5 Minute Guide: Climate change
Updated on 25 June 2007
Man-made global warming is the most important story of our age. Floods, droughts and famines are just the beginning. But some people claim it doesn't exist.
US President Lyndon Johnson was first warned about man-made global warming in 1965.
Since then awareness has spread from the scientific community to the environmental movement and now into mainstream politics as a whole.
Simply put, man-made global warming is happening because carbon dioxide (or, to use the shorthand term, carbon) is released into the atmosphere by the burning of fossil fuels.
Carbon dioxide in the atmosphere prevents energy from the sun's rays escaping back into space - trapping heat like the glass of a greenhouse, hence the name Greenhouse Effect.
Why does it matter?
Rising temperatures matter for several reasons: they affect rainfall patterns and make droughts more common. This is already affecting the developing world where, according to some estimates, there are already 200 million climate refugees.
Hotter temperatures cause ice on glaciers to melt. Melting ice will lead to a rise in sea levels, threatening to flood low-lying areas of the UK and other countries.
Some low-lying island states may be entirely submerged beneath the waves. A warmer planet also affects the habitats of animals.
Some scientists believe that rising temperatures may make extreme weather events more common, like Hurricane Katrina, which devastated New Orleans.
Most seriously, rising temperatures melt the ice on mountains, and at the poles. Some of the most dramatic evidence that global warming exists comes from pictures of mountain glaciers, which have shrunk massively or even disappeared over the past 40 years.
What happens next?
Climate campaigners are trying to persuade people to cut their emissions. But any climate solution needs the cooperation of governments.
The consensus is clear: the Earth is already getting hotter.
The best known example of this is the Kyoto Protocol, agreed in 1997, which commits developed countries to cut their greenhouse gas emissions. Yet the protocol did not initially have the support of the US, China and India - three of the world's biggest polluters.
The fear with global warming is that the Earth will reach a tipping point, where the warming process gets out of control.
For example, snows in the Arctic help to cool the Earth by reflecting heat into space, like a mirror. If they disappear, the Arctic will start to warm even more rapidly.
There is endless debate among scientists about the detail, but they agree on the basics. Bar a few eccentric deniers, the consensus is clear: the Earth is already getting hotter, and will continue to do so if mankind doesn't stop pumping out ever-increasing amounts of carbon dioxide.
Through their consumption, people in the West, particularly in America, pump out far more greenhouse gasses than those in developing countries.
Climate change campaigners are calling on everyone to modify their lifestyles to cut their CO2 and reduce their carbon footprint.
This means driving less, flying less, consuming less. Even small measures are a step in the right direction, such as using energy efficient lightbulbs and not leaving appliances on standby.
The US, the world's biggest polluter has agreed to consider cutting emissions by 50 per cent by 2050 - but many obstacles remain, not least the agreement of India and China.
The developing world
Consumers in the developing world produce on average far less carbon dioxide than their Western counterparts. But many aspire to match Western lifestyles, and are catching up fast.
If everyone in China and India has a car, a television and a fridge, then no amount of low-energy lightbulbs in Surbiton will make up for the carbon dioxide they pump out. And who's going to tell them they aren't allowed?
After eight years as Bill Clinton's vice president, and the narrow election defeat to George W Bush in 2000, Al Gore has a new mission: to educate the world about climate change.
His film An Inconvenient Truth is a good primer on global warming, and has made him a leading voice in the climate change debate. As a possible runner for the 2008 presidential elections, who better than a politician to lead the fight against hot air?