Climate Change & Global Warming
Within the period following the Industrial Revolution, the global temperature has increased. Global surface temperatures have increased about 0.6°C (1.1°F +/- 0.5°F) over the 20th century, and about 0.2 to 0.3°C (0.5° F) over the past 25 years. The recent warming has been greatest over North America and Eurasia between 40 and 70°N. Glaciers and ice caps have been receding for the last 100 years. Precipitation has increased in high latitudes of the northern hemisphere, and decrease in the tropics and subtropics from Africa to Indonesia. Many scientists relate this to human activity modifying the Earth's atmosphere sufficiently to influence global weather and climate patterns. Specifically there is a correspondence between increasing concentrations of greenhouse gases and the rate of increasing global temperature. A number of other anecdotal servations support the contention of global warming.
The clearest signal of global warming in the oceans is a general warming of the upper ocean. The global averaged sea surface temperature (SST) has increased by about 0.6°C (about 1.0°F) since the late 19th century, and about 0.3°C (0.5°F) in the past 25 years. Some areas have displayed greater warming; some less warming and even cooling due to the transport of heat by changing ocean currents. The deep ocean has shown signs of a general warming as well. Global sea level has risen 10-25 cm (7 in. +/-3 in.) during the 20th century. The melting of glaciers and ice caps adds water to the oceans. Water also expands as it warms, raising sea level. Other factors, such as changes in the ice sheet volumes in Greenland and Antarctica, extraction of groundwater for agriculture, and changes in the volume of lakes and seas, account for less than half the observed increase in sea level in the 20th century.