layers of the atmosphere

Similar to the storeys of a multi-storey house, the atmosphere is divided into several layers. These layers have different properties – let’s start with the “ground floor”:

Whether dark storm clouds or blue skies, gentle breezes or strong winds: almost all weather events take place up to an altitude of 15 kilometres. This lower layer of the atmosphere is therefore also called the weather layer. Scientists call it the troposphere. About 90 percent of all the air and almost all the water vapour in the Earth’s atmosphere is contained in this layer. The higher it is in the troposphere, the colder it gets: Icy temperatures of up to minus 80 degrees Celsius prevail at its upper limit.

In the layer above, the stratosphere, the temperature suddenly rises again. At an altitude of about 50 kilometres, the thermometer even reaches a value around 0 degrees Celsius. The reason for this warming is the ozone layer that lies within the stratosphere. It acts like a heater: it absorbs the UV radiation of the sun and converts it into heat.

Above the stratosphere, at an altitude of 50 to 80 kilometres, lies the mesosphere. Because this layer contains no ozone, it gets bitterly cold again, down to minus 100 degrees Celsius. This makes the mesosphere the coldest layer of the atmosphere. This is where dust particles and smaller rock fragments from space are trapped, which would otherwise crash to Earth as meteorites. We can sometimes see these celestial bodies in the sky at night as shooting stars.

Above the mesosphere, the air becomes thinner and thinner. The Earth’s gravitational pull weakens with increasing altitude and can therefore hold the gas particles less and less. Thus, the thermosphere forms a smooth transition into space over hundreds of kilometres. The thermosphere gets its name from the high temperatures that prevail here: they rise up to 1700 degrees. However, it is not hot according to our imagination, because there are too few gases buzzing around for it to feel hot.

A shell of gas

Seen from space, it appears like a fine bluish veil that wraps around the Earth: the atmosphere. It is the envelope of air that surrounds our planet. Compared to the diameter of the Earth, this envelope is quite thin: if the Earth were the size of an apple, the atmosphere would be about the thickness of its skin.

Without the atmosphere, there would be no life on this planet, because plants, animals and humans need air to breathe. It protects us from the cold and from harmful radiation from space. It also allows meteorites to burn up before they can hit the earth’s surface. This air envelope is vital for us – but what is it actually made of?

The atmosphere is a mix of different gases. A large part of this gas mixture is nitrogen: at 78 per cent, this is almost four-fifths of the entire atmosphere. Only 21 percent consists of oxygen, which we need to breathe. The remaining one percent is made up of various trace gases – gases that only occur in the atmosphere in traces. These trace gases include methane, nitrogen oxides and, above all, carbon dioxide, or CO2 for short. Although the proportion of CO2 is quite small, this trace gas has a huge influence on our earth’s climate. This can be seen in the greenhouse effect, which heats up our planet.

The fact that the Earth has an atmosphere at all is due to gravity. It holds the gas molecules on the earth and prevents them from simply flying out into space. In fact, the air becomes thinner and thinner with increasing altitude and thus decreasing gravity. At altitudes as low as 2000 metres above sea level, this can become unpleasantly noticeable for people: They suffer from altitude sickness with shortness of breath, headaches and nausea. Extreme mountaineers who want to climb high peaks like the 8,000-metre peaks of the Himalayas therefore usually take artificial oxygen with them on their tour.