Climatic Change Impacts

Possible impacts for the world from one study are illustrated in Table 21.1 (Darwin et al., 1995). Without adaptation, cereal production was estimated to fall globally by 19-29%. With farm-level, market and land use adaptation, there is potential to reduce these losses substantially so that impact on cereal production ranges between ± 1%. This study is based on an analogous region method. The initial impact on cereal production compares very closely to work by Rosenzweig and Parry (1994). The Darwin study differs in that adaptation is estimated as able to offset completely the yield losses at a global level. Issues remain with regard to whether the full potential for adaptation can be realized. These results do not include an adjustment for the possible beneficial effect of CO2 fertilization. Both of these efforts relate agricultural economic impacts to a global model of the entire world economy. The Darwin et al. approach also

Table 21.1. Percentage changes in the supply3 and production of cereals for the world by climate change scenario. (Source: Darwin et al., 1994.)

General circulation model (GCM)

Supply

Production

No adaptation Land use fixed Land use fixed No restrictions

Table 21.1. Percentage changes in the supply3 and production of cereals for the world by climate change scenario. (Source: Darwin et al., 1994.)

General circulation model (GCM)

Supply

Production

No adaptation Land use fixed Land use fixed No restrictions

GISSb

-22.6

-2.4

0.2

0.9

GFDLc

-23.5

-4.4

-0.6

0.3

UKMOd

-29.3

-6.4

-0.2

1.2

OSUe

-18.6

-3.9

-0.5

0.2

aChanges in supply represent the additional quantities that firms would be willing to sell at 1990 prices under the alternative climate. Changes in production are changes in equilibrium quantities.

bGISS = Goddard Institute for Space Studies.

cGFDL = Geophysical Fluid Dynamics Laboratory.

dUKMO = UK Meteorological Office.

eOSU = Oregon State University.

aChanges in supply represent the additional quantities that firms would be willing to sell at 1990 prices under the alternative climate. Changes in production are changes in equilibrium quantities.

bGISS = Goddard Institute for Space Studies.

cGFDL = Geophysical Fluid Dynamics Laboratory.

dUKMO = UK Meteorological Office.

eOSU = Oregon State University.

Table 21.2. Regional crop yield for 2 x CO2 GCM equilibrium climates. (Source: Reilly et al, 1996.)

Region

Crop

Yield impact (%)

i Countries studied/comments

Latin

Maize

-61 to increase

Argentina, Brazil, Chile, Mexico. Range is

America

across GCM scenarios, with and without

the CO2 effect

Wheat

-50 to -5

Argentina, Uruguay, Brazil. Range is across

GCM scenarios, with and without the CO2

effect

Soybean

-10 to +40

Brazil. Range is across GCM scenarios,

with CO2 effect

Former

Wheat

-19 to +41

Range is across GCM scenarios and region,

Soviet

Grain

-14 to +13

with CO2 effect

Union

Europe

Maize

-30 to increase

France, Spain, N. Europe. With adaptation,

CO2 effect. Longer growing season;

irrigation efficiency loss; northward shift

Wheat

Increase or

France, UK, N. Europe. With adaptation,

decrease

CO2 effect. Longer season: northward shift;

greater pest damage; lower risk of crop

failure

Vegetables

Increase

North

Maize

-55 to +62 1

USA and Canada. Range across GCM

America

Wheat

-100 to +234J

scenarios and sites; with/without CO2 effect

Soybean

-96 to +58

USA. Less severe or increase in yield when

CO2 effect and adaptation considered

Africa

Maize

-65 to +6

Egypt, Kenya, South Africa, Zimbabwe.

With CO2 effect, range across sites and

climate scenarios

Millet

-79 to -63

Senegal. Carrying capacity fell by 11-38%

Biomass

Decrease

South Africa; agrozone shifts

South Asia

Rice

-22 to +28 1

Bangladesh, India, Philippines, Thailand,

Maize

-65 to -10 1

Indonesia, Malaysia, Myanmar. Range over

Wheat

-61 to +67 J

GCM scenarios, and sites; with CO2 effect;

some studies also consider adaptation

Mainland

Rice

-78 to +28

Includes rain-fed and irrigated rice. Positive

China and

effects in NE and NW China, negative in

Taiwan

most of the country. Genetic variation

provides scope for adaptation

Other Asia

Rice

-45 to +30

Japan and South Korea. Range is across

and Pacific

GCM scenarios. Generally positive in

Rim

northern Japan; negative in south

Pasture

-1 to +35

Australia and New Zealand. Regional

variation

Wheat

-41 to +65

Australia and Japan. Wide variation,

depending on cultivar

includes, in a crude way, water supply change impacts and competition for water and land resources from other sectors, but the modelling effort imposes climatic change on the world economy as it exists today. Rosenzweig and Parry (1994) estimate climatic impacts under a 2 x CO2 world and linearly impose these changes through time (assuming the full effect occurs in 2060) in an economic model where economies grow and change through time.

Yield impact studies using crop response models have been conducted for many countries. Table 21.2 summarizes the basic findings. Results vary widely, depending on the climatic scenario, methods and particular site examined. All studies tend to show negative impacts for equatorial and subtropical regions, while areas nearer the poles often show improved cropping conditions. Beyond these broad regional patterns, which appear to be observed in most studies, greater details on regional impacts generally do not hold up across different climatic scenarios.

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