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 7.12.45

A climate change scenario is fi rst 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 carbon dioxide are applied to 124 different locations in 18 countries to produce projected crop yields that 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 investment, reallocation of agricultural resources according to economic returns (including crop switching) and reclamation of additional arable land as a response to higher cereal prices. The outputs from the total process provide information projected up to the 2080s on food production, food prices and the number of people at risk of hunger (defined as the population with an income insufficient either to produce or to procure their food requirements).

The main results with models of this kind for the 2080s regarding the impact of climate change, for SRES scenarios A1, B1 or B2, are that yields at mid to high latitudes are expected to increase, and at low latitudes (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 more 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 factors 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 technological change on agricultural productivity. Further (see Chapter 6), scientists have as yet limited confidence in the regional detail of climate change. The results, therefore, although giving a general indication of the changes that could occur, should not be treated as a detailed prediction. They highlight the importance of studies of this kind as a guide to future action.

Trace gases

Climate models

Observed climate

Figure 7.12 Key elements of a study of crop yield and food trade under a changed climate.

Climate change scenarios

Sensitivity tests

CO2 effects

Crop models: wheat, rice, maize, soya bean

Crop yield by site and scenario: evapotranspiration, irrigation, season length

Aggregation of site results Agroecological zone analysis i

Yield functions by region Yield = function of temperature precipitation and Co2

Yield change estimates Commodity group and country/region

Technology projections

Economic growth rates

World food trade model


Economic consequences

Shifts in trade Incidence of food poverty

Farm-level adaptations

Population trends



Wheat, mid- to high latitude

Wheat, low latitude

Wheat, mid- to high latitude

Mean local temperature change (°C)

Mean local temperature change (°C)

Mean local temperature change (°C)

Mean local temperature change (°C)

Figure 7.11 Sensitivity of yield to climate change for wheat for mid to high latitude (a) and low latitude (b). Cases without adaptation (red) and with adaptation (green). Derived from 69 published studies at multiple simulation sites.

that in many developing countries (where large increases in population are occurring) is likely to decline as a result of climate change. The disparity between developed and developing nations will tend to become much larger, as will the number of those at risk of hunger. The surplus of food in developed countries is likely to increase, while developing countries will face increasing deprivation as their declining food availability becomes much less able to provide for the needs of their increasing populations. Such a situation will raise enormous problems, one of which will be that of employment. Agriculture is the main source of employment in developing countries; people need employment to be able to buy food. With changing climate, as some agricultural regions shift, people will tend to attempt to migrate to places where they might be employed in agriculture. With the pressures of rising populations, such movement is likely to be increasingly difficult and we can expect large numbers of environmental refugees.

In looking to future needs, two activities that can be pursued now are particularly important. Firstly, there is a large need for technical advances in agriculture in developing countries requiring investment and widespread local training. In particular, there needs to be continued development of programmes for crop breeding and management, especially in conditions of heat and drought. These can be immediately useful in the improvement of productivity in marginal environments today. Secondly, as was seen earlier when considering fresh water supplies, improvements need to be made in the availability and management of water for irrigation, especially in arid or semi-arid areas of the world.

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