| Global warming is the increase in the average | | | | levels are stabilized. This reflects the |
| temperature of the Earth's near-surface air | | | | large heat capacity of the oceans. |
| and oceans in recent decades and its | | | | |
| projected continuation. | | | | An increase in global temperatures can in |
| | | | turn cause other changes, including sea level |
| Global average air temperature near the | | | | rise, and changes in the amount and pattern |
| Earth's surface rose 0.74 ± 0.18 °C | | | | of precipitation. There may also be changes |
| (1.3 ± 0.32 °F) during the past | | | | in the frequency and intensity of extreme |
| century. The Intergovernmental Panel on | | | | weather events, though it is difficult to |
| Climate Change (IPCC) concludes, "most of the | | | | connect specific events to global warming. |
| observed increase in globally averaged | | | | Other effects may include changes in |
| temperatures since the mid-20th century is | | | | agricultural yields, glacier retreat, reduced |
| very likely due to the observed increase in | | | | summer streamflows, species extinctions and |
| anthropogenic greenhouse gas concentrations," | | | | increases in the ranges of disease vectors. |
| which leads to warming of the surface and | | | | |
| lower atmosphere by increasing the greenhouse | | | | Remaining scientific uncertainties include |
| effect. Natural phenomena such as solar | | | | the exact degree of climate change expected |
| variation combined with volcanoes have | | | | in the future, and how changes will vary from |
| probably had a small warming effect from | | | | region to region around the globe. There is |
| pre-industrial times to 1950, but a cooling | | | | ongoing political and public debate regarding |
| effect since 1950. The basic conclusions have | | | | what, if any, action should be taken to |
| been endorsed by at least 30 scientific | | | | reduce or reverse future warming or to adapt |
| societies and academies of science, including | | | | to its expected consequences. Most national |
| all of the national academies of science of | | | | governments have signed and ratified the |
| the major industrialized countries. The | | | | Kyoto Protocol aimed at combating greenhouse |
| American Association of Petroleum Geologists | | | | gas emissions. |
| is the only scientific society that rejects | | | | |
| these conclusions, and a few individual | | | | Terminology |
| scientists also disagree with parts of them. | | | | |
| | | | The term "global warming" is a specific |
| Climate models referenced by the IPCC project | | | | example of the broader term climate change, |
| that global surface temperatures are likely | | | | which can also refer to global cooling. In |
| to increase by 1.1 to 6.4 °C (2.0 to 11.5 | | | | common usage the term refers to recent |
| °F) between 1990 and 2100. The range of | | | | warming and implies a human influence. The |
| values reflects the use of differing | | | | United Nations Framework Convention on |
| scenarios of future greenhouse gas emissions | | | | Climate Change (UNFCCC) uses the term |
| and results of models with differences in | | | | "climate change" for human-caused change, and |
| climate sensitivity. Although most studies | | | | "climate variability" for other changes. The |
| focus on the period up to 2100, warming and | | | | term "anthropogenic climate change" is |
| sea level rise are expected to continue for | | | | sometimes used when focusing on human-induced |
| more than a millennium even if greenhouse gas | | | | changes. |