Lawrence says: Global warming is the increase in the average temperature of Earth's near-surface air and oceans since the mid-20th century and its projected continuation.
Global surface temperature increased 0.74 ± 0.18 °C (1.33 ± 0.32 °F) between the start and the end of the 20th century. The Intergovernmental Panel on Climate Change (IPCC) concludes that most of the observed temperature increase since the middle of the 20th century was very likely caused by increasing concentrations of greenhouse gases resulting from human activity such as fossil fuel burning and deforestation.
The IPCC also concludes that variations in natural phenomena such as solar radiation and volcanic eruptions had a small cooling effect after 1950.
These basic conclusions have been endorsed by more than 40 scientific societies and academies of science, including all of the national academies of science of the major industrialized countries.
It is usually impossible to connect specific weather events to global warming. Instead, global warming is expected to cause changes in the overall distribution and intensity of events, such as changes to the frequency and intensity of heavy precipitation.
Broader effects are expected to include glacial retreat, Arctic shrinkage including long-term shrinkage of the Greenland ice sheet, and worldwide sea level rise. Some effects on both the natural environment and human life are, at least in part, already being attributed to global warming.
A 2001 report by the IPCC suggests that glacier retreat, ice shelf disruption such as that of the Larsen Ice Shelf, sea level rise, changes in rainfall patterns, and increased intensity and frequency of extreme weather events are attributable in part to global warming. Other expected effects include water scarcity in some regions and increased precipitation in others, and changes in mountain snowpack.
Social and economic effects of global warming may be exacerbated by growing population densities in affected areas. It is expected that the health benefits of climate change (e.g., fewer deaths from cold exposure) will be outweighed by negative health effects (e.g., increased levels of malnutrition), especially in developing countries.
A summary of probable effects and recent understanding can be found in the IPCC Fourth Assessment Report.
According to this report, there is observational evidence for an increase in intense tropical cyclone activity in the North Atlantic Ocean since about 1970, in correlation with the increase in sea surface temperature (see Atlantic Multidecadal Oscillation), but that the detection of long-term trends is complicated by the quality of records prior to routine satellite observations.
The summary also states that there is no clear trend in the annual worldwide number of tropical cyclones.
Alberto blurted out: Holography is a technique which enables three-dimensional images (holograms) to be made.
