|August 2007, Ariel Dinar
A recent cross-country study using the Ricardian1 approach shows that the effects of climate change on the African continent may force large regions of marginal agriculture out of production by the end of this century, while helping others.
The study highlights the importance of equipping millions of agriculture-dependent and water-deprived Africans in the most vulnerable countries with the information, technologies, and supporting institutions they need to adapt to further climate deterioration.
Even without climate change, African agriculture faces serious challenges—land degradation, inadequate irrigation, rural-to-urban migration, political instability, and stagnant economies. Slow technological progress and a lack of access to information on how to cope with climate change are further constraints.2
A recent study3 the first to analyze climate impact and adaptation across the African continent and to combine cross-country observed and simulated data—provides economic insights into the magnitude of the impact and the value of adaptation, both of which are necessary for policy makers to undertake and prioritize among policy interventions.
The results suggest that Africa will be hit hard by severe climate change under various scenarios. Some countries are more vulnerable than others, so it is important to focus help where it is needed most. In several scenarios, many African farmers gain, whereas others lose.4
A simple scientific background
Agricultural production is sensitive to climate because it depends, for its production process, on heat for energy and on water, both climate-related variables. Too much heat and too much water—or too little—will hamper growing conditions. There is an optimal range of climate within which production is maximized.
Farmers can reduce crop and livestock sensitivity to climate variables by introducing new technologies and management practices. Better-equipped farmers can adapt to and survive inferior climates, as shown in the figure to the right.
The study uses spatially referenced socio-economic household survey, climatic, and soil data, across key agro -climatic zones and farming systems, in addition to river-basin hydrology modeling that generated spatially referenced surface runoff and stream flow.
Cross section models allow quantitative estimates of the economic impact of climate change in sampled locations in each country. For these models, baseline data for climate, agricultural production, and water flow were collected for each sampled district in each country.
This data allowed comparison of the economic performance of farms facing different climate and water supplies. Comparing farm net incomes across climates, the climate sensitivity of current farms was estimated in each country. This information was then used to predict the long-run impacts of both small changes in climate and future climate scenarios.
Pulling observations from across the continent permitted region-wide analyses with extrapolations to any location in Africa. Two types of analyses were conducted. First, a marginal impact was estimated, using only the cross sectional coefficients. Then, an analysis involving predicted climate scenarios provided more comprehensive estimates of impact.
Of the two scenarios considered, the first was a uniform change across the country and the second involved specific climate scenarios from Global Circulation Models (GCMs). Three different GCM scenarios by 2100 explore the consequences of a range of climate changes considered plausible by climate scientists.
Results based on economic and hydrologic frameworks
The range of possible Africa-wide climate change impacts on stream flow (by countries) increases significantly between 2050 and 2100 (the 2100 scenario), as shown in the figures below:
Source: Strzepek and McCluskey, "The Impacts of Climate Change on Regional Water Resources and Agriculture in Africa," Policy Research Working Paper 4290, World Bank, Washington, DC. Larger image
For rainfed farms, evaluated at their mean temperature, net revenues fall by $27/˚C. In contrast, the marginal effect of temperature on irrigated farms, evaluated at their mean temperature, is a positive $35/˚C . Warmer temperatures increase the net revenues of irrigated farms because the mean temperature in regions with irrigated farms is relatively cool and because irrigation buffers net revenues from temperature effects.
The marginal precipitation effects for rainfed and irrigated farms are more similar ($3.8/mm/mo for irrigated farms and $2.7/mm/mo for rainfed). The relatively high response of irrigated farms to precipitation is due to their current dry location.
In uniform climate change impact scenarios for Africa (2.5 and 5˚C temperature increase and 7 and 14 percent precipitation decrease), values per hectare and the total Africa impact suggest a big loss for rainfed agriculture if temperature increases. However, irrigated agriculture gains from rising temperatures as shown in the table below:
Net revenue impacts from uniform climate scenarios
increase of 2.5°C
increase of 5°C
Precipitation decrease of 7%
Precipitation decrease of 14%
($ per ha)
ΔTotal net revenue
($ per ha)
ΔTotal net revenue
Total (Africa )
($ per ha)
ΔTotal net revenue
Note: Values in parenthesis represent percentage changes from present climate.
Source: Kurukulasuriya and Mendelsohn, "A Ricardian Analysis of the Impact of Climate Change on African Cropland," Policy Research Working Paper 4305, World Bank, Washington, DC.
Climate scenarios for 2100 as predicted by several Global Circulation Models allowed testing of non-marginal changes in climate assuming nothing else changes. The results show that net revenues from crops will rise in a mild wet scenario by as much as $90 billion across Africa, while a very hot scenario could lead to losses of $48 billion by 2100.
Despite these aggregate impacts, irrigated farms are predicted to generally benefit because they are climate insensitive and located in relatively cool places. Rainfed farms are likely to be affected the most whether in terms of benefits or losses.
