Carbon dioxide emissions from fossil-fuel burning and industrial processes have accelerated on the global scale over the past two decades (Canadell et al. 2007; Raupach et al. 2007). The growth rate of global atmospheric CO2 for 2000-2006 was 1.93 ppm per year, which is the highest rate since the beginning of continuous

USDA ARS Photosynthesis Research Unit; Department of Plant Biology, University of Illinois, Urbana-Champaign, 147 Edward R. Madigan Laboratory, 1201 W. Gregory Drive, Urbana, IL 61801, USA

email: [email protected] J.M. McGrath

USDA ARS Photosynthesis Research Unit

D. Lobell and M. Burke (eds.), Climate Change and Food Security, Advances in Global Change Research 37, DOI 10.1007/978-90-481-2953-9_7, © Springer Science + Business Media, B.V. 2010

monitoring in 1959. The current atmospheric CO2 concentration ([CO2]) of 385 ppm in 2008 ( is higher than it has been in the past 650,000 years (Siegenthaler et al. 2005), and the concentration will continue to rise in the coming century. Atmospheric [CO2] will likely reach 550 ppm by 2050 and 730-1020 ppm by 2100 (Meehl et al. 2007). Crops are therefore currently exposed to a [CO2] that has not been experienced since the early Miocene, and agriculture is facing a future of uncertain consequences of global climate change.

Elevated [CO2] directly stimulates photosynthesis in C3 crops (e.g., wheat, rice and soybean), leading to increases in crop growth and seed yield (Kimball et al. 2002; Long et al. 2004; Nowak et al. 2004; Ainsworth and Long 2005). Elevated [CO2] also directly decreases the conductance of CO2 and water vapor through stomata, the pores in the leaf epidermis, of both C3 and C4 crops (e.g., maize, sorghum and sugarcane), which can improve water-use efficiency and therefore benefit all crop production in times and places of drought (Kimball et al. 2002; Ottman et al. 2001; Leakey et al. 2004, 2006; Leakey 2009). While rising [CO2] is just one factor of global climate change, it plays a direct role in the sustainability of the future world food supply and projections of people at risk of hunger (Parry et al. 2004). Furthermore, the changes in temperature, precipitation and tropospheric ozone concentration projected for this century are spatially and temporally variable, while the increase in [CO2] is uniform, global and committed (Solomon et al. 2007). Therefore, understanding crop responses to [CO2] is a critical first step in adapting agriculture to anticipated global change.

In this chapter, we review the experimental approaches that have been used to investigate crop responses to rising atmospheric [CO2], summarize the current understanding of how rising atmospheric [CO2] will alter crop physiology and yield, discuss how models extrapolate this information beyond experimental settings to make predictions of food production and security in the future, discuss potential effects of elevated ozone, and identify major knowledge gaps and challenges for future research.

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