Virtual Special Issue on food security – greater than anticipated impacts of near‐term global atmospheric change on rice and wheat

Working Group II (WGII) of the Intergovernmental Panel on Climate Change (IPCC), concluded in their fourth assessment report (AR4) that despite climate change and increasing world population, crop surpluses at the global level would continue, resulting in a ‘small decline in real world food (cereal) prices’ over this century (www.ipcc.ch/publications_and_data/ publications_and_data_reports.shtml). In 2009, Assistant Director-General Hafez Ghanem of the UN Food and Agriculture Organization (FAO) stated ‘FAO is cautiously optimistic about the world’s potential to feed itself by 2050’ (www.fao.org/news/story/en/item/ 35571/icode/). This is despite the fact that with increasing affluence and a third more people it was estimated that 70% more food would be needed by 2009. Underpinning this optimism is the fact that yields have increased steadily at around 1.5–2% p.a. for almost 60 years, and that this might be expected to continue, or even accelerate in response to increased prices (IPCC AR4). While it has to be hoped that this optimism is realized, the year-on-year increases achieved with the two most important food crops to the world ceased for wheat and slowed for rice in the first years of this Century (Fig. 1). Further, research subsequent to the IPCC assessment shows aspects of global atmospheric change anticipated for mid-century that will drive down yields. This research is consolidated in this Virtual Special Issue of Global Change Biology comprising 11 articles that focus on post AR4 assessments of the response of rice and of wheat to rising carbon dioxide, tropospheric ozone and temperature (Ainsworth, 2008; Biswas et al., 2008; Feng et al., 2008, 2011; Shimono et al., 2008; Taub et al., 2008; Liu et al., 2010; Asseng et al., 2011; Wall et al., 2011; Zhu et al., 2011; Pleijel & Uddling, 2012). Atmospheric [CO2] is expected to rise to about 550 ppm by mid-century. In theory this would be sufficient to increase yield by almost 30%. Ainsworth (2008) conducted a meta-analysis of studies of the impacts of rising [CO2] and of tropospheric [O3] on rice. This work showed that while yield increases approaching 30%, and of the scale anticipated by IPCC WGII, were seen in some studies in which [CO2] was elevated in artificial enclosed environments, ‘the more closely the fumigation mimicked field conditions, the smaller was the stimulation of yield by elevated [CO2]. ’ The average increase in yield under Free Air Concentration Enrichment (FACE) of [CO2], where elevation is under entirely open-air field conditions, was just 12%. Indeed, results from the large-scale FACE experiment in Japan, in which [CO2] was elevated to ca. 580 ppm, showed that rice yield was increased on average by just 11.5% (Shimono et al., 2008). Across the studies surveyed by Ainsworth (2008), combining elevated temperature with the elevation of [CO2] negated any increase in rice yield. In a separate meta-analysis, growth under elevated [CO2] was found to decrease the grain protein content of both rice and wheat by ca. 10% (Taub et al., 2008). Pleijel & Uddling (2012) confirm this effect in an extensive meta-analysis of the impact of elevated [CO2] and [O3] on wheat, incorporating 57 experiments which cover 24 cultivars and 112 independent experimental treatments. Here, too yield increase by elevated [CO2] in wheat was negatively correlated with protein content of the grain. Pre-industrial concentrations of ozone in the troposphere ([O3]) were less than 10 ppb. Today, levels in much of the northern hemisphere are 40–60 ppb, with higher levels in E. and S. Asia, and may increase another 20–80% by mid-century according to the IPCC AR4 Working Group I. Tropospheric O3 is a secondary pollutant resulting from the interaction of sunlight, gaseous