Greenhouse gases are gases in an atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. Themain greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. In our solar system, the atmospheres of Venus, Mars and Titan also contain gasesthat cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth's surface would be on average about 33 °C (59 °F) colder than at present.
The burningof fossil fuels since the beginning of the Industrial revolution has substantially increased the levels of carbon dioxide in the atmosphere.
*Greenhouse gas emissions*
Measurements from Antarcticice cores show that before industrial emissions started atmospheric CO2 levels were about 280 parts per million by volume (ppmv), and stayed between 260 and 280 during the preceding ten thousandyears. Carbon dioxide concentrations in the atmosphere have gone up by approximately 35 percent since the 1900s, rising from 280 parts per million by volume to 387 parts per million in 2009. One studyusing evidence from stomata of fossilized leaves suggests greater variability, with carbon dioxide levels above 300 ppm during the period seven to ten thousand years ago, though others have argued thatthese findings more likely reflect calibration or contamination problems rather than actual CO2 variability. Because of the way air is trapped in ice (pores in the ice close off slowly to form bubblesdeep within the firn) and the time period represented in each ice sample analyzed, these figures represent averages of atmospheric concentrations of up to a few centuries rather than annual or decadallevels.
Recent year-to-year increase of atmospheric CO2
Since the beginning of the Industrial Revolution, the concentrations of most of the greenhouse gases have increased. For example, the...