Page 128 - Climate Change and Food Systems

climate change and food systems: global assessments and implications for food security and trade
1. Introduction
1.1 Background and objectives
This paper deals primarily with the biophysical assessment of climate change (CC) impacts on agricultural potential and crop yields. Bio-economic impact assessment approaches for agriculture (e.g. Nelson et al., 2009; 2014) are dealt with in detail elsewhere (see other chapters in this volume).
This paper focuses on recent assessments
of major European food crops and commodities. Most of the studies examined are based on climate projections generated by global and regional climate models which have been downscaled and fed into process-based crop simulation models (e.g. Supit et al., 2012; Angulo et al., 2013;
Asseng et al., 2013; Rosenzweig et al., 2013).
We also include results from other biophysical impact assessment studies using methods such as statistical crop yield models (e.g. Schlenker and Lobell, 2010) or agroclimatic indicator approaches (Trnka et al., 2011; Rötter et al., 2013a). Regional differences with regard to expected climate changes and their impacts on shifts in crop suitability and yields are highlighted and discussed.
Observed weather data indicate that global warming is causing changes in rainfall patterns and increasing the frequency and severity of extreme events such as heat waves and drought (Trenberth, 2011; Schiermeier, 2011; Coumou
and Rahmstorf, 2012; Field et al., 2012; WMO, 2013). Such changes are also projected by climate models for future conditions (Meehl et al., 2007; Rummukainen 2012, 2014; Sloth Madsen et al., 2012). As of yet, there is no clear or well- established understanding of the relationship between global warming and enhanced climatic variability (see Rummukainen, 2014). However, increased climatic variability, as well as more frequent extreme weather events – particularly their impacts on crop yields and production (Schlenker and Lobell, 2010; Hatfield et al., 2011) – would increase risks to food production (Rötter et al.,
2012a, 2013a; Williams, 2012) and farm income (Wheeler and von Braun, 2013).
Therefore, we pay special attention to the capability and limitations of current biophysical assessment approaches and modelling tools for capturing impacts of variability and extremes of weather on crop yields (Rötter et al., 2011a), and report on recent progress in this respect (e.g. Challinor et al., 2005; Rötter et al., 2011b; Asseng et al., 2011; Tao and Zhang, 2013; Sanchez et al., 2014).
Following a brief overview of how crop simulation models – the most widely used biophysical assessment tools (e.g. White et al., 2011) – are commonly applied in CC impact assessments, we present a range of selected CC impacts for key crops and regions, with a focus
on the European Union (EU-27). Beginning with production trends of the past, we move to shifts
in future production possibilities and relative crop yield changes under alternative projections of future climate, and conclude this overview for Europe with expected shifts in future crop production potentials and implications for global trade and food security.
The presentation of selected key impacts
is followed by a detailed discussion of various uncertainties. These are not restricted to uncertainties related to biophysical models, but also include other sources of uncertainty, such
as that originating from climate models, from downscaling or regionalizing climate model outputs and from several of the other “unknowns” regarding technology development and other socio-economic factors (Rötter et al., 2012a; 2013b). We conclude with suggestions for improvement of biophysical assessment methodology and modelling tools (see green box at centre of Figure 1a).
Specific objectives of this chapter are as follows:
1. To present current biophysical assessment methodology and discuss its shortcomings and recent developments;
2. To present recent results from different studies of CC impacts on key crops – for Europe as a whole and for its various subregions;
108