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but above this range (after 2050) may decrease (IPCC, 2007;
Meehl
et al
., 2007). Model projections suggest that although
increased temperature and decreased soil moisture will act to
reduce global crop yields by 2050, the direct fertilization ef-
fect of rising carbon dioxide concentration (CO
2
) will offset
these losses. The CO
2
fertilization factors used in models to
project future yields were derived from enclosure studies con-
ducted about 20 years ago. Free-air concentration enrichment
(FACE) technology has now facilitated large-scale trials of the
major grain crops at elevated CO
2
levels under full open-air
field conditions. In those trials, elevated CO
2
enhanced yield
by about 50% less than in the enclosure studies. Hence, previ-
ous projections of no impact or even a slight positive impact
of increasing CO
2
on global agricultural production by 2030
and 2050 may be too optimistic (Long
et al
., 2006). Current
research results conclude that while crops would respond posi-
tively to elevated CO
2
in the absence of climate change, the as-
sociated impacts of high temperatures, altered patterns of pre-
cipitation, and possible increased frequency of extreme events
such as droughts and floods, will likely combine to depress
yields and increase production risks in many world regions
(Tubiello and Fischer, 2006).
Furthermore, projected changes in the frequency and sever-
ity of extreme climate events are predicted to have more seri-
ous consequences for food and food security than changes in
projected mean temperatures and precipitation (IPCC, 2007).
Also, regional differences will grow stronger with time (Parry
et al
., 2005), with potentially large negative impacts in develop-
ing regions but only small changes in developed regions (IPCC
2007; Slater
et al
. 2007). Developing countries are more vul-
nerable because of the dominance of agriculture in their econ-