Climate Change

Tremendous variation exists in average yields of major food crops among industrialized countries. Yields in these countries are higher by a factor of 7 to 8 than in developing countries. Data in Table 5.5 show that national average wheat yields range from a low of 0.8 MT/ha in Kazakhstan to a high of 7.8 MT/ha in the United Kingdom. Similarly, yields of maize range from a low of 1.3 MT/ha in Nigeria to a high of 9.4 MT/ha in Italy. In addition to these large yield variations, a large gap exists between actual yield and attainable yield,

Table 5.5 Average Yield of Maize and Wheat in Countries That Produce 90% of Global Output (MT/ha)

Country Wheat Yield Maize Yield

Argentina 2.4 5.0

Canada 2.4 7.4

France 7.0 8.6

Hungary 3.9 6.0

Romania 2.6 3.0

United States 2.7 8.2

Source: Modified from Bruinsma, J., Ed. 2003. World Agriculture: Towards 2015/2030. Food and Agriculture Organization, Rome; Earthscan, London.

and this gap is larger in developing than in industrialized countries. As seen in Table 5.6, the gap in wheat yield is 4.2 MT/ha in Belarus; 4.0 MT/ha in Lithuania; 3.8 MT/ha in

Table 5.6 Actual and Attainable Wheat Yield in 25 Countries (MT/ha)

Country Attainable Yield Actual Yield

Table 5.6 Actual and Attainable Wheat Yield in 25 Countries (MT/ha)

Argentina

4.2

2.4

Australia

4.2

2.0

Belarus

6.7

2.5

Brazil

3.3

1.8

Canada

4.3

2.4

Ethiopia

4.0

1.2

France

6.6

7.1

Germany

7.6

7.3

Hungary

6.4

3.9

Italy

6.5

3.2

Japan

7.1

3.4

Latvia

6.2

2.5

Lithuania

6.8

2.8

Myanmar

2.5

0.9

Paraguay

3.4

1.4

Poland

7.1

3.4

Romania

6.3

2.5

Russia

4.4

1.4

Sweden

5.0

6.0

Tanzania

3.0

1.5

Turkey

4.8

2.1

Ukraine

6.2

2.5

United Kingdom

6.7

7.8

United States

5.8

2.7

Uruguay

5.3

2.3

Source: Modified from Bruinsma, J., Ed. 2003. World Agriculture: Towards 2015/2030. Food and Agriculture Organization, Rome; Earthscan, London.

Source: Modified from Bruinsma, J., Ed. 2003. World Agriculture: Towards 2015/2030. Food and Agriculture Organization, Rome; Earthscan, London.

Romania; 3.7 MT/ha in Latvia, Poland, and Ukraine; and 3.0 MT/ha in Uruguay. These estimates may, however, be affected by climate change, resulting in even lower yields and larger yield gaps.

Rosenzweig and Parry (1993) projected overall decrease in crop yields both with and without CO2 effects. The projected decrease in crop yields without CO2 fertilization effects ranged from -16% to -33% for wheat, -24% to -25% for rice, -20% to -31% for maize, and -19% to -57% for soybeans. In comparison, the projected decrease in crop yields with CO2 effects ranged from -13% to 11% for wheat, -2% to -5% for rice, -15% to -24% for maize, and -33% to 16% for soybeans. Apparently, wheat and soybean yields may increase because of a CO2 fertilization effect, provided that other factors such as soil quality remain the same.

There are numerous uncertainties in predicting the effects of CO2 enrichment on plants. Short-term gains in photosynthesis due to CO2 fertilization may be much greater than long-term effects, especially for C3 plants (Wolfe and Erick-son, 1993). Relative crop responses to CO2 fertilization also depend on ambient temperature (Idso et al., 1987), soil/water regime (Gifford, 1979), nutrient availability (Allen, 1991), and other factors such as weed competition and disease and insect pressure (Wolfe and Erickson, 1993). Consequently, projections must remain quite tentative for now.

Anticipated effects of climate change on maize yield in Zimbabwe are shown in Table 5.7. These three scenarios are under current climate, altered climate, and altered weather with CO2 enrichment effect. Changes in maize yields were estimated using three separate models. Maize yields under all three conditions declined with climate change both with and without the CO2 enrichment effect. The average decline in maize yield in comparison with a base yield of 3.7 MT/ha was 50% without any adaptive management option, 42% with additional fertilizer use, and 13% with additional fertilizer and irrigation use (Muchena and Iglesias, 1995; Parry and Carter, 1998).

Reilly (2002) reported an assessment of potential impacts of climate change on U.S. agriculture during the 21st century using various scenarios. A decline in the yield of wheat and sugarcane crops could be mostly alleviated by better management, but the latter would not significantly affect yield reduction in potatoes. The World Bank (1998) studied the impact of climate change on Indian agriculture. This report concluded that CO2 fertilization could offset the harmful effects of climate change so that crop yields would be only marginally affected. According to Dinar and Mendelsohn (1998), adaptive management could mitigate any additional harmful effects,

Table 5.7 Effects of Projected Climate Change and Adaptive Management on Maize Yield in Zimbabwe

Global Circulation Model-Based Climatic Scenarios (MT/ha)

Table 5.7 Effects of Projected Climate Change and Adaptive Management on Maize Yield in Zimbabwe

Global Circulation Model-Based Climatic Scenarios (MT/ha)

Location

GISS

GFDL

UKMO

Blanket

Base

4.S

4.S

4.S

Climate change

3.9

4.2

3.6

Climate change with direct CO2

effect

4.1

4.4

3.7

Chisumbanje

Base

2.S

2.S

2.S

Climate change

2.1

2.1

1.S

Climate change with direct CO2

effect

2.2

2.2

1.9

Gweru

Base

3.7

3.7

3.7

Climate change

2.6

2.7

1.S

Climate change with direct CO2

effect

3.1

3.3

2.0

Soure: Modified from Parry, M. and T. Carter. 1998. Climate Impact and Adaptation Assessment: A Guide to the IPCC Approach. Earthscan, London. With permission. GFDL, Geophysical Fluid Dynamics Laboratory model; GISS, Goddard Institute for Space Studies model; UKMO, United Kingdom Meteorological Office model.

Soure: Modified from Parry, M. and T. Carter. 1998. Climate Impact and Adaptation Assessment: A Guide to the IPCC Approach. Earthscan, London. With permission. GFDL, Geophysical Fluid Dynamics Laboratory model; GISS, Goddard Institute for Space Studies model; UKMO, United Kingdom Meteorological Office model.

although this prediction is subject to the same uncertainty as predictions of negative consequences.

The adverse impacts of climate change on agriculture in general and on crop yields in particular under most scenarios are likely to be severe for the countries of Sub-Saharan Africa where institutional support to enable use of adaptive management is minimal, and where soil resources are already degraded because of long-term land misuse, soil mismanagement, and exploitative agricultural practices. The economic impact of extreme climate events may be more severe in semiarid regions of less developed countries than in cool temperate and cold regions (Parry and Carter, 1988a, 1988b). Indeed, some extreme climate scenarios predict regional disasters in food production even if global production is not affected. Furthermore, the impacts of climate change on crop yields have only been studied for principal crops such as wheat, rice, soybeans, and potatoes. Little if any research has been done on regional crops, especially those of importance to small landholders in Africa and elsewhere in the tropics, such as yam, cassava, and millet.

Was this article helpful?

0 0

Post a comment