MORE INFORMATION- CLIMATE CHANGE

Modelling of Climate Change at the National Level

In Australia, similar climate modelling work has been carried out by the ‘Australian Climate Change Science Program’ a cooperative venture between scientists from the Bureau of Meteorology, the CSIRO, and the other commonwealth government institutions concerned about the impacts of climate change on the Australian environment. Their report in 2007 entitled “Climate Change in Australia” concluded that, relative to the climate of 1990,

‘the best estimate of annual warming over Australia by 2030 is around 1.0 oC, with warmings of around 0.7-0.9 oC in coastal areas and 1-1.2 oC inland. Mean warming in winter is a little less than in the other seasons, as low as 0.5 oC in the far south …’

and

‘Later in the century, the warming is more dependent upon the assumed emission scenario.’

According to the ‘Australian Climate Change Science Program’ report, by 2050 a temperature rise of 1.20C in the Australian mean temperature above the 1990 temperature could be expected for a low emission scenario, but if greenhouse gas emissions failed to be controlled, the temperature rise could be 2.20C. By 2070 the rise could be 1.80C for (a low emission scenario) or 3.40C for a high emission scenario. These are best estimates but there is a large margin for error in these model projections.

Analysis of past trends in precipitation in Australia and the attempt to model future effects of global warming on precipitation is complicated by the fact that Australian rainfall is characterised by large year to year variability partly in association with the El Nino – Southern Oscillation (ENSO).  This reduces the reliability of conclusions about precipitation compared with those about temperature. Nevertheless, the ‘Australian Climate Change Science Program’ reports:

‘Similar to temperature trends, rainfall trends show a marked contrast between the first half of the last century and the period since 1950.  …  North-west Australia has seen an increase in annual rainfall over this period amounting to more than 30 mm per decade across the north-west third of Australia and exceeding 50 mm per decade on parts of the north-west coast. In marked contrast, eastern and south-western Australia have become drier since 1950, with largest drying along the east coast exceeding 50 mm per decade. … In the south-west of Western Australia the rainfall decline reflects an apparent step-change to lower rainfall in the 1970s, exacerbated by very low rainfall in recent years.’  

and

‘The rainfall decreases in south western Australia since the mid-1970s is likely to be at least partly due to anthropogenic increase in greenhouse gases. It is not-yet possible to attribute the post-1950 rainfall decreases in eastern Australia and rainfall increases in north-western Australia to human activities. Droughts have been accompanied by higher surface temperatures due to anthropogenic warming. This may have exacerbated the impact of drought in regions where warming increases water demand and surface water loss.’ 

As to the future, the modelling work of the Australian Climate Change Science Program envisages that future precipitation patterns in Australia are likely to change in response to the global warming. Figure 6, below, illustrates graphically the trend over the coming century for the climate model’s ‘best estimate’ of precipitation in the case of a medium level greenhouse gas emission scenario. It should, however, be noted that there is a much higher amount of uncertainty in these model projections for precipitation than there is for model projections of temperature.

Up to 2030 it is projected that there will be ‘little change’ in the annual precipitation of the far north of Australia but ‘decreases of 2% to 5% elsewhere’. South Western Australia is the region that is expected to be worst affected by reduced rainfall.

Later on in the century, precipitation is projected to be much more affected by the particular global greenhouse gas emissionscenario that unfolds. If global emissions can be controlled at low levels, the ‘best estimate’ is that there will be ‘little change’ in the rainfall in the far north ‘grading southwards to a decrease of 5%’. On the other hand, if global emissions turn out to be high then the best estimate is that rainfall in the south could decrease by 7.5% and be more seasonally and regionally variable.


    
Figure 6:  Amount of rainfall predicted in the case of a medium level emission scenario for the years 2030 and 210 expressed as a % change relative to the actual 1980-1999 rainfall average. (Source: CSIRO Mark 3.5 climate model in Climate Change in Australia - to view an animated version of the climate modelling predictions regarding rainfall in Australia see: http://www.climatechangeinaustralia.gov.au/documents/resources/rainfall.avi [Accessed October 2008])

Other climate change projections for the Australian environment based on the CSIRO/Bureau of Meteorology modelling include:

  • ‘Annual potential evapotranspiration is projected to increase over Australia. Largest increases are in the north and east, where the change by 2030 ranges from little change to a 6% increase, with best estimate of around a 2% increase’
  • ‘Drought occurrence is projected to increase over most of Australia, but particularly in south-western Australia’
  • ‘There is a tendency for increased wind speed in most coastal areas in 2030 … Later in the century, changes of wind strength can be larger, depending on the emission scenario.’
  • ‘A substantial increase in fire weather risk is likely at most sites in southeastern Australia.’
  • ‘Global sea level rise is projected by the IPCC to be 18-59 cm by 2100, with a possible additional contribution from ice sheets of 10 to 20 cm. However, further ice sheet contributions … may substantially increase the upper limit of sea level rise.’
  • ‘Storm surges occurring in conditions of higher mean sea levels will enable inundation and damaging waves to penetrate further inland, increasing flooding, erosion and the subsequent impacts on built infrastructure and natural ecosystems.’
  • ‘Increases in ocean acidity are expected in the Australian region with the largest increases in the high- to mid-latitudes … affecting the capacity for shell and endoskeleton creation by marine organisms.’
  • ‘Similar to studies for other basins, Australian regional studies indicate a likely increase in the proportion of the tropical cyclones in the more intense categories, but a possible decrease in the total number of cyclones.’
    (Source: “Climate Change in Australia” CSIRO and BOM 2007,   pp. 10-12)