Geoscience Reference
In-Depth Information
feedback effects on climate: for instance, the uplands are too low to generate
significant orographic rainfall, contributing to the aridity of the inland (Orians and
Milewski, 2007). The lack of topographic relief has meant the terrestrial biota has
had few geographic barriers - such as mountain ranges - to limit past dispersal. In
the future, however, this feature will also limit the ability of species to cope with
increasing temperatures by shifting to higher elevation refuges. Consequently,
keeping pace with shifting climate zones will require many terrestrial species to
move overland by many tens or hundreds of kilometres by the end of the century
(Hughes, 2003; Loarie et al., 2009; Leadley et al., 2010b;).
Finally, Australian ecosystems have been modified by human occupation
for at least 40-65,000 years. The use of fire and hunting by Aboriginal peoples
substantially modified the landscape (Bowman, 2003). Far greater impacts,
however, have resulted from European settlement over the past 200 years, with
large areas of the continent cleared or highly modified for agricultural and urban
development (Cocklin and Dibden, 2009). Less than 10 per cent of pre-1750
vegetation remains in the intensive use zones of south-east and south-west
Australia (SoE, 2011) and native vegetation loss continues at nearly one million
ha annually with much of the remaining natural habitat now highly fragmented
(SoE, 2011).
Australia has one of the worst records of species extinctions of any continent.
Nearly 50 per cent of the world's known mammal extinctions have occurred in
Australia in the last 200 years (Johnson, 2006). Over 50 extinctions of plants, birds
and frogs have also been documented (Lindenmayer, 2007). Declines in distribution
and abundance of many other species means they are likely to have little functional
role in ecological communities. The current rate of species extinction (globally
and in Australia) is estimated to be 100-1,000 times higher than background rates
estimated from the fossil record (MEA, 2005). Over 1,700 species and ecological
communities are known to be threatened and at risk of extinction (SoE, 2011)
with the actual number at risk very likely to be considerably higher. Australia's
Biodiversity Conservation Strategy (2010-30) listed: habitat loss, degradation and
fragmentation; invasive species; unsustainable use of natural resources, changes to
aquatic environments and flows; changing fire regimes; and climate change as major
stresses on biodiversity. Climate change represents an additional stress, one that will
add to, and interact with, existing pressures.
Australian landscapes at 4°C
Global meta-analyses of the potential impacts of future warming project large-
scale shifts in biomes (Scholze et al., 2006; Gonzalez et al., 2010) and the
functional collapse of many ecosystems at more than 3-4°C above pre-industrial
levels (e.g. Warren et al., 2011). The main uncertainty is not
whether
such
changes will occur, but their rate and extent (Leadley et al., 2010a).
1
Some ecosystems - such as in the polar regions - are at risk because climate
change will be large in an absolute sense. Others - such as tropical ecosystems
at low latitudes - are vulnerable because the projected change is relatively large
