Global Warming is the phenomenon of increasing average air temperatures near the surface of Earth over the past one to two centuries.
Since the mid-20th century, climate scientists have gathered detailed observations of various weather phenomena (such as temperature, precipitation, and storms) and of related influences on climate (such as ocean currents and the atmosphere’s chemical composition). These data indicate that Earth’s climate has changed over almost every conceivable timescale since the beginning of geologic time and that, since at least the beginning of the Industrial Revolution, the influence of human activities has been deeply woven into the very fabric of climate change.
During the second half of the 20th century and early part of the 21st century, global average surface temperature increased and sea level rose. Over the same period, the amount of snow cover in the Northern Hemisphere decreased.
The Keeling Curve, named after American climate scientist Charles David Keeling, tracks changes in the concentration of carbon dioxide (CO2) in Earth’s atmosphere at a research station on Mauna Loa in Hawaii. Although these concentrations experience small seasonal fluctuations, the overall trend shows that CO2 is increasing in the atmosphere.
A series of photographs of the Grinnell Glacier taken from the summit of Mount Gould in Glacier National Park, Montana, in 1938, 1981, 1998, and 2006 (from left to right). In 1938 the Grinnell Glacier filled the entire area at the bottom of the image. By 2006 it had largely disappeared from this view.
Graph of the predicted increase in Earth’s average surface temperature according to a series of climate change scenarios that assume different levels of economic development, population growth, and fossil-fuel use. The assumptions made by each scenario are given at the bottom of the graph.
"global warming." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 2 May 2008 http://www.britannica.com/eb/article-9037044.