Global warming is the rise in temperature of the Earth's atmosphere and oceans. This increase is due to the increasing concentrations of greenhouse gases resulting from deforestation and the burning of fossil fuels.
Global warming has been measured since the late 19th century. NASA Goddard Institute for Space Studies reports that the average surface temperature has increased by about 1.4 F / 0.8 C, with two thirds of this increase occuring since 1980. Climate model projections suggest that the global surface temperature during the 21st century is likely to rise a further 1.1 - 2.9 C (2-5F). The rate of warming is increasing. The United Nations Intergovernmental Panel on Climate Change reports that eleven of the last twelve years were amongst the warmest since 1850. An increase in temperature is causing sea levels to rise and the retreat of glaciers, permafrost and sea ice. The Arctic is feeling the effects the most, with the Arctic ice rapidly disappearing and may have its first ice free summer by 2040. Glaciers and mountain snows are rapidly melting. In the Northern hemisphere the spring thaws are coming a week earlier, and the autumn freezes a week later. Montanas Glacier National Park recorded 150 glaciers in 1950, but this has now reduced to twenty-seven.
The amount and pattern of precipitation is changing, increasing subtropical desert areas. Extreme weather patterns such as heat waves, droughts and heavy rainfall has been attributed to global warming.
Changes in temperature can adversely affect habitats. Many plants and animals live in specific environments and a change of a few degrees in temperature can lead to species extinctions. Coral reefs are particularly sensitive to small changes in water temperature and have suffered die back known as bleaching. In 1998 it was recorded that some areas suffered 70% bleaching. This is expected to increase significantly in the next 50 years as sea temperatures rise.
Many countries have pledged to reduce greenhouse emissions and help slow global warming.