IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability

12.4.7 Agriculture and fisheries Crops and livestock

The effects of climate change and increased atmospheric CO2 are expected to lead to overall small increases in European crop productivity. However, technological development (e.g., new crop varieties and better cropping practices) might far outweigh the effects of climate change (Ewert et al., 2005). Combined yield increases of wheat by 2050 could range from 37% under the B2 scenario to 101% under the A1 scenario (Ewert et al., 2005). Increasing crop yield and decreasing or stabilising food and fibre demand could lead to a decrease in total agricultural land area in Europe (Rounsevell et al., 2005). Climate-related increases in crop yields are expected mainly in northern Europe, e.g., wheat: +2 to +9% by 2020, +8 to +25% by 2050, +10 to +30% by 2080 (Alexandrov et al., 2002; Ewert et al., 2005; Audsley et al., 2006; Olesen et al., 2007), and sugar beet +14 to +20% until the 2050s in England and Wales (Richter and Semenov, 2005), while the largest reductions of all crops are expected in the Mediterranean, the south-west Balkans and in the south of European Russia (Olesen and Bindi, 2002; Alcamo et al., 2005; Maracchi et al., 2005). In southern Europe, general decreases in yield (e.g., legumes -30 to + 5%; sunflower -12 to +3% and tuber crops -14 to +7% by 2050) and increases in water demand (e.g., for maize +2 to +4% and potato +6 to +10% by 2050) are expected for spring sown crops (Giannokopoulos et al., 2005; Audsley et al., 2006). The impacts on autumn sown crops are more geographically variable; yield is expected to strongly decrease in most southern areas, and increase in northern or cooler areas (e.g., wheat: +3 to +4% by 2020, -8 to +22% by 2050, -15 to +32% by 2080) (Santos et al., 2002; Giannakopoulos et al., 2005; Audsley et al., 2006; Olesen et al., 2007).

Some crops that currently grow mostly in southern Europe (e.g., maize, sunflower and soybeans) will become viable further north or at higher-altitude areas in the south (Audsley et al., 2006). Projections for a range of SRES scenarios show a 30 to 50% increase in the area suitable for grain maize production in Europe by the end of the 21st century, including Ireland, Scotland, southern Sweden and Finland (Hildén et al., 2005; Olesen et al., 2007). By 2050 energy crops (e.g, oilseeds such as rape oilseed and sunflower), starch crops (e.g., potatoes), cereals (e.g., barley) and solid biofuel crops (such as sorghum and Miscanthus) show a northward expansion in potential cropping area, but a reduction in southern Europe (Tuck et al., 2006). The predicted increase in extreme weather events, e.g., spells of high temperature and droughts (Meehl and Tebaldi, 2004; Schär et al., 2004; Beniston et al., 2007), is expected to increase yield variability (Jones et al., 2003) and to reduce average yield (Trnka et al., 2004). In particular, in the European Mediterranean region, increases in the frequency of extreme climate events during specific crop development stages (e.g., heat stress during flowering period, rainy days during sowing time), together with higher rainfall intensity and longer dry spells, are likely to reduce the yield of summer crops (e.g., sunflower). Climate change will modify other processes on agricultural land. Projections made for winter wheat showed that climate change beyond 2070 may lead to a decrease in nitrate leaching from agricultural land over large parts of eastern Europe and some smaller areas in Spain, and an increase in the UK and in other parts of Europe (Olesen et al., 2007).

An increase in the frequency of severe heat stress in Britain is expected to enhance the risk of mortality of pigs and broiler chickens grown in intensive livestock systems (Turnpenny et al., 2001). Increased frequency of droughts along the Atlantic coast (e.g., Ireland) may reduce the productivity of forage crops such that they are no longer sufficient for livestock at current stocking rates without irrigation (Holden and Brereton, 2002, 2003; Holden et al., 2003). Increasing temperatures may also increase the risk of livestock diseases by (i) supporting the dispersal of insects, e.g., Culicoides imicola, that are main vectors of several arboviruses, e.g., bluetongue (BT) and African horse sickness (AHS); (ii) enhancing the survival of viruses from one year to the next; (iii) improving conditions for new insect vectors that are now limited by colder temperatures (Wittmann and Baylis, 2000; Mellor and Wittmann, 2002; Colebrook and Wall, 2004; Gould et al., 2006).