- Different effects on large and small livestock farms
Net revenues for small livestock farms increase with warming by 25 to 58 percent. The net revenues of large livestock owners, however, tend to fall except in a very dry scenario.
Small farms can substitute animals that are heat tolerant, whereas large farms are more dependent on species, such as cattle, that are less heat tolerant. Wetter scenarios imply a shift from grasslands to forests, an increase in harmful disease vectors, and a shift from livestock to crops.
Overall the livestock sector in Africa loses from climate change because most animals are raised on large farms. While livestock earnings for small farmers increase with warming these gains are generally smaller than the losses they face from crops.
- Adaptation policies must take crop selection into account
The results strongly suggest that adaptation policies to climate change must take into account crop selection. There is an important role for agronomic research in developing new varieties more suited for higher temperatures.
Source: Kurukulasuriya and Mendelsohn, "Crop Selection: Adapting to Climate Change in Africa," Policy Research Working Paper 4307, World Bank, Washington, DC.
Although income from agriculture in Africa will still suffer losses, these will be much smaller if farmers are not confined to their current set of options.
Source: Seo and Mendelsohn, 2007, “ The Impact of Climate Change on Livestock Management in Africa: A Structural Ricardian Analysis,” Policy Research Working Paper 4279, World Bank, Washington, DC. Larger image
Managing livestock in Africa is likely to be relatively more profitable than crops under future climate conditions. However, the mix of species chosen will be slightly different than today.
Farmers just south of the Sahara will switch species, diversify their portfolio, and move from cattle toward sheep. Small farmers will adapt without much change in expected net income, but large sheep farmers in South Africa will have to abandon sheep as the area suitable for sheep farming will shrink as climate changes. These changes are predicted to reduce the net incomes of large farms considerably, as shown above.
- Irrigation is an effective remedy where surface water is available
|Source: Kurukulasuria and Mendelsohn . 2007. “Endogenous Irrigation: The Impact of Climate Change on Farmers in Africa.” Policy Research Working Paper 4278, World Bank, Washington, DC. |
Irrigation is an effective adaptation against reduction in rainfall and higher temperatures will be an effective remedy in select regions of Africa with water as shown in the figure to the right/left. However, for many regions, there is no available surface water, so that warming scenarios with reduced rainfall are particularly deleterious.
Ariel Dinar is a Lead Economist in the Development Research Group (Sustainable Rural and Urban Development Team). His research interests include the economics of water resources and climate change.
1.The Ricardian technique, named after David Ricardo (1772-1823), is used to estimate the net productivity of farmland measured either in land value or net income per unit of land. It uses statistical regression to estimate the contribution of different production factors such as environment (e.g., soil quality), purchased inputs (e.g., machinery, chemicals, labor) and support systems (e.g., infrastructure and institutions) to net productivity.
2. This research brief is based on a forthcoming book The Policy Nexus of Agriculture and Global Climate Change in Africa, by Ariel Dinar, Rashid Hassan, Robert Mendelsohn, and James Benhin, London: EarthScan; and journal article "Will African Agriculture Survive Climate Change?" Pradeep Kurukulasuriya , Robert Mendelsohn, Rashid Hassan, James Benhin, Temesgen Deressa, Mbaye Diop, Helmy Mohamed Eid, K. Yerfi Fosu, Glwadys Gbetibouo, Suman Jain, Ali Mahamadou, Renneth Mano, Jane Kabubo-Mariara, Samia El-Marsafawy, Ernest Molua, Samiha Ouda, Mathieu Ouedraogo, Isidor Séne, David Maddison, S. Niggol Seo, and Ariel Dinar, World Bank Economic Review 20(3):367-388, 2006.
3. The study focused on 11 African countries (Burkina Faso, Cameroon, Ghana, Niger and Senegal in west Africa; Egypt in north Africa; Ethiopia and Kenya in east Africa; and South Africa, Zambia, and Zimbabwe in southern Africa). It was funded by the Global Environment Facility/World Bank and coordinated by the Center for Environmental Economics and Policy in Africa, University of Pretoria, South Africa. Project website: http://www.ceepa.co.za/Climate_Change/index.html.
4. For related working papers on the effects of climate change on agriculture in Africa see Seo and Mendelsohn , “Climate Change Adaptation in Africa: A Microeconomic Analysis of Livestock Choice,” Policy Research Working Paper 4277, World Bank, Washington, DC, 2007; Kurukulasuriya and Mendelsohn , “Endogenous Irrigation: The Impact of Climate Change on Farmers in Africa,” Policy Research Working Paper 4278, World Bank, Washington, DC; and Seo and Mendelsohn, “The Impact of Climate Change on Livestock Management in Africa: A Structural Ricardian Analysis,” Policy Research Working Paper 4279, World Bank, Washington, DC, 2007.