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The earth is getting warmer. The average global temperature has risen by about 0.6oC over the last century – probably the largest increase in any century in the last 1000 years (see the United Nations Environment Programme).
Natural processes cause temperatures around the world to change a little from one year to the next. However, most scientists believe that the rapid rise in temperatures over recent years, have been caused mainly by human activities.
So, why is the earth getting warmer?
The temperature of the earth is kept roughly the same by a balance of natural processes. Energy from the sun is absorbed by the earth and some of this energy helps to keep the planet warm enough to live on. However, a lot of the energy is re-radiated (or given out) from the earth's surface and the gases in the atmosphere and escapes into space. This keeps the temperature of the planet steady (in ‘equilibrium').
If human actions cause less energy to be re-radiated into space, then the surface temperature of the earth rises until equilibrium is reached at a new and higher temperature and we all get just a little bit warmer.
But there is a problem. Even a small average rise in temperature of just 1 or 2 degrees Celsius can have major effects on our planet: grasslands could turn into desert, the normal patterns of the wind, waves and currents may change, frozen seas may melt.
Melting ice is a particular problem. Not all the energy that reaches the earth from the sun is absorbed – a lot is reflected straight back into space. If large areas of snow and ice melt, the earth's reflectivity (or albeldo) decreases. More solar radiation is absorbed and temperatures increase. The knock-on effect is clear: higher temperatures melt even more ice and the entire cycle starts again.
Today governments are aware of the effects of climate change and many put it at the top of their political agenda. However, warnings from scientists that time is running out are becoming increasingly urgent.
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