Global warning

PUBLISHED : Saturday, 02 September, 2006, 12:00am
UPDATED : Saturday, 02 September, 2006, 12:00am

THE atmosphere is a swathe of air that protects us from the sun's harmful rays and traps enough warmth to keep temperatures from falling too low at night.

Analysis shows the atmosphere consists of 78 per cent nitrogen, 21 per cent oxygen and 1 per cent other gases. It also contains water vapour.

While the atmosphere reaches more than 1,000km above the Earth's surface, some 72 per cent of its mass is below 10,000 metres - the height at which commercial aircraft fly.

Layers of protection

The atmosphere has special zones, each with its own characteristics. A standard method of reference recognises four layers that are defined by temperature, plus an outer layer called the exosphere.

The troposphere is the layer that lies closest to the Earth's surface. The temperature in this layer falls with altitude. The troposphere contains about 75 per cent per cent of the total mass of the atmosphere and is on average 12km high. All weather phenomena such as rain occurs here.

Above this lies the stratosphere, an area where temperatures rise the higher you go. The stratosphere is about 38km thick, reaching an average height of 50km above the Earth's surface. Planes often fly along the bottom of this layer. The stratosphere is also the home to 90 per cent of the ozone layer, a band of gas above the Earth's surface that filters out dangerous solar particles such as ultraviolet light. Ten per cent of the ozone layer is in the troposphere. Without this protective cover, radiation would damage and kill plants, and cause health problems such as skin cancer.

The mesosphere spans some 30km, lying between 50km and 80km above the surface of the Earth. Characterised by temperatures that fall quickly with height, this region is famous for its noctilucent clouds. These coloured clouds made of water vapour and bits of meteor that have burned up while entering Earth's atmosphere can be seen best at twilight.

The thermosphere, known as the upper atmosphere, is marked by rapid temperature gains as altitude increases. When particles from the sun disturb this region, a beautiful display of lights called the aurora borealis or aurora australis can be seen from the Earth, depending on whether you are in the northern or southern hemisphere. This is also the area satellites travel in.

Beyond the atmosphere is the exosphere, which starts about 450km above the Earth and has such a thin atmosphere that temperature readings cannot be taken. Home to dangerous ultraviolet radiation and lots of meteor dust, this layer is recognised as the start of space.

Vanishing security

Life on Earth could not exist without the protection provided by the atmosphere, yet modernisation is damaging this security blanket. Burning fossil fuels (such as coal, oil and gas) for energy and modern manufacturing and farming methods create lots of carbon dioxide, methane, and nitrous oxides - substances nicknamed greenhouse gases because they trap heat.

Studies show that the level of greenhouse gases in the air is high. In addition to man-made pollutants like chlorofluorocarbons, carbon dioxide levels are increasing 200 times faster than at any time in the past 650,000 years. As the delicate balance of gases in the atmosphere changes, the climate on Earth changes too.

When the level of gases increases, more heat is shut in, causing global temperatures to rise. Even if temperatures increase by just a few degrees, the effects are tremendous. We are already seeing deserts expanding, polar regions contracting, seas enlarging and whole ecosystems dying.

Cleaning up

While it has been recognised for decades that the Earth's security blanket works best when it's clean, the drive to reduce pollution has been slow. But now the climate change is visible, and the price of oil has climbed dramatically, attitudes are changing.

One way to reduce smog is to stop using fossil fuels and switch to wind power and other energy sources. Trials to make these sources of power efficient are receiving more attention - and more funding.

While scientists are figuring out new and clean ways to provide power, you can do your bit by switching off air conditioners, using energy-saving light bulbs and by walking or cycling instead of asking someone to drive you.