The climate has always been fairly unpredictable, but there are some definite long term patterns in its behaviour - regular cycles of warmer and colder weather. During the coldest spells, for example, ice sheets have advanced over much of northern Europe. During the warmer cycles, the ice retreats. Now, however, the vast majority of scientists think current changes to our climate - and those predicted to occur over the next 100 years or so - are mainly due to our own activities rather than any natural cycle. It comes down to something called global warming...
The underlying problem is that we are burning coal, oil and gas - these fossil fuels contain huge amounts of carbon that has remained locked up beneath the ground for millions of years. Now it is suddenly being released into the atmosphere as carbon dioxide. Too much CO2 in the air is a bad thing - not because we'll choke on it (there's not nearly enough for that) - but because it alters the way the atmosphere of our planet behaves.
The Earth's atmosphere is like a huge window around the planet - sunlight can come in and warm the surface and this window helps trap some of that heat. At the same time the window also lets some heat escape into space. This is called the greenhouse effect, and it is this balance that maintains comfortable temperatures on earth. However it's a fragile balance - if the atmosphere traps just a little too much heat, the planet will slowly start to warm up.
Carbon dioxide is very good at trapping heat, which is why it's known as a greenhouse gas. Unfortunately for us, all the CO2 released by burning oil, coal and gas is acting like double glazing: the more we pump out into the atmosphere, the more heat is trapped on earth, and the warmer we get. If we carry on releasing extra CO2 from cars, planes, factories and power stations, an international panel of experts predict that the planet could warm up by several degrees during the next century.
Heading for Meltdown
This might not sound to bad, but even a small temperature rise could have catastrophic effects. Just an increase in average temperature of two or three degrees and the ice caps at the Arctic and Antarctic will begin to melt. If nothing is done, the icecaps could eventually release huge amounts of fresh water into the oceans. Sea levels could rise by many metres, drowning low-lying land and causing flooding. This could also change the way ocean currents flow. And since these currents help carry heat around the planet, any change could affect the weather, increasing rainfall in some areas and causing drought in others.
Many scientists believe our climate could have a tipping point - a point of no return at which changes will suddenly start to accelerate. For instance, the huge sheets of ice at the poles help reflect heat back into space. As these sheets melt and shrink, global warming will accelerate, so the ice sheets get smaller still. This could also release huge amounts of methane gas locked up in the frozen ground in the Canadian and Russian Arctic. Methane is like CO2 - it's a greenhouse gas - so the planet will warm even faster. This will release even more methane and so on. Suddenly the cycle becomes unstoppable. We're not going to see the overnight catastrophe predicted in the movie The Day After Tomorrow. These changes could take decades. Nevertheless, we should be seriously worried, for our children's sake, and take action now to prevent it happening.