The results may also be used to examine the interaction between adaptation and
mitigation. Adamson, Mallawaarachchi, and Quiggin (2009) show that the state-
contingent modelling framework yields simple first-order approximations for the
impact of climate change in the absence of adaptation.
The impact of an equiproportional reduction in the availability of water in all
states of nature may be approximated on the assumption that the allocation of
land to all irrigated agriculture activities is reduced in the same proportion, with
the land so released being converted to dryland production. The impact of a
change in the probability distribution of states of nature may be modelled by
holding state-contingent returns constant and calculating the change in expected
return associated with the given change in probabilities.
In Table 4, we report the results of estimates of the impact of climate change on
the value of water used in irrigation, in the absence of adaptation, and compare
these to the simulated values reported in Table 2. The difference, reported in the
final column of Table 4, is an estimate of the benefits of adaptation. Adaptation
is beneficial in every case. For the simulations presented here, adaptation and
mitigation are complements. That is, the benefits of adaptation are higher in the
simulations with mitigation than in the ‘adaptation only’ simulation.
The complementarity relationship between mitigation and adaptation reflects
several features of the projections and simulations considered here. First, in the
absence of mitigation, the supply of water is so limited by 2100 that there is little
scope for adaptation. This point is true for a wide range of ecological and
agricultural systems affected by climate change. Adaptation is a useful response
to moderate rates of climate change. However, where climate change produces a
rapid and radical change in conditions, adaptation of existing ecosystems and
human activities may not be feasible. Instead, the systems in question will
undergo collapse. New systems will ultimately emerge, but stable adaptation
may not be feasible until the climate itself has stabilized at a new equilibrium.
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