Since the Industrial Revolution 200 years ago, the amount of greenhouse gases in the air has been increasing. This is thought to be due to human activities. During the last fifty years mankind has also introduced CFCs, which not only damage the ozone layer but also act as greenhouse gases. Greenhouse gases also include carbon dioxide, methane, and nitrous oxide.
Carbon Dioxide
Carbon dioxide (CO2) is produced naturally through breathing or respiration, decay of plant and animal matter, and from natural forest fires. Man-made sources of carbon dioxide include the burning (or combustion) of fossil fuels, changes in land-use (especially deforestation), biomass
burning and the manufacture of cement. Carbon dioxide is taken out of the atmosphere by the
oceans, and by plants, especially forests, through photosynthesis.
Methane
Methane (CH4) is a major greenhouse gas. It is formed naturally in wetlands when organic material decays, and also by termites. Man-made sources of methane include the growing of rice, cattle farming, fossil fuel burning and the disposal of household waste in landfill sites.
Nitrous Oxide
Nitrous oxide (N2O) is a greenhouse gas naturally produced by oceans and by lightning strikes, but humans have increased its abundance by the production of nylon, nitric acid, and through agricultural practices and biomass burning.
Chlorofluorocarbons
Chlorofluorocarbons (CFCs) are a group of man-made substances containing chlorine, fluorine and carbon. They were invented in the 1930s for use in fridges, but have other uses, including aerosols.
Summary
The main human contribution to enhancing the greenhouse effect and global warming has been made by carbon dioxide, but more recently the CFCs have also had a large impact. CFC production has now been limited to protect the ozone layer, and so it is thought that
their effect on global warming will become less in the future.