Australia’s climate in a Four Degree World - Four Degrees of Global Warming - page 8

158

208

258

308

358

408

458
110E

120E 130E 140E 150E

.

~ ... ------------....................

Likely decrease Uncertain Likely increase

Figure 2.5 Likelihood of increase in annual rainfall across Australia
Note
a As indicated by the fraction of climate model experiments in a multi-model ensemble
showing increase (re-drawn from CSIRO and BoM, 2007).

to decrease and the range is typically around 2 40 to 1 10 per cent. Annual
changes (which factor in rainfall seasonality) can be seen for the selected sites in
Table 2.1 .
The range of change in Perth is from 0 down to 2 50 per cent, Melbourne from
0 down to 2 35 per cent and in Adelaide from 1 5 per cent down to 2 40 per
cent. On the other hand, projected change in Brisbane is from 2 45 to 1 25 per
cent and in Cairns from 2 35 to 1 30 per cent.
In the case of rainfall in Central Victoria ( Figure 2.3b ), the projected changes
(for global warming of around 1 2.8C only, not 1 4°C) are comparable in
magnitude to current decadal variability, and thus may be masked by this varia-
bility for some decades.
These rainfall projections are consistent with the rainfall projections from
the perturbed physics model ensemble ( Figure 2.2 ) , which also show no clear
direction of change in summer rainfall, but a bias to decrease in winter rainfall.
The latter tendency is very strong in the south-west region, where almost none
of the 1,000 simulations considered show an increase in winter rainfall.

In addition to these large ranges of uncertainty in projected rainfall change