The natural greenhouse effect keeps the Earth 30 °C warmer than it otherwise would be.
Adding carbon dioxide to the atmosphere, with no other changes, will makes our planet's surface warmer.
Current research is attempting to find out more details about the processes and factors that would affect a temperature increase to allow a more precise quantification of the effects of global warming.
Global warming is an increase in the average temperature of the Earth's atmosphere and oceans.
The term is also used for the scientific theory of anthropogenic global warming, which attributes much of the recently observed and projected global warming to a human-induced intensification of the greenhouse effect.
On this theory, the increased volumes of carbon dioxide and other greenhouse gases released mainly by the burning of fossil fuels, and, to a lesser extent, land clearing and agriculture, are the primary sources of warming.
Uncertainties do exist regarding how much climate change should be expected in the future, and a hotly contested political and public debate exists over what actions, if any, should be taken in light of global warming.
Based on basic science, observational sensitivity studies, and the climate models referenced by the IPCC, temperatures may increase by 1.4 to 5.8 °C between 1990 and 2100.
This is expected to result in other climate changes including rises in sea level and changes in the amount and pattern of precipitation.
Such changes may increase the frequency of extreme weather events such as floods, droughts, heat waves, and hurricanes, change agricultural yields, or contribute to biological extinctions.
Over the past century or so the global (land and sea) temperature has increased by 0.6 ± 0.2 °C]. The effects of global warming are increasingly visible.
At the same time, atmospheric carbon dioxide has increased from around 280 parts per million (by volume) in 1800 to around 315 in 1958 and 367 in 2000, a 31% increase over 200 years. Other greenhouse gas emissions have also increased.
Future carbon dioxide levels are expected to continue rising due to ongoing fossil fuel usage, though the actual trajectory will depend on uncertain economic, sociological, technological, and natural developments.
The IPCC SRES gives a wide range of future carbon dioxide scenarios, ranging from 540 to 970 parts per million by 2100.
Coal-burning power plants, vehicle exhausts, factory smokestacks, and other waste vents of the human environment contribute about 22 billion tons of carbon dioxide and other greenhouse gases into the earth's atmosphere each year. Animal agriculture, manure, natural gas, rice paddies, landfills, coal, and other sources contribute about 250 million tons of methane each year and about half of human emissions have remained in the atmosphere.
The atmospheric concentrations of carbon dioxide and CH4 have increased by 31% and 149% respectively above pre-industrial levels since 1750.
This is considerably higher than at any time during the last 650,000 years, the period for which reliable data has been extracted from ice cores.
From less direct geological evidence it is believed that carbon dioxide values this high were last attained 40 million years ago. About three-quarters of the anthropogenic emissions of carbon dioxide to the atmosphere during the past 20 years is due to fossil fuel burning.
The rest is predominantly due to land-use change, especially