Scientists, politicians and industrialists continue to debate the causes of global warming, with some arguing that it is a natural process that's been going on for centuries. However, the Intergovernmental Panel on Climate Change (IPCC) - established by the United Nations in 1988 - has stated the evidence suggests that human activity does affect global warming, in particular through the release of greenhouses gases and the use of aerosols.
There is also debate over how quickly the earth is warming up. Some scientists estimate that atmospheric temperatures could rise by 1.4°C - 5.8°C in the next 100 years. Others believe that they will rise more slowly.
Whatever the causes and timescale, the implications of global warming are very serious.
The map above shows which countries are responsible for the most emissions. LEDCs want to develop and to catch up with MEDCs and this normally means using more energy and burning more fuel. So global warming could threaten development.
Global warming could melt the world's ice caps and glaciers, leading to an increase in sea levels. Some scientists estimate that over the next hundred years sea levels could rise by between 10 cm and 90 cm - making many coastal areas around the world uninhabitable.
Global warming could also affect the weather patterns, leading to more droughts, flooding and extreme weather, such as hurricanes.
In the UK we are largely unaffected by the dangerous weather of the tropics, such as hurricanes or severe droughts. But some climatologists argue that the UK climate is changing as a result of global warming, with the possibility of more frequent floods, water shortages, and extreme weather conditions.