middle of the 2080s.
The end result is that the estimates of future warming have been greatly
reduced from more than 5 °C by 2060 to less than 3.5 °C by the middle of the
2080s. In response to this and changes in the environmental and socio-economic
systems the latest estimates regarding future world food security are far more
modest. Changes in yield now range from 910% to ;10%. While much smaller
than the earlier estimates they are still considerable impacts when seen in the
context of the world food trade market.
The research method has also changed slightly. In the latest suite of
experiments the crop models were run for current climate conditions and for
three future climate conditions predicted by the Hadley Centre’s GCMs known
as HadCM2. All climate change scenarios are based on an IS92a-type
forcing (one which assumes greenhouse gas emissions stem from a ‘business-as-usual’
future in economic and social terms).
Estimated Effects on Yields
Figures 6a—c show the estimated potential changes in average national grain crop
yields for the four HadCM2 and one HadCM3 climate change scenarios,
allowing for the direct effects of CO
on plant growth. The maps are created from
the nationally averaged yield changes for wheat, rice and maize. Regional
variations within countries are not shown.
The latitudinal variations in crop yields illustrated in Figures 6a—c are mainly
due to differences in current growing conditions. Under the HadCM2 scenario, in
many mid- and high-latitude areas, where current temperature regimes are low,
the increase in surface temperatures tends to lengthen the growing season thus
increasing yields. This potentially beneficial effect is not evident under the
HadCM3 scenario. The intensified polar warming experienced under HadCM3 is
so great that the threshold concerning positive effects of warmer temperatures at
higher latitudes is exceeded and a decrease in yields occurs in some of these regions.
Another difference evident from Figures 6a—c is that, while the area most
adversely affected under HadCM2 is the Indian subcontinent, under HadCM3 it
is western Africa and the USA.
Estimated Effects on Food Production, Food Prices and Risk of
Hunger
The reference scenario (the future without climate change). Assuming no effects of
climate change on crop yields and current trends in economic and population
E. Bos, T. My, E. M. Vu and R. A. Bulatao, World Population Projections 1994—95: Estimates and
Projections with Related Demographic Statistics, World Bank, Johns Hopkins University Press,
New York, 1994.
C. Rosenzweig, M. L. Parry, G. Fischer and K. Frohberg, Climate Change and World Food Supply,
Research Report No. 3, Environmental Change Unit, University of Oxford, Oxford, 1993.
J. F. B. Mitchell, T. C. Johns, J. M. Gregory and S. Tett, Climate response to increasing levels of
greenhouse gases and sulphate aerosols, Nature, 1995, 376, 501—504.
M. Hulme, J. Mitchell, W. Ingram, T. Johns, M. New and D. Viner, Climate Change Scenarios for
Global Impacts Studies, Global Environ. Change, 1999, 9, (4), s3—s19.
M. Parry and M. Livermore
124
The end result is that the estimates of future warming have been greatly
reduced from more than 5 °C by 2060 to less than 3.5 °C by the middle of the
2080s. In response to this and changes in the environmental and socio-economic
systems the latest estimates regarding future world food security are far more
modest. Changes in yield now range from 910% to ;10%. While much smaller
than the earlier estimates they are still considerable impacts when seen in the
context of the world food trade market.
The research method has also changed slightly. In the latest suite of
experiments the crop models were run for current climate conditions and for
three future climate conditions predicted by the Hadley Centre’s GCMs known
as HadCM2. All climate change scenarios are based on an IS92a-type
forcing (one which assumes greenhouse gas emissions stem from a ‘business-as-usual’
future in economic and social terms).
Estimated Effects on Yields
Figures 6a—c show the estimated potential changes in average national grain crop
yields for the four HadCM2 and one HadCM3 climate change scenarios,
allowing for the direct effects of CO
on plant growth. The maps are created from
the nationally averaged yield changes for wheat, rice and maize. Regional
variations within countries are not shown.
The latitudinal variations in crop yields illustrated in Figures 6a—c are mainly
due to differences in current growing conditions. Under the HadCM2 scenario, in
many mid- and high-latitude areas, where current temperature regimes are low,
the increase in surface temperatures tends to lengthen the growing season thus
increasing yields. This potentially beneficial effect is not evident under the
HadCM3 scenario. The intensified polar warming experienced under HadCM3 is
so great that the threshold concerning positive effects of warmer temperatures at
higher latitudes is exceeded and a decrease in yields occurs in some of these regions.
Another difference evident from Figures 6a—c is that, while the area most
adversely affected under HadCM2 is the Indian subcontinent, under HadCM3 it
is western Africa and the USA.
Estimated Effects on Food Production, Food Prices and Risk of
Hunger
The reference scenario (the future without climate change). Assuming no effects of
climate change on crop yields and current trends in economic and population
E. Bos, T. My, E. M. Vu and R. A. Bulatao, World Population Projections 1994—95: Estimates and
Projections with Related Demographic Statistics, World Bank, Johns Hopkins University Press,
New York, 1994.
C. Rosenzweig, M. L. Parry, G. Fischer and K. Frohberg, Climate Change and World Food Supply,
Research Report No. 3, Environmental Change Unit, University of Oxford, Oxford, 1993.
J. F. B. Mitchell, T. C. Johns, J. M. Gregory and S. Tett, Climate response to increasing levels of
greenhouse gases and sulphate aerosols, Nature, 1995, 376, 501—504.
M. Hulme, J. Mitchell, W. Ingram, T. Johns, M. New and D. Viner, Climate Change Scenarios for
Global Impacts Studies, Global Environ. Change, 1999, 9, (4), s3—s19.
M. Parry and M. Livermore
124