The IBSNAT models were selected for this study because they have been
validated over a wide range of environments and are not specific to any
particular location or soil type. They are thus suitable for use in large-area studies
in which crop growing conditions differ greatly. The validation of the crop
models over different environments also improves the ability to estimate effects of
changes in climate. Furthermore, because management practices, such as the
choice of varieties, planting date, fertilizer application and irrigation may be
varied in the models, they permit experiments that simulate adjustments by
farmers and agricultural systems to climate change.
Physiological effects of CO 2 . Most plants growing in experimental environments
with increased levels of atmospheric CO
exhibit increased rates of net
photosynthesis (i.e. total photosynthesis minus respiration) and reduced stomatal
opening. By so doing, CO
reduces transpiration per unit leaf area while
enhancing photosynthesis. Thus, it often improves water-use efficiency (the ratio
of crop biomass accumulation or yield to the amount of water used in
evapotranspiration). The crop models used in this study account for the beneficial
physiological effects of increased atmospheric CO
concentrations on crop
growth and water use. —
Limitations of crop growth models. The crop growth models embody a number
of simplifications. For example, weeds, diseases and insect pests are assumed to be
controlled, there are no problem soil conditions (e.g. high salinity or acidity), and
there are no extreme weather events such as heavy storms. The crop models
simulate the current range of agricultural technologies available around the
world. They do not include induced improvements in such technology, but may
be used to test the effects of some potential improvements, such as varieties with
higher thermal requirements and the installation of irrigation systems.
Yield simulations. Crop modelling simulation experiments were performed at
112 sites in 18 countries for the baseline climate (1951—80) and the GCM-doubled
S. Otter-Nacke, D. C. Godwin and J. T. Ritchie, Testing and Validating the CERES-Wheat Model
in Diverse Environments, AGGRISTARS YM-15-00407, Johnson Space Center No. 20244,
Houston, 1986.
B. Acock and L. H. Allen, Crop responses to elevated carbon dioxide concentrations, in B. R.
Strain and J. D. Cure, (eds.), Direct Effects of Increasing Carbon Dioxide on Vegetation, US
Department of Energy, Washington, DC, DOE/ER-0238, 1985, pp. 33—97.
J. D. Cure, Carbon dioxide doubling responses: a crop survey, in B. R. Strain and J. D. Cure, (eds.),
Direct Effects of Increasing Carbon Dioxide on Vegetation, US Department of Energy, Washington,
DC, DOE/ER-0238, 1985, pp. 33—97.
B. A. Kimball, Carbon dioxide and agricultural yield. An assemblage and analysis of 430 prior
observations, Agron. J., 1983, 75, 779—788.
H. H. Rogers, G. E. Bingham, J. D. Cure, J. M. Smith and K. A. Surano, Responses of selected plant
species to elevated carbon dioxide in the field, J. Environ. Qual., 1983, 12, 569—574.
J. D. Cure and B. Acock, Crop responses to carbon dioxide doubling: a literature survey, Agric.
Forest Meteorol., 1986, 38, 127—145.
L. H. Allen, Jr., K. J. Boote, J. W. Jones, P. H. Jones, R. R. Valle, B. Acock, H. H. Rogers and R. C.
Dahlman, Response of vegetation to rising carbon dioxide: photosynthesis, biomass and seed yield
of soybean, Global Biogeochem. Cycles, 1987, 1, 1—14.
R. M. Peart, J. W. Jones, R. B. Curry, K. Boote and L. H. Allen, Jr., Impact of climate change on
crop yield in the south-eastern USA, in J. B. Smith and D. A. Tirpak (eds.), The Potential Effects of
Global Climate Change on the United States, US Environmental Protection Agency, Washington,
DC, 1989.
M. Parry and M. Livermore
112
validated over a wide range of environments and are not specific to any
particular location or soil type. They are thus suitable for use in large-area studies
in which crop growing conditions differ greatly. The validation of the crop
models over different environments also improves the ability to estimate effects of
changes in climate. Furthermore, because management practices, such as the
choice of varieties, planting date, fertilizer application and irrigation may be
varied in the models, they permit experiments that simulate adjustments by
farmers and agricultural systems to climate change.
Physiological effects of CO 2 . Most plants growing in experimental environments
with increased levels of atmospheric CO
exhibit increased rates of net
photosynthesis (i.e. total photosynthesis minus respiration) and reduced stomatal
opening. By so doing, CO
reduces transpiration per unit leaf area while
enhancing photosynthesis. Thus, it often improves water-use efficiency (the ratio
of crop biomass accumulation or yield to the amount of water used in
evapotranspiration). The crop models used in this study account for the beneficial
physiological effects of increased atmospheric CO
concentrations on crop
growth and water use. —
Limitations of crop growth models. The crop growth models embody a number
of simplifications. For example, weeds, diseases and insect pests are assumed to be
controlled, there are no problem soil conditions (e.g. high salinity or acidity), and
there are no extreme weather events such as heavy storms. The crop models
simulate the current range of agricultural technologies available around the
world. They do not include induced improvements in such technology, but may
be used to test the effects of some potential improvements, such as varieties with
higher thermal requirements and the installation of irrigation systems.
Yield simulations. Crop modelling simulation experiments were performed at
112 sites in 18 countries for the baseline climate (1951—80) and the GCM-doubled
S. Otter-Nacke, D. C. Godwin and J. T. Ritchie, Testing and Validating the CERES-Wheat Model
in Diverse Environments, AGGRISTARS YM-15-00407, Johnson Space Center No. 20244,
Houston, 1986.
B. Acock and L. H. Allen, Crop responses to elevated carbon dioxide concentrations, in B. R.
Strain and J. D. Cure, (eds.), Direct Effects of Increasing Carbon Dioxide on Vegetation, US
Department of Energy, Washington, DC, DOE/ER-0238, 1985, pp. 33—97.
J. D. Cure, Carbon dioxide doubling responses: a crop survey, in B. R. Strain and J. D. Cure, (eds.),
Direct Effects of Increasing Carbon Dioxide on Vegetation, US Department of Energy, Washington,
DC, DOE/ER-0238, 1985, pp. 33—97.
B. A. Kimball, Carbon dioxide and agricultural yield. An assemblage and analysis of 430 prior
observations, Agron. J., 1983, 75, 779—788.
H. H. Rogers, G. E. Bingham, J. D. Cure, J. M. Smith and K. A. Surano, Responses of selected plant
species to elevated carbon dioxide in the field, J. Environ. Qual., 1983, 12, 569—574.
J. D. Cure and B. Acock, Crop responses to carbon dioxide doubling: a literature survey, Agric.
Forest Meteorol., 1986, 38, 127—145.
L. H. Allen, Jr., K. J. Boote, J. W. Jones, P. H. Jones, R. R. Valle, B. Acock, H. H. Rogers and R. C.
Dahlman, Response of vegetation to rising carbon dioxide: photosynthesis, biomass and seed yield
of soybean, Global Biogeochem. Cycles, 1987, 1, 1—14.
R. M. Peart, J. W. Jones, R. B. Curry, K. Boote and L. H. Allen, Jr., Impact of climate change on
crop yield in the south-eastern USA, in J. B. Smith and D. A. Tirpak (eds.), The Potential Effects of
Global Climate Change on the United States, US Environmental Protection Agency, Washington,
DC, 1989.
M. Parry and M. Livermore
112