TABLE 4.3 Median estimates of global impacts of temperature and precipitation trends, 1980-2008, on
average for four major crops
(million metric tons)
trend on yield
trend on yield
of CO 2 trends
Source : derived from Lobell et al ., 2011.
Estimates of the 47 ppm increase in CO 2 over the time period.
The positive impact of CO 2 fertilization offsets the impact of temperature and precipita-
tion in some crops, but not in others. It also has no effect on maize yields, which are particu-
larly sensitive to temperature increases. Lobell also creates maps of these changes, showing
where the effects of climate are strongest, which could lead to improved adaptation programs.
Given the rise in demand for rice and wheat, the reduction in yields due to climate change
may have a significant effect on the price of these foods and will impact farmers with a high
dependence on this crop.
Of course, climate is only one factor likely to shape the future state of the food supply.
Technology change during the period was also a significant driver, which could be identified
and disaggregated from climate trends. Lobell et al . (2011) divided the observed trends in
yields into those that were more related to climate and those that were not. The study showed
that environmental trends were able to set back yield gains due to technology for the equi-
valent of ten years, and had a widespread, spatially coherent impact on yields (Lobell et al .,
The impact of climate variability showed a wide variation across countries and regions. As
was also found in Simelton et al . (2012), lesser developed countries with a high proportion of
their GDP in the agriculture sector such as Russia, Turkey and Mexico were disproportion-
ately affected by climate variability. As food becomes more valuable, the incentive to invest
in agriculture will grow. For most of the twentieth century, food prices have remained level
or have declined slightly. Thus the impact of recent significant increases in commodities has
not yet been incorporated into these calculations.
Trends in per capita food availability
To explore the impact of changing rainfall, productive capacity and population, a simple food
balance model can be used. This analysis explores the impact of trends in each of these cat-
egories to understand how investments in productive capacity might reduce the impact of
climate variability. The underlying assumption of this work is that local food production and
availability is increasingly important for the food security of a region. Because some regions