Geoscience Reference
In-Depth Information
thermal inputs, while the same increase of temperature will
have a greater relative effect at higher latitudes than at lower
latitudes due to greater temperature increases at higher latitudes
(Parry et al., 1990). Considering the examples of the adjustment
and yield increase of wheat in India, maize in Iowa, United
States and northern Europe, rice in Philippines and Indonesia,
soya bean in Brazil, sunflower in the Red Valley of the United
States, oil palm in Malaysia and canola (rape) in Canada, the
future adjustment of agricultural crop production can also be
indexed by an already observed rate of change (Wittwer, 1990).
Global warming projection, especially during winter months at
high latitudes (Williams and Oakes, 1978; Parry et al., 1988,
1989; Wittwer, 1990), will extend the efficient crop ecological
zone indicating a significant northward shift of balance of agri-
cultural resources (Parry et al., 1989).
The extent of this crop ecological zone may not make the
introduction of new genetic material necessary as it would
advance the thermal limit of cereal cropping in mid-latitude
Northern Hemisphere regions by about 150-200 km and raise
the altitudinal limit by about 150-200 m in the European Alps,
making it similar to the Pyrenees located 300 km south of the
Alps (Parry et al., 1989). A rise of temperature in cool temper-
ate and cold regions will lengthen the potential growing sea-
son and increase growth rates. This will shorten the required
growing period (except where moisture is a limiting factor),
as in Finland where yields of barley and oat will increase by
9-18% (Kethunen et al., 1988), in Iceland where the carrying
capacity of grasslands for sheep will increase by two and half
times (Bergthorsson et al., 1988) and critically low-yield steppe
regions will have a twofold increase in yields (Sirotenko et al.,
1997). In areas presently with low precipitation, the elevated
CO
2
concentration will be beneficial to the crop yields as in
China during summer monsoon where an increase in 100 mm
rainfall with 1°C temperature rise will increase yields of rice,
maize and wheat by 10% (Zhang, 1989) and similarly in Japan
(Yoshino et al., 1988). The projected climate change due to an
increase in CO
2
concentration will favour a change from the
existing, often quick maturing cultivars to be grown for a lon-
ger and more intense growing season and late maturing variet-
ies will be more suitable for such conditions. For instance, late
growing rice cultivars presently in Central Japan will have a
yield increase of 26% and quick maturing varieties now grow-
ing in northern Japan will have increase of only 4% (Yoshino
et al., 1988). Similarly, a switch to winter-sown cereals (wheat,
barley and oats), as in the case of wheat in Saskatchewan and
