Climate change, mitigation and adaptation: the case of the Murray–Darling Basin in Australia

to ‘business as usual’ to describe projections in which carbon emissions are not
constrained by mitigation policies.

As shown by Quiggin and Horowitz (2003), the main costs of climate change for
agricultural producers are costs of adaptation and adjustment. It follows that the
rate of change of warming is at least as important as the equilibrium change in
temperature levels. Recent observed warming has been at a rate of around 0.2
degrees per decade (Hansen et al. 2006). ‘Adaptation only’ projections imply an
increase in the rate of warming over coming decades.

Water

Water, derived from natural precipitation, from irrigation or from groundwater,
is a crucial input to agricultural production. IPCC (2007b, Chapter 3, p. 175)
concludes, with high confidence, that the negative effects of climate change on
freshwater systems outweigh its benefits. In addition to raising average global
temperatures, climate change will affect the global water cycle. Globally, mean
precipitation (rainfall and snowfall) is projected to increase due to climate
change. However, this change will not be uniform.

Climate change is projected to increase the variability of precipitation over both
space and time. Areas that are already wet are likely to become wetter, while
those that are already dry will in many cases become drier, with average
precipitation increasing in high rainfall areas such as the wet tropics, and
decreasing in most arid and semi-arid areas (Milly, Dunne and Vecchia 2005).
Where precipitation increases there are likely to be more frequent events
involving very high rainfall, such as monsoon rain associated with tropical
cyclones (IPCC 2007a).

Severe droughts are also likely to increase by multiples ranging from two to ten,
depending on the measure (Burke, Brown, and Nikolaos 2006) particularly in
the temperate zone between 30 and 60 degrees latitude.

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