What is Global Warming ?
In the atmosphere, a tiny number of gases like carbon dioxide, oxides of nitrogen and methane are able to trap heat around Earth. This is good news for all of us, as in the right thickness they act like a blanket and stop heat from leaving Earth. Scientists call this trapping of heat the greenhouse effect, because these gases work a bit like the glass in a greenhouse on a sunny day. The glass traps heat from the Sun and produces a temperature difference between the inside and outside. If we did not have the greenhouse gases in the atmosphere, the Earth’s average temperature would be around -18ºC, which is too cold for life to cope in those conditions.
There are six greenhouse gases in the atmosphere:
Ozone – This is a helpful gas in the layer of Earth’s atmosphere called the stratosphere, but it is dangerous when it forms in the troposphere. It forms there when sunlight reacts with exhaust fumes from trucks and cars.
Water vapour – Water vapour comes from surface water, and from animal and plant respiration. It is the Earth’s most common greenhouse gas and clouds are responsible for about 97% of the natural greenhouse effect.
Methane – This gas is released when bacteria break down organic matter. It’s given out by rotting plants (swamps, marshes and rice paddy fields), rubbish (landfill sites), animals as a waste gas and by burning fossil fuels. Methane can stay in the for atmosphere 12 years.
CFCs – These are used in refrigeration and at one time in aerosol sprays. CFCs can remain in the atmosphere for 1000 years.
Nitrous oxides – Nitrous oxides can form the burning of fossil fuels and is the most powerful greenhouse gas as it can trap around 270 times more heat than the same amount of carbon dioxide (CO2).
Carbon dioxide – This gas comes from volcanic eruptions, the burning of fossil fuels and wood and from plant and animal respiration. CO2 can stay in the atmosphere for up to 200 years.
However, many scientists believe that over the last 200 years, we have started to change the climate by accident through the burning of enormous amounts of coal, oil and gas. This has produced more `greenhouse' gases in the atmosphere and is causing the blanket to become thicker and so the Earth is slowly getting warmer.
Global warming is the name given to the noticeable rise in average temperature of the Earth as a result of human activity. Although the actual temperature rise might seem small (only a few Global Warming degrees over the next century), the Earth’s natural balance is very sensitive, so even this small increase in average temperature can cause major changes to weather patterns.
When weather patterns change the kinds of plants and animals which are able to survive also change and some species may even die out altogether. As plants, in particular, have their own influence on local weather patterns, this may cause yet more weather changes, and so the effects become greater and greater.