Geoscience Reference
In-Depth Information
more difficult to determine because fire behaviour depends also on fuel type and
accumulation, which may change in the future due to changes in rainfall, fire
frequency and other factors (Williams et al., 2009).
Tropical cyclones
For the Australian region, the CCAM model has produced downscaled climate
simulations on a 65km grid for a high (A2) emissions scenario for a period
centred on 2070, when the global warming is 1.35-3.60°C (CSIRO and BoM,
2007). The CCAM projections show a strong tendency for a decrease in the
frequency of cyclones in the Australian region (Abbs, 2010). On average, for the
period 2051-90 relative to 1971-2000, the simulations show an approximately
50 per cent decrease in frequency, a small decrease (0.3 days) in the duration of
a given cyclone and a southward movement of 100km in the genesis and decay
(the region into which weakened tropical cyclones migrate) is greater off the
Queensland coast than off the coast of Western Australia.
The Regional Atmospheric Modelling System (RAMS) was used to further
downscale to a grid-spacing of 15km for 40-year time slices centred on 1980,
2030 and 2070 (Abbs, 2010). For each time slice, 100 cyclone events were
modelled. These simulations show a distinct shift towards stronger cyclones, with
a larger percentage of cyclones producing high wind speeds (exceeding 25 m/s)
in the 2070 climate.
Extreme sea levels
IPCC (2007) estimates of future sea level rise are 18-79cm by 2090-2099 relative
to 1980-1999, based on climate modelling and allowing an extra 10 to 20cm for
a possible rapid dynamic response of the Greenland and West Antarctic ice
sheets (Meehl et al., 2007). Higher estimates have been suggested using statis-
tical methods that relate sea level changes to temperature changes, but there has
been debate about the validity of these approaches (Lowe and Gregory, 2010).
As stated above, extreme sea level events can be due to high tides, local storm
surges due to low pressure systems such as cyclones, distant storms that generate
high waves, and a rise in average sea level. Projected changes in extreme sea level
events around southern Australia are likely to be dominated by the average sea
level rise, rather than changes in storm surges (Colberg and McInnes, 2012). For
the high (A2) emission scenario, the range of mean sea-level rise by 2090-2100
is 23-51cm, which corresponds to a global warming of 2.0-5.4°C.
Figure 3.11
shows the estimated increase in the frequency of extreme sea-level
events caused by a 50cm mean sea-level rise for 29 Australian locations where
good tidal records longer than 30 years exist (DCC, 2009). Extreme events that
now happen every 10 years, on average, would happen about every 10 days in
2100, and become even more frequent around Sydney, with smaller increases
around Adelaide and along parts of the Western Australian coast (DCC, 2009).
