New And Precise Environmental Article Summary

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Acknowledgments: We thank all members of the Moritz lab for their helpful comments and suggestions. C.M.’s research relating to climate change effects has been supported by the National Science Foundation (the Australian Research Council) and the Gordon and Betty Moore Foundation. R.A. is funded by a Spanish postdoctoral fellowship financed by the Ramon Areces Foundation (www.fundacionareces.es/ fundacionareces/).

10.1126/science.1237190

REVIEW

Climate Change Impacts on Global Food Security Tim Wheeler1,2* and Joachim von Braun3

Climate change could potentially interrupt progress toward a world without hunger. A robust and coherent global pattern is discernible of the impacts of climate change on crop productivity that could have consequences for food availability. The stability of whole food systems may be at risk under climate change because of short-term variability in supply. However, the potential impact is less clear at regional scales, but it is likely that climate variability and change will exacerbate food insecurity in areas currently vulnerable to hunger and undernutrition. Likewise, it can be anticipated that food access and utilization will be affected indirectly via collateral effects on household and individual incomes, and food utilization could be impaired by loss of access to drinking water and damage to health. The evidence supports the need for considerable investment in adaptation and mitigation actions toward a “climate-smart food system” that is more resilient to climate change influences on food security.

Tackling hunger is one of the greatest chal-lenges of our time (1). Hunger has multi-ple dimensions and causes, ranging from deficiencies in macro- and micro-nutrients, throughshort-term shocks on food access, to chronic short-ages. Causes range from constraints on the supply

of food of sufficient quantity and quality and lack of purchasing power to complex interactions of nutrition with sanitation and infectious diseases leading to poor health. Several of these causes have been addressed in recent decades, and sub- stantial progress has been made in reducing the proportion of the world’s undernourished popu- lation from an estimated 980 million in 1990–92 to about 850 million in 2010–12 (2). However, from other relevant indicators of nutrition, such as child underweight and stunting and health sur- veys, an estimated 2 billion people still suffer from micro-nutrient deficiencies today.

The long-term reduction in the prevalence of undernutrition worldwide has slowed since 2007, as a result of pressures on food prices, economic

1Walker Institute for Climate System Research, Department of Agriculture, University of Reading, Reading RG6 6AR, UK. 2Department for International Development, 22-26 Whitehall, London SW1A 2EG, UK. 3ZEF B: Center for Development Re- search, Department of Economic and Technical Change, Univer- sity of Bonn, Walter-Flex-Strasse 3 53113 Bonn, Germany.

*Corresponding author. E-mail: t.r.wheeler@reading.ac.uk

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volatilities, extreme climatic events, and changes in diet, among other factors. Furthermore, addi- tional pressures on the global food system are expected to build in the future. For example, de- mand for agricultural products is estimated to increase by about 50% by 2030 as the global pop- ulation increases (3), which will require a shift toward sustainable intensification of food systems (4). The impacts of climate change will have many effects on the global food equation, both for sup- ply and demand, and on food systems at local levels where small farm communities often depend on local and their own production (5). Thus, cli- mate change could potentially slow down or re- verse progress toward a world without hunger.

Here, we offer an overview of the evidence for how climate change could affect global food sec- urity, with particular emphasis on the poorer parts of the world. We deliberately take a broad view of the complex interactions between climate change and global food security, stating what we do know with some degree of confidence, as well as ac- knowledging aspects where there is little or no evi- dence. We end by proposing a number of precepts for those making policy or practical decisions on climate change impacts and food security.

Food Security Together, climate change and food security have multiple interrelated risks and uncertainties for societies and ecologies. The complexity of global

food security is illustrated by the United Nations’ Food and Agricultural Organization (FAO) (6) definition: (i) the availability of sufficient quantities of food of appropriate quality, supplied through domestic production or imports; (ii) access by in- dividuals to adequate resources (entitlements) for acquiring appropriate foods for a nutritious diet; (iii) utilization of food through adequate diet, clean water, sanitation, and health care to reach a state of nutritional well-being where all physio- logical needs are met; and (iv) stability, because to be food secure, a population, household or in- dividual must have access to adequate food at all times.

It is extremely challenging to assess precise- ly the current status of global food security from such a broad concept. However, the big picture is clear: About 2 billion of the global population of over 7 billion are food insecure because they fall short of one or several of FAO’s dimensions of food security. Enormous geographic differ- ences in the prevalence of hunger exist within this global estimate, with almost all countries in the most extreme “alarming” category situated in sub-Saharan Africa or South Asia (7) (Fig. 1).

Nevertheless, it is important to note that the current numbers for undernourished people are rough estimates at best and are seriously defi- cient in capturing the access, utilization, and stability dimensions of food security. First, the methods used to make these estimates only cap-

ture longer-term trends, not the short-term changes that can be an important consequence of climate variability. The most recent data are averages for the period 2010–2012 (2), so they do not cap- ture a specific year, let alone shorter-term shocks, be they climate-related or otherwise. Second, they estimate calorie shortage only and do not cover other dietary deficiencies and related health ef- fects that can impair physical and mental capac- ities. Third, they are derived from aggregate data, not actual household or individual-level food de- ficiencies, which hinders analyses of distribu- tional effects of climate and other shocks. The FAO methodology was recently improved (8), but the above shortcomings could not be addressed within the framework of the current method, and thus, current analyses of climate change impacts on food security are incomplete. An overhaul of data-gathering methods that encompasses food deficiencies at household levels, as well as nu- tritional status, is needed.

Climate Change There is a substantial body of evidence that shows that Earth has warmed since the middle of the 19th century (9–14). Global mean tem- perature has risen by 0.8°C since the 1850s, with the warming trend seen in three independent tem- perature records taken over land and seas and in ocean surface water (15). Climate change can result from natural causes, from human activities

Fig. 1. Global distribution of hunger as quantified by the 2012 Global Hunger Index. TheWelthungerhilfe, IFPRI, andConcernWorldwideHungermap2012 calculated a Global Hunger Index (7) for 120 countries by using the proportion of

people who are undernourished, the proportion of children under 5 who are under- weight, and the mortality rate of children younger than age 5, weighted equally. [Reproduced with permission fromWelthungerhilfe, IFPRI, and ConcernWorldwide (7)]

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