Williams-Climate-change-refugia-for-terrestrial-biodiversity_0

3.4.5 Distance measures
At a given location, the climate may change dramatically, but if there is large spatial
variation in climates in the vicinity of this location, a population can track its suitable
climate by moving a short distance. On the other hand, if climate is largely
homogenous for large distances around the point of interest, a population needs to
move a long way to track its suitable climate. Thus, a useful measure of climate change
impact is the distance a population would have to move to remain within a suitable
climate space. We estimated this metric for both annual mean temperature and annual
mean precipitation. In the former case, we calculated the distance a population would
have to move by 2085 to stay within 2 SDs of the annual mean temperature at that
location. For annual mean precipitation, given the much smaller relative shifts in this
metric, we used a more stringent criteria; having to stay within 1 SD of local annual
mean precipitation. These measures were calculated for each of the 18 GCMs for four
RCPs (APPENDIX 2. Climate Stability). The 10 th , 50 th and 90 th percentile across the 18
GCMs for RCP 8.5 are detailed in Figure 12.
The results for temperature were compelling, with small required movement distances
surrounding areas of topographic relief (because lowland species can retreat upwards
to these areas as temperature increases). Upland areas at the centre of this
topographic relief, however, typically show very long required movement distances,
because equivalent temperatures in these areas move off the top of mountains and, by
2085 can only be found at far removed locations. This is true for parts of the Great
Dividing Range such as the high elevation areas of the Australian Wet Tropics, the
central Queensland coast uplands, and the New South Wales (NSW) and Victorian
alpine areas. Also, the high elevation areas of the MacDonnell Ranges, Northern and
Central Kimberley, the Pilbara, the Flinders Lofty Block and the Tasmanian Central
Highlands. Interestingly, the low elevation areas of Arnhem Land, the Nullarbor and
south-west Western Australia have no nearby analogous temperatures in 2085. For the
Nullarbor and south-west Western Australia, this is likely to be a consequence of being
situated at the southern edge of the landmass where there are no areas available to
the south that would provide suitable temperatures into the future.
Tellingly, some cells had no corresponding cell within 2 SDs of current temperature; for
these locations there is no place on the continent with equivalent temperatures
in 2085 (APPENDIX 2. Climate Stability). In fact, over 9000 km 2 across the continent
had no corresponding cell within 2 SDs of current predicted by at least one GCM. For
993 km 2 , all 18 GCMs predicted that there would be no area with a similar temperature
by 2085. The areas projected to have no corresponding temperature within 2 SDs are
all high elevations of southern Australia (mostly Victoria and Tasmania). These areas
are currently the coldest parts of Australia, and no area is predicted to be as cold by
2085 (APPENDIX 2. Climate Stability). Many other cells required movements of greater
than 500 km by 2085; distances that are likely impossible for many low vagility taxa.
26 Climate change refugia for terrestrial biodiversity