Scientists, politicians and businesses continue to debate the causes of global warming, with some arguing 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 greenhouse gases and the use of aerosols.
There is also controversy over how fast the Earth is warming up. Some scientists estimate that atmospheric temperatures could rise by 1.4°-5.8°C in the next 100 years. Others believe that they will rise more slowly.
Whatever the causes and timescale, the effects of global warming are very serious.