Climate is the average pattern of weather over the long term. The earth's climate has warmed and cooled for millions of years, however we know that the earth has become warmer over the last century.
The Intergovernmental Panel on Climate Change (IPCC), reports in its Fourth Assessment Report (AR4) ‘Climate Change 2007’ that the average surface temperature of the earth has increased by an average of 0.74 oC ± 0.18oC between the years 1906 and 2005. (The ± 0.18oC means that the increase might be as small as 0.56oC or as great as 0.92oC). This may seem like a small shift, but although regional and short-term temperatures do fluctuate over a wide range, global temperatures are generally quite stable.
The World Meteorological Organisation (WMO) and United Nations Environment Programme (UNEP) established the Intergovernmental Panel on Climate Change (IPCC) to assess scientific, technical and socio-economic information relevant for the understanding of climate change, its potential impacts and options for adaptation and mitigation.
The difference between today's average global temperature and the average global temperature during the last Ice Age is about 5ºC. It is warmer today around the world than at any time during the past 1000 years, and eleven of the twelve years in the period (1995-2006) rank among the 12 warmest years in the instrumental record (since 1850, towards the end of the Little Ice Age).
The total volume of sea ice in the Arctic reached a record low last summer, raising fears that global warming may have tipped the Polar Regions into irreversible climate change far sooner than predicted. Scientists are now convinced that Arctic Sea ice is showing signs of both a winter and a summer decline that could indicate a major acceleration in its long-term rate of disappearance. According to NASA and the National Snow and Ice Data Centre (NSIDC) the most recent winter maximum reached on 28 February this year, was the fifth lowest since satellite records began in 1979 and meant the last six years were the sixth lowest on record.
The images below show the reduction in Arctic sea ice over a 29 year period. The image on the left shows the ice cover in September 1979. The image to the right shows the ice cover in September 2007.
We now know that human activities, primarily the burning of fossil fuels, have increased the greenhouse gas content of the earth's atmosphere significantly over the past century.
The 'greenhouse effect' is the rise in temperature that the Earth experiences because certain gases in the atmosphere (e.g. water vapour, carbon dioxide, nitrous oxide and methane) trap energy from the sun. Without these gases, heat would escape back into space and the Earth's average temperature would be about 60ºC colder. Because of how they warm our world these gases are referred to as greenhouse gases. The greenhouse effect is important as without the greenhouse effect, the Earth would not be warm enough for humans to live.
However if the greenhouse effect continues to get stronger and the density of greenhouse gases in our atmosphere increases, which can be caused by the increase in the amount of carbon dioxide emissions released from power generation using fossil fuels, it could cause the Earth to continue getting warmer than usual. The vast majority of climate researchers agree with these overall findings.
Carbon dioxide is one of the most important greenhouse gases, which traps heat near the earth’s surface. Global warming refers to an average increase in the Earth's temperature, which in turn causes changes in our climate. A warmer Earth may lead to changes in rainfall patterns, a rise in sea level, and a wide range of impacts on plants, wildlife, and humans. When scientists talk about the issue of climate change, their concern is about global warming caused by human activities, and is widely regarded as the most pressing environmental concern of this century.
Carbon dioxide (CO2) is responsible for two thirds of human-induced global warming - and around 97% of the CO2 emitted by western industrialised countries comes from burning coal, oil and gas for energy. Source WWF