168 The impactsof climate change
Modelling the impact of climate change on world
food supply
An example illustrating the key elements of a detailed study of the impact
of climate change on world food supply is shown in Figure 7.10.^41
A climate change scenario is first set up with a climate model of
the kind described in Chapter 5. Models of different crops that include
the effects of temperature, precipitation and CO 2 are applied to 124
different locations in 18 countriesto produce projected crop yieldsthat
can be compared with projected yields in the absence of climate change.
Included also are farm-level adaptations, e.g. planting date shifts, more
climatically adapted varieties, irrigation and fertiliser application. These
estimates of yield are then aggregated to provide yield-change estimates
by crop and country or region.
These yield changes are then employed as inputs to a world food
trade model that includes assumptions about global parameters such
as population growth and economic change and links together national
and regional economic models for the agricultural sector through trade,
world market prices and financial flows. The world food trade model
can explore the effects of adjustments such as increased agricultural in-
vestment, reallocationof agricultural resourcesaccording to economic
returns (including crop switching) and reclamation of additional arable
land as a response to higher cereal prices. The outputs from the total pro-
cess provide information projected up to the 2080s on food production,
food prices and the number of people at risk of hunger (defined as the
populationwith an income insufficient either to produce or to procure
their food requirements).
The main results with this model for the 2080s regarding the impact
of climate change following the IS 92a scenario (Figure 6.1) are that
yields at mid to high latitudes are expected to increase, and at low lati-
tudes (especially the arid and sub-humid tropics) to decrease. This pattern
becomes more pronounced as time progresses. The African continent is
particularly likely to experience marked reductions in yield, decreases
in production and an estimated sixty million or more additional people
at risk of hunger as a result of climate change.
The authors emphasise that, although the models and the methods
they have employed are comparatively complex, there are many fac-
tors that have not been taken into account. For instance, they have not
adequately considered the impact of changes in climate extremes, the
availability of water supplies for irrigation or the effects of future tech-
nological change on agricultural productivity. Further (see Chapter 6),
scientists are not yet very confident in the regional detailof climate
change. The results, therefore, although giving a general indication of
the changes that could occur, should not be treated as a detailed predic-
tion. They highlight the importance of studies of this kind as a guide to
future action.