|
Climate changes for many reasons. Changes in solar energy, increased greenhouse gas concentrations, volcanic eruptions, and the El Niño phenomenon, all affect Earth's temperature. Variances in rain and snowfall accompany changes in temperature. Human activities have increased greenhouse gas concentrations in the atmosphere. At Barrow, Alaska, atmospheric carbon dioxide concentrations have increased steadily since the 1970's. Across Alaska, temperatures rose abruptly in 1976 and have remained high, and the extent of sea ice in the Bering Sea has decreased. Increased greenhouse gas concentrations are thought to be a major cause of the global warming observed over the last 100 years. Climate models predict further warming with continued increases in greenhouse gas concentrations.
Most of the Arctic has warmed over the last 30 years, particularly over large land masses. Shown below are the mean observed annual temperature increases per decade from meteorological observations. Warming in winter has been even greater than trends shown here.
 |
Gases that trap heat radiated from Earth's surface are commonly called "greenhouse gases." Carbon dioxide, methane, nitrous oxide, and water vapor occur naturally in Earth's atmosphere and make Earth's temperature warmer than it would be if they were not present. The atmospheric concentration of these gases has increased since the industrial revolution. Other gases introduced by humans, such as chlorofluorocarbons (CFC's), also act as greenhouse gases.
|
[ Global Warming Home ]
[ BESIS ]
|