yield and agriculture were considered. Adaptation Level 1 included those
adaptations at the farm level that would not involve any major changes in
agricultural practices. It thus took account of changes in planting date, amounts
of irrigation and the choice of crop varieties that are currently available.
Adaptation Level 2 encompassed, in addition to the former, major changes in
agricultural practices, such as large shifts of planting date, the availability of new
cultivars, extensive expansion of irrigation and increased fertilizer application.
This level of adaptation would be likely to involve policy changes both at the
national and international level and significant costs. However, policy, cost and
water were not studied explicitly.
Scenarios of different future trade, economic and population growth. A final set of
scenarios assumed changes to the world tariff structure and different rates of
growth of economy and population. As with previous experiments, these were
conducted both with and without climate change impacts. These scenarios included:
E Full trade liberalization. Full trade liberalization in agriculture introduced
gradually by 2020.
E Lower economic growth (ranging from 2.7% per year in 1980—2000 to 1.0%
in 2040—2060). Global GDP in 2060 is 10.3% lower than the reference
scenario, 11.2% lower in developing countries and 9.8% lower in developed
countries.
E Low population growth. UN low population estimates (ca. 8.6 billion by 2060).
Effects on Yields
The results show that climate change scenarios excluding the direct physiological
effects of CO
predict decreases in simulated yields in many cases, while the direct
effects of increasing atmospheric CO
mitigate the negative effects primarily in
mid- and high-latitudes. The differences between countries in yield responses to
climate change are related to differences in current growing conditions. At low
latitudes crops are grown nearer the limits of temperature tolerance and global
warming may subject them to higher stress. In many mid- and high-latitude areas,
increasing temperatures may benefit crops otherwise limited by cold temperatures
and short growing seasons in the present climate.
The primary causes of decreases in yield are:
1. Shortening of the growing period (especially the grain filling stage) of the
crop. This occurs at some sites in all countries.
2. Decreases in water availability. Depletion of soil water is increased by
greater evapotransipration and, in some cases, a decrease in precipitation in
the climate change scenarios. This occurred in Argentina, Brazil, Canada,
France, Japan, Mexico and USA.
3. Poor vernalization. Some temperate cereal crops require a period of low
temperature in winter to initiate the flowering process. Inadequate
vernalization results in low flower bud initiation and ultimately in reduced
yields. This caused decreases in yields in winter wheat yields in some sites in
Canada and the former USSR.
M. Parry and M. Livermore
116
adaptations at the farm level that would not involve any major changes in
agricultural practices. It thus took account of changes in planting date, amounts
of irrigation and the choice of crop varieties that are currently available.
Adaptation Level 2 encompassed, in addition to the former, major changes in
agricultural practices, such as large shifts of planting date, the availability of new
cultivars, extensive expansion of irrigation and increased fertilizer application.
This level of adaptation would be likely to involve policy changes both at the
national and international level and significant costs. However, policy, cost and
water were not studied explicitly.
Scenarios of different future trade, economic and population growth. A final set of
scenarios assumed changes to the world tariff structure and different rates of
growth of economy and population. As with previous experiments, these were
conducted both with and without climate change impacts. These scenarios included:
E Full trade liberalization. Full trade liberalization in agriculture introduced
gradually by 2020.
E Lower economic growth (ranging from 2.7% per year in 1980—2000 to 1.0%
in 2040—2060). Global GDP in 2060 is 10.3% lower than the reference
scenario, 11.2% lower in developing countries and 9.8% lower in developed
countries.
E Low population growth. UN low population estimates (ca. 8.6 billion by 2060).
Effects on Yields
The results show that climate change scenarios excluding the direct physiological
effects of CO
predict decreases in simulated yields in many cases, while the direct
effects of increasing atmospheric CO
mitigate the negative effects primarily in
mid- and high-latitudes. The differences between countries in yield responses to
climate change are related to differences in current growing conditions. At low
latitudes crops are grown nearer the limits of temperature tolerance and global
warming may subject them to higher stress. In many mid- and high-latitude areas,
increasing temperatures may benefit crops otherwise limited by cold temperatures
and short growing seasons in the present climate.
The primary causes of decreases in yield are:
1. Shortening of the growing period (especially the grain filling stage) of the
crop. This occurs at some sites in all countries.
2. Decreases in water availability. Depletion of soil water is increased by
greater evapotransipration and, in some cases, a decrease in precipitation in
the climate change scenarios. This occurred in Argentina, Brazil, Canada,
France, Japan, Mexico and USA.
3. Poor vernalization. Some temperate cereal crops require a period of low
temperature in winter to initiate the flowering process. Inadequate
vernalization results in low flower bud initiation and ultimately in reduced
yields. This caused decreases in yields in winter wheat yields in some sites in
Canada and the former USSR.
M. Parry and M. Livermore
116