Enhanced Greenhouse Effect
The natural greenhouse effect keeps the Earth's surface much warmer than it would be if there was no atmosphere. Greenhouse gases in the atmosphere trap a lot of heat that would otherwise escape to space, raising the temperature. From the end of the last Ice Age episode about 10,000 years ago until the end of the 18th century, the levels of greenhouse gases in the atmosphere remained fairly constant. Since the Industrial Revolution 200 years ago, mankind has been releasing extra quantities of greenhouse gases into the atmosphere, which trap more heat, enhancing the natural greenhouse effect. The "enhanced" greenhouse effect is the direct result of human activities. Processes such as the burning of fossil fuels, industrial operations and forest clearing release carbon dioxide, methane and nitrous oxide into the atmosphere. Chlorofluorocarbons, or CFCs, are also potent greenhouse gases, and as an added danger, they also destroy the ozone layer.
Man-made emissions of carbon dioxide, more than any other greenhouse gas, have contributed most to the enhancement of Earth's natural greenhouse effect, about 60% since the late 18th century when man-made greenhouse gas emissions began to increase. Methane, nitrous oxide and the CFCs have contributed about 20%, 4% and 12% respectively.
During the 20th century, the Earth's surface warmed by about 0.6°C. Scientists have been speculating whether this global warming has been caused by the enhanced greenhouse effect. Climate models are used to detect a human fingerprint in the climate. As their reliability has improved, the link between greenhouse gas pollution and global warming has been strengthened.