Global warming is the increase in the average temperature of the Earth's near-surface air and oceans since the mid-twentieth century and its projected continuation. Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) during the 100 years ending in 2005.[1][2] The Intergovernmental Panel on Climate Change (IPCC) concludes that most of the "temperature increase since the mid-twentieth century is very likely[note 1] due to the observed increase in anthropogenic greenhouse gas concentrations",[2][1] and natural phenomena such as solar variation and volcanoes probably[note 2] had a small warming effect from pre-industrial times to 1950 and a small cooling effect from 1950 onward.[3][4] These basic conclusions have been endorsed by 30 scientific societies and academies of science,[5] including all of the national academies of science of the major industrialized countries.[6][7][8]
Climate model projections summarized in the latest IPCC report indicate that global surface temperature will likely rise a further 1.1 to 6.4 °C (2.0 to 11.5 °F) during the twenty-first century.[1] Increasing global temperature will cause sea levels to rise and will change the amount and pattern of precipitation, likely including an expanse of the subtropical desert regions.[9] Other likely effects include Arctic shrinkage and resulting Arctic methane release, shrinkage of the Amazon rainforest, increases in the intensity of extreme weather events, changes in agricultural yields, modifications of trade routes, glacier retreat, species extinctions and changes in the ranges of disease vectors. The IPCC has warned that global warming "could lead to some effects that are abrupt or irreversible".
Political and public debate continues regarding the appropriate response to global warming. The available options are mitigation to reduce further emissions; adaptation to reduce the damage caused by warming; and, more speculatively, geoengineering to reverse global warming. Most national governments have signed and ratified the Kyoto Protocol aimed at reducing greenhouse gas emissions.
Notes
edit- ^ In this Summary for Policymakers, the following terms have been used to indicate the assessed likelihood, using expert judgement, of an outcome or a result: Virtually certain > 99% probability of occurrence, Extremely likely > 95%, Very likely > 90%, Likely > 66%, More likely than not > 50%, Unlikely < 33%, Very unlikely < 10%, Extremely unlikely < 5%[1]
- ^ Because solar variability before the satellite period must be scaled from proxy data, large uncertainty exists about phase and magnitude of the forcing. Without anthropogenic forcing, the 20th century warming is small. The simulations with only natural forcing components included yield an early 20th century peak warming of ≈0.2 °C (≈1950 AD), which is reduced to about half by the end of the century because of increased volcanism.[4]
References
edit- ^ a b c "Summary for Policymakers" (PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change. 2007-02-05. Retrieved 2007-02-02.
{{cite web}}: Check date values in:|date=(help) - ^ a b Global surface temperature is defined in the IPCC Fourth Assessment Report as the average of near-surface air temperature over land and sea surface temperature.
- ^ Hegerl, Gabriele C. (2007-05-07). "Understanding and Attributing Climate Change" (PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change. p. 690. Retrieved 2007-05-20.
Recent estimates (Figure 9.9) indicate a relatively small combined effect of natural forcings on the global mean temperature evolution of the seconds half of the twentieth century, with a small net cooling from the combined effects of solar and volcanic forcings
{{cite web}}: Check date values in:|date=(help); Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Ammann, C. M.; Joos, F.; Schimel, D. S.; Otto-Bliesner, B. L.; Tomas, R. A. (2007-04-06). "Solar influence on climate during the past millennium: Results from transient simulations with the NCAR Climate Simulation Model" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 104 (10): 3713–3718. doi:10.1073/pnas.0605064103. PMC 1810336. PMID 17360418.
However, because of a lack of interactive ozone, the model cannot fully simulate features discussed in (44)." "While the NH temperatures of the high-scaled experiment are often colder than the lower bound from proxy data, the modeled decadal-scale NH surface temperature for the medium-scaled case falls within the uncertainty range of the available temperature reconstructions. The medium-scaled simulation also broadly reproduces the main features seen in the proxy records." "Without anthropogenic forcing, the 20th century warming is small. The simulations with only natural forcing components included yield an early 20th century peak warming of ≈0.2 °C (≈1950 AD), which is reduced to about half by the end of the century because of increased volcanism.
{{cite journal}}: Check date values in:|date=(help) - ^ The 2001 joint statement was signed by the scientific academies of Australia, Belgium, Brazil, Canada, the Caribbean, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden, and the UK. The 2005 statement added Japan, Russia, and the U.S. The 2007 statement added Mexico and South Africa. Professional societies include American Meteorological Society, American Geophysical Union, American Institute of Physics, American Astronomical Society, American Association for the Advancement of Science, Stratigraphy Commission of the Geological Society of London, Geological Society of America, American Chemical Society, and Engineers Australia.
- ^ "The Science Of Climate Change". Royal Society. May 2001. Retrieved 2008-01-04.
{{cite web}}: CS1 maint: date and year (link) - ^ "Joint science academies' statement: Global response to climate change". Royal Society. June 2005. Retrieved 2008-01-04.
{{cite web}}: CS1 maint: date and year (link) - ^ "Joint science academies' statement on growth and responsibility: sustainability, energy efficiency and climate protection" (PDF). Potsdam Institute for Climate Impact Research. May 2007. Retrieved 2008-01-04.
{{cite web}}: External link in|publisher= - ^ Lu, Jian; Vecchi, Gabriel A.; Reichler, Thomas (2007). "Expansion of the Hadley cell under global warming" (PDF). Geophysical Research Letters. 34 (6): L06805. doi:10.1029/2006GL028443. Retrieved 2008-12-06.