The Food and Agriculture Organization of the United Nations (FAO 2008) describes four dimensions of food security: availability, related to quantity; access, including affordability; utilization, related to meeting nutritional needs and food safety; and stability, related to the temporal variation in the other dimensions.
Availability: Current levels of ground-level O3 decrease yields of key staple crops – including wheat, soybean, maize and rice – by 2-15 per cent depending on crop types and locations (Feng and Kobayashi 2009; Van Dingenen et al. 2009; Fishman et al. 2010; Avnery et al. 2011). Global estimates of damage are uncertain because different cultivars of crops have different sensitivities and not all crops have been studied. The economic implications of loss of crop productivity are substantial. For example, elevated O3 concentrations in the United States of America reduce maize and soybean production by about 10 per cent and 5 per cent, respectively, at a cost of US$9 billion annually (McGrath et al. 2015).
Climate change already affects crop production through changes in average and extreme temperatures and precipitation, the spread and impacts of invasive weeds and pests and deforestation. Although increased CO2 fertilization (see Section 4.4.3) is thought to offset negative impacts, the interactions between changes in CO2, O3, nitrogen, water availability and temperature are still not well understood (Schlenker and Roberts 2009; Porter et al. 2014).
Yields in tropical countries are expected to suffer the most serious impacts, while some temperate regions may benefit from higher yields, expansion of productive areas and longer growing seasons (though these benefits may be offset by increasingly frequent extreme events, temperature and water stresses and ineffective adaptations) (Schmidhuber and Tubiello 2007; Gornall et al. 2010; Porter et al. 2014). In short, the impact of climate change on crop production will be felt most heavily in developing countries where large numbers of people depend on agriculture for their livelihoods, food insecurity is high and adaptive capacity low. Climate change impacts on the availability and distribution of aquatic species are also expected to disproportionately affect developing countries (see Section 7.3.2).
Higher temperatures are likely to adversely affect livestock productivity by changing the availability of pasture, fodder crops and water (Andre et al. 2011; Renaudeau et al. 2011; Porter et al. 2014). The impacts of climate change on livestock diseases remain difficult to predict and highly uncertain (Mills, Gage and Khan 2010; Tabachnick 2010).
Access: Climate change exerts upward pressure on global food prices (Porter et al. 2014), disproportionately affecting poor consumers who may spend a significant proportion of their income on food, with implications for health and nutrition (Springmann et al. 2016). Women and girls disproportionately suffer from both the health consequences of nutritional deficiencies and the greater burdens of caregiving for others who are ill (WHO 2014; FAO 2016).
Utilization: Higher temperatures and higher CO2 levels are associated with lower protein content of grains (Porter et al. 2014; Feng et al. 2015) and reduced micronutrient content of grains and legumes (Myers et al. 2014).
The nutritional content and safety of food supply is affected by pollution, primarily by PBTs, including Hg and POPs. Hg can travel long distances in the air and water, bioaccumulate and biomagnify up food chains, reaching levels that can be dangerous to the health of ecosystems and humans (Gibb and O’Leary 2014; Sundseth et al. 2017). Concentrations of methylmercury in the blood of populations that consume top marine predators, such as indigenous Arctic people, are among the highest recorded globally, giving rise to serious health concerns (UNEP 2013a; UNEP 2013b). Hg is toxic to the central nervous system (CNS) leading to cognitive and motor dysfunction (Karagas et al. 2012; Antunes dos Santos et al. 2016; Sundseth et al. 2017). Hg exposure also increases the risk of cardiovascular diseases, causes kidney damage, adversely affects the reproductive, endocrine and immune systems, and leads to premature death (Rae and Graham 2004; AMAP 2009; Rice et al. 2014).
Similarly, POPs and other PBTs can travel long distances and bioaccumulate up food chains (e.g. Gibson et al. 2016; Ma, Hung, and Macdonald 2016). A wide range of health effects has been associated with exposure to POPs, including changes to the reproductive, endocrine, immunologic and neurologic systems, cancer, dermal and ocular changes, and reduced birth weight (Damstra 2002; El-Shahawi et al. 2010; Fry and Power 2017). The exposure of pregnant and breastfeeding women to POPs is of particular concern, as POPs can cross the placenta and the blood-milk barrier, which may increase the risk of adverse developmental outcomes in children (Vizcaino et al. 2014; Women in Europe for a Common Future and Women International for a Common Future 2016).
Little is known about the potential health effects of some chemicals that have substituted for banned POPs, such as non-polybrominated diphenyl ether (PBDE) organophosphate flame retardants. Human exposure to such flame retardants in the United States of America has been observed to be increasing over the last decade (Hoffman et al. 2017).
Stability: The increasing frequency and severity of extreme weather caused by climate change will have serious consequences for the stability of food prices and food supply, such as the wheat harvest failure and price spike experienced following the 2010 Russian heat wave (Otto et al. 2012; Porter et al. 2014). Droughts, floods and other weather-related disasters can lead to acute, localized food crises, particularly in countries with pre-existing vulnerabilities such as high levels of poverty and undernutrition. For example, climate change contributed to the drought that led to the 2011 East African food crisis and ultimately contributed to famine in Somalia (Bailey 2013; Lott, Christidis and Stott 2013; Coghlan et al. 2014). If transport infrastructure supporting exports from major crop-producing regions is disrupted by acute weather shocks, the impacts on food security could be more widespread (Bailey and Wellesley 2017).