Despite the strong conclusions of the international and Australian scientific communities there are people yet to be convinced that human-induced climate change is likely to or already having adverse impacts.
Climate scientists tend to focus on what might happen decades into the future based on scenarios of varying greenhouse gas emissions. However, the starting point should be the pre-industrial climate or at least the reliable climatic data of the 20th century. Observed trends of rising temperatures, more severe droughts, depleted water resources, more heatwaves, shifting storm tracks, rising sea levels and other more extreme events provide a good basis for looking at costs to date.
While it is natural to attribute increasingly severe weather-related events to human-induced climate change, science cannot be 100 per cent certain with regard to any particular individual event. Rigorous science deals in changing probabilities and risk. The science community says the chances are high that increasing greenhouse gas concentrations are at least partly to blame for more extreme conditions.
We can therefore weigh up the costs already being incurred which are likely due at least in part to climate change experienced to date as well as to increasing exposure in increasingly unsafe areas.
The present drought in south-eastern Australia has been ongoing since at least 2001.
In September 2007, the total surface water stored in the Murray Darling Basin was only some 2 cubic km, or about 23 per cent of capacity. Cumulative loss of groundwater has been about ten times as much. Even average to above-average rainfall will not restore the situation to non-drought conditions for many years.
This ongoing drought has resulted in low or zero irrigation allocations, leading to serious impacts on irrigation farmers and their communities, including local unemployment and some loss of rural populations. Losses of biodiversity have occurred with the death of river red gums and the drying of wetlands, and dire consequences for the lakes at the Murray mouth including the Coorong.
According to scientists in the joint CSIRO and Bureau of Meteorology Centre for Australian Weather and Climate Research (CAWCR) human-induced climate change is likely to be a major cause of this “drought”. This is due to two factors: decreasing rainfall associated with increasing atmospheric pressure in the region, with the rainfall belt moving further south, and increasing evaporative losses from plants and remaining wet surfaces.
Attribution of this long-term “drought” to human-induced climate change is greatly strengthened by global climate model results that indicate that for a greenhouse-warmed world the rainfall belts in both hemispheres will move poleward. Drying is thus predicted to occur in “Mediterranean-type” climates (climate with winter rainfall maxima) in southern Europe, California, southern Africa and Australia, as has been observed.
As average temperatures rise due to global warming so too does the frequency of extreme high temperatures.
A major heat wave in 2003 is well documented for Europe. There were an estimated 35,000 additional deaths. In 2008 Adelaide experienced a heat wave with 15 days over 35˚C, estimated to have a frequency of 1 in 3000 years based on the past record.
The southeast Australian heatwave of late January 2009 caused an estimated 374 excess deaths in Victoria according to the Victorian Department of Human Services, more than twice the 173 deaths in the bushfires of “Black Saturday”, February 7, and damaged crops. Adaptive measures could reduce some of the damage or deaths from heat waves.
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