Global climate change has emerged as a long term environmental challenge of global significance. The Inter-governmental Panel on Climate Change (IPPC), established under the auspices of the United Nations, notes a high probability of continuing global climatic change if Greenhouse Gases (G.H.G) emissions continue to increase (IPCC, 2001). Based on current levels of GHG in the atmosphere, even immediate reductions in emissions will not be rapid enough to reverse the observed changes in climate in the short term (Burton and Van Aalst; 1999).
For the purpose of explanation, the general parameters of climate as perceived on global scale can be expressed in a hierarchy of primary, secondary and tertiary parameters.
1. Temperature extreme (Cold and Heat)
Mean temperature are increasing around the world, and the frequency and intensity of heat waves also appear to be on the increase (Dell-Marta et al, 2007). Climate models predict increased frequency and intensity of heat waves for the future as well (Meehl and Tebaldi, 2004; IPCC, 2007). This poses direct threat to health through heat stress, especially for the elderly, young, children and those with pre-existing health problems. Heat waves exacerbated in the urban environments by the urban heat-island effects, caused by the concentration of concrete and asphalt surface, reduction of vegetation and anthropogenic heat sources. Urban temperatures can be as much as 8oc higher than the surrounding countryside, though typically the increase is more in the order of 3-4oc (Oke, 1997).
2. Wind, Storms and Floods
Climate change is likely to bring increases in the frequency and intensity of heavy precipitation events and in the intensity of tropical cyclonic storms with larger peak wind speeds and heavier precipitation due to warmer sea surface temperatures. The frequency of tropical cyclonic storms is projected to stay constant or decline, although the IPCC is not confident in this conclusion, noting, the apparent increase in the proportion of very intense storm since 1970 in some regions is much larger than simulated by current models for that period ( IPCC, 2007 summary for policy makers)
Climate change may be altering patterns of hydro climatic (moisture) variability during the 20thCentury [Example Karl and Knight, 1998]. It is important to consider the longer term nature of moisture variation. Land based precipitation measurements have been have been amalgamated in gridded data sets (Hulme, 1992; Dai et al, 1997; Hulme et al, 1998) and extended to drought indices.
4. Precipitation, Storm and Drought
The intensity of tropical cyclones (hurricanes) in the North Atlantic has increased over the past 30years which correlates with increases in tropical sea surface temperatures. Storms with heavy precipitation have increased in frequency over most land areas. Between 1900 and 2005, long-term trends shows significantly increased precipitation in eastern parts of Northern and Southern America, North Europe and Northern and Central Asia. Between 1900 and 2005, the Sahel (boundary between the Sahara desert and more fertile regions Africa to the south), the Mediterranean, Southern Africa and parts of Southern Asia have become drier, adding stress to water resources in the tropics and subtropics.
5. Ice sheet and Thawing
Since 1900, the Northern hemisphere has lost 7% of the maximum area covered by seasonally frozen ground and Mountain glaciers have declined worldwide. Since 1978, Satellite data show that the extent of Arctic sea ice during the summer has shrunken by more than 20%.
6. Rising sea levels
Since 1961, the worlds oceans have been absorbing more than 80% of the heat added to the climate, causing ocean water to expand and contributing to rising sea levels. Between 1993 and 2003 ocean expansion was the largest contributor to sea level rise, melting glaciers and losses from the Greenland and Antarctic ice sheets have also contributed to recent sea level rise.