Current warming and likely future impacts - Climate Change: Biological and Human Aspects - page 325

are covered with grass and, indeed, trees (Thomas et al., 2005). This is an important
biome because desert dunes, whether dry and active, such as in much of the Sahara
Desert, or inactive, covered by vegetation north of the Kalahari Desert, account for
5% of the global land surface and 30% in Africa. Knowing how moisture levels
determined by precipitation and plant evapotranspiration, together with wind speeds,
combine to affect dune mobility, they were able to apply climate models to see
the effect on sand dunes. If, due to global warming and regional climate change,
temperatures rise without a counteracting increase in rainfall, and factoring in wind
speeds, then vegetation that currently stabilises dunes could die, and the dunes could
mobilise. This would also kill off other vegetation previously sheltered by the dune,
and so the sandy desert would return. Such an analysis suggests that the current
situation is precarious. It would appear that regardless of which IPCC future scenario
is considered, the southern dunes bordering the dry Kalahari Desert that are already
mobile will become prone to greater movement by 2040. Meanwhile, the eastern and
northern dune fields that are currently covered by trees and/or grass could become
mobile by 2070. By 2100 all dune fields from northern South Africa to Angola and
Zambia may become mobile. The authors conclude, 'There are uncertainties within
the modelled Kalahari scenarios but the general trend and the magnitude of possible
change in the erodibility and erosivity of dune systems suggests that the environmental
and social consequences of these changes will be drastic' (Thomas et al., 2005).
In 2011 a large international team of researchers, led by Michael Burrows, David
Schoeman and Lauren Buckley, published research in the journal Science that mapped
the distances that species range would have to move based on actual climate change
in the past half century. They used two measures of thermal shifts that species
would have to (try to) track: the velocity of climate change as in the geographical
movements of isotherms (temperature), and the phenological shift (seasonal timing)
of temperatures. These indices resulted in a complex mosaic of predicted range shifts
and phenology changes that deviated from a straightforward poleward migration that
a simple analysis based on the global temperature and average latitude temperatures
would have given.
Be it vegetation changes in sand dunes, species range migration or many of the
other responses to climate change discussed in this chapter, the likelihood with
confounding factors is that change will not be smooth but at some point will move
rapidly to a new state. Such points are critical in the transition and thresholds to new
environmental, climatic and or ecological conditions. We will return to this later this
chapter.
6.5 Biologicalresponsestogreenhousetrendsbeyondthe
21stcentury
Biome shifts and ecosystem change, with their consequential impacts on human
activities, have been a theme of this chapter. As we shall see when looking at the
human ecology of anthropogenic global warming, it is most likely (some other global
catastrophe aside) that fossil fuel burning will continue throughout this century, so