Global Heat Wave (Borrowed from Miss Roche’s Site)
Global Heat Wave
Global warming is an increase in the average temperature of the Earth’s near-surface air and oceans. Although global warming has occurred in the past, the term is most often used to refer to the warming some scientists predict will occur as a result of increased emissions of greenhouse gases.
Global average air temperature near Earth’s surface rose 0.74 ± 0.18 °Celsius (1.3 ± 0.32 °Fahrenheit) in the last century. The Intergovernmental Panel on Climate Change (IPCC) concludes, “most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations,” which leads to warming of the surface and lower atmosphere by increasing the greenhouse effect. Other phenomena such as solar variation and volcanoes have had a small neutral or slight cooling effect on global mean temperature since 1950. While this conclusion has been endorsed by numerous scientific societies and academies of science, there are a few scientists who disagree about the primary causes of the observed warming.
Models referenced by the IPCC predict that global temperatures are likely to increase by 1.1 to 6.4 °C (2.0 to 11.5 °F) between 1990 and 2100. The range of values reflects the use of differing scenarios of future greenhouse gas emissions as well as uncertainties regarding climate sensitivity. Although most studies focus on the period up to 2100, warming and sea level rise are expected to continue for more than a millennium even if no further greenhouse gases are released after this date. This reflects the long average atmospheric lifetime of carbon dioxide (CO2).
An increase in global temperatures can in turn cause other changes, including a rising sea level and changes in the amount and pattern of precipitation. There may also be increases in the frequency and intensity of extreme weather events, though it is difficult to connect specific events to global warming. Other consequences include changes in agricultural yields, glacier retreat, reduced summer streamflows, species extinctions and increases in the ranges of disease vectors.
Remaining scientific uncertainties include the exact degree of climate change expected in the future, and especially how changes will vary from region to region across the globe. A hotly contested political and public debate also has yet to be resolved, regarding whether anything should be done, and what could be cost-effectively done to reduce or reverse future warming, or to deal with the expected consequences. Most national governments have signed and ratified the Kyoto Protocol aimed at combating greenhouse gas emissions.