Recent research strongly suggests that rising temperatures and accompanying changes in precipitation have already had observable effects on agriculture.
remained relatively flat for the past 30 years, with a large dip in 2008 as the global economic crisis reduced economic activity. Emissions from con- sumption have continued to grow in the form of emissions associated with imports produced in devel- oping countries. In stark contrast, developing-country emissions
have grown dramatically, surpassing those from developed countries by the late 2000s. Te green shaded area indicates that a significant and growing portion of developing-country emissions are from production for export to developed countries, but emissions from domestic consumption have sur- passed those from developed-country consumption. Tis situation makes it increasingly obvious that developing countries should not be excluded from national commitments to reduce emissions, as they
FIGURE 2 Change in growing season temperature, 1980–2008
20 40 60
−40 −20 0
−100 −50 0 50 100 150
Source: Figure 1 in D. B. Lobell, W. Schlenker, and J. Costa-Roberts, “Climate Trends and Global Crop Production since 1980,” Science 333, no. 6042 (2011): 616–620, doi:10.1126/science.1204531.
44 MODEST ADVANCES, STARK NEW EVIDENCE
were in the Kyoto Protocol. As incomes in devel- oping countries grow, they must pursue low-emis- sions development strategies. Climate scientists are increasingly confident
of the link between recent anthropogenic emis- sions of greenhouse gases and rising temperatures such as those experienced in Iowa, in the heart of the US Corn Belt. Researchers have demon- strated the threat to US maize production from higher temperatures based on a detailed statisti- cal analysis of actual maize yields from 1950 to 2005.6 Teir findings show that as average growing season temperatures rise to 28°C, yields are rela- tively litle affected. However, once temperatures surpass the threshold of about 30°C, yields drop precipitously. Another study using extensive maize experimental data from International Maize and Wheat Improvement Center trials in Sub-Saharan Africa had broadly similar results.7 Under optimal management, when the mean growing season tem- perature is less than 22°C, a 1°C increase in tem- perature has a small but positive effect on yields. But as the average growing season temperature exceeds 25°C, the effect becomes negative, causing roughly a 30 percent decline in yields. And during
−3 −2 −1 0 1 2 3
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