About climate change
"The scientific evidence is now overwhelming. Climate change presents very serious global risks, and it demands an urgent global response"
Stern Review Report on the economics of climate change,
HM Treasury, UK Government, 2007
It has been getting hotter everywhere for some time. All of the 10 highest average global temperatures since reliable records began in 1880 have come since the 1980s. The temperature rose more in the 20th century than at any other time in the millennium; the 1990s were the warmest decade of the millennium.
There have been other climate changes, especially in rainfall - more heavy rain, causing floods. But at the same time we have also seen more droughts in other areas. These effects are not necessarily continents apart. For example, the UK and the US have been experiencing flooding in some regions and drought in others.
Higher temperatures mean less ice and more water. Greenland's ice sheet lost 224 cubic kilometres in 2005. There is still a lot to go - more than 2.8 million cubic kilometres - but the rate at which it is disappearing seems to be speeding up. Glaciers have been melting in countries as diverse as Canada, China and Peru. Melting ice means more water in the oceans, but the main reason sea levels have been rising (by 1 to 2mm a year during the 20th century) is that water expands as it warms.
The weather forecast is for more of the same. Average temperatures are expected to continue rising, perhaps by 6ºC during this century. The reason is that there is a lot more carbon dioxide (CO2), methane and other 'greenhouse gases' in the atmosphere than at any time since prehistory. Much of the CO2 has come from burning coal, oil and gas, while destruction of forests has made matters worse. Expansion of agriculture has also pushed more methane into the atmosphere, especially from belching cows.
Even if we manage to reduce emissions quickly, warming (and its consequences) will continue for many years because the carbon dioxide in the atmosphere will not go away quickly.
The effects are also unpredictable because we still have limited understanding of complex climate interactions - ocean temperatures affect currents, which influence air flows, which determine rainfall, and so on. The effects are unlikely to be uniform: some areas will be hotter and drier, others will be cooler and wetter; there may be more rain in winter and less in summer - or vice versa.
Climate change presents a significant challenge to the international community but at the same time there are also enormous opportunities if everyone is willing to take action. Government, business and individuals all have a part to play.
Climate change affects all of us - and we can all be part of the solution.