1996 and 1997 were the warmest years on average around the world since 1860.
Scientists believe temp will increase two-degree in the next 100 years–will cause a sea level rise of approx. 50cms.
Some climatologists believe the rate of warming within the atmosphere is greater know than in those periods of wanning after earlier ice ages. Some believe temp changes are within the range of natural temperature swings.
All agree that warming is due to an increase in the enhanced greenhouse effect resulting from an increase in the emissions of greenhouse gases.
United Nations intergovenm1ental panel on climatic change in 1994 noted that the rate of global warming had increased between 10 and 30 % over the previous two years. At the same time carbon dioxide emissions had also increased during that period after an interval of stability in the growth of emissions.
Reasonable agreement that there has been heating of the atmosphere by about .5–.7 degrees.
Significance of Global Warming for the World
Northern Europe to warm up
Tropics to increase at the expense of the polar regions
Coral reefs to die- unable to cope with sudden sea level rise
Forests sensitive to high temp will disappear
Food production will decrease in areas unpredictable weather
Small islands will be swamped
Low lying delta regions will be flooded more often
Shortage of water as warmer weather dries out rivers and streams
Heat stress mortality and vector borne disease will increase
Extreme storms and unpredictable events will cause flooding and damage
El Nino and Enso will be more frequent
Significance to Australia
20% more summer rainfall in northern and eastern areas.
10- 20% less winter rainfall in southern and southwestern areas.
Rainfall may increase in central and western Australia
Cyclone belt will move south
Monsoon will become more intense
Loss of land and amenities in coastal locations due to sea level rise
Temperature increase of 2-3 degrees in coastal eastern Australia
Inland Australia temp increase of 4-5 degrees
Brisbane – warmer, wetter and less windy
Sydney – like Brisbane
Melbourne – drier, warmer and windier.
Adelaide and Perth could be drier, warmer and less windy
Darwin – warmer, wetter and less windy
40% more vegetation on some desert areas in northern Australia
Wheat growing areas–higher rainfall will shift the planting into poorer more marginal soil
Inland Queensland–cropping to replace grazing in areas of increased rainfall
The Variability and Effectiveness of Rainfall
Rainfall generally decreases inland and therefore the effectiveness of this rainfall for various forms of land-use changes from cropping and intensive livestock activities closer to the coast to no cropping and extensive livestock activities in the drier inland.
The principal control on the distribution and intensity of land use is the availability of soil moisture.
Effective rainfall means the average number of months where the average precipitation is greater than evapotranspiration.
The main cereal producing regions are in areas with 5-9 months of effective moisture, Higher rainfall zones land use is more intensive, with fat lamb and cattle production on well-watered pastures being the norm.
Intensive cropping is possible where there is 9 months of effective rainfall. This area is very limited in extent and much of the land is too mountainous for cultivation.
Environmental factors that influence the effectiveness of rainfall and viability of land use are; soil productivity- fertilizers, trace elements deficiencies and salinity. Topography – steep land, Drainage- low lying, water logged soils.
The definition of drought varies depending upon the activities carried out in a particular location.
Drought is commonly defined as a long period without rainfall, in a climate regime where evapotranspiration exceeds precipitation and water levels in the soil are lowered.
The physical causes of drought have their origins in the natural fluctuations of the global climate system.
1994/95 drought conditions: A persistent belt of high pressure lodged itself over a very wide area of Australia. Normally their would be a procession of high and low pressure systems, with cold fronts bringing the possibility of rainfall, however the high pressure system blocked their passage for months on end. The failure of expected rains left wide areas without sufficient water supplies.