Impacts on the world
The clearest evidence of current global warming comes from the world's mountain ranges, where glaciers are melting everywhere. Also melting fast are some parts of the earth's polar regions. The Antarctic Peninsula is the most rapidly warming area of the planet, and the Larsen B ice shelf on the peninsula's eastern edge - a floating shelf the size of Luxembourg - collapsed dramatically in 2002.
On the other side of the world, the Arctic is, according to a 2004 landmark report called the Arctic Climate Impact Assessment (ACIA), experiencing "some of the most rapid and severe climate change on earth." Snow cover has declined by 10 per cent over the past 30 years, and melting permafrost is destroying buildings and forests alike. Summer sea ice extent has declined by a fifth in the past three decades, and the 2002 ice melt on Greenland broke all records.
Melting land ice combines with thermal expansion of the oceans to cause sea level rise, which is now having a visible impact on vulnerable Pacific atolls like Tuvalu, whose people now suffer annual bouts of flooding. Coastal erosion is also an increasing problem, and 70 per cent of the world's sandy shorelines are now retreating.
Saltwater intrusion into low-lying areas has been documented as far afield as China's Yangtze delta and Australia's Mary river. According to satellite monitoring systems, the rate of sea level rise has recently begun to accelerate, and has now reached 2.8mm per year.
The expected result of an increase in global temperature is an increase in extreme weather as the planetary hydrological cycle speeds up. More rainfall is now recorded in higher latitudes, whilst droughts are more profound in the arid sub-tropics. Heatwaves have killed increasing numbers of people: upwards of 30,000 perished in Europe during the blistering summer of 2003.
Although caution needs to be exercised in linking specific events to climate change, a statistical analysis of the 2003 summer heat wave by Peter Stott of the Hadley Centre for Climate Prediction, published in Nature, showed that human greenhouse gas emissions made it twice as likely.
In 2004, there was a very active Atlantic hurricane season, with a record four storms ploughing into Florida - whilst a tropical cyclone also formed for the very first time in the south Atlantic, hitting Brazil. However, the eastern Pacific saw a below-average number of storms.
Already climatic change has begun to alter the distribution of certain species. For example, it has enabled birds like cattle egret to extend their range northwards. Two worldwide studies published in 2003 found evidence of changes in wildlife behaviour ranging from earlier frog breeding and the arrival of migrant birds to a general move towards the poles for butterflies, fish and hundreds of other plant and animal species. In most cases the changes have been damaging: hundreds of thousands of Scottish seabirds failed to raise young during the 2004 breeding season due to a collapse in the numbers of sand eels, the birds' main food source - itself related to a shift north of cold-water plankton.