Crop-yield variability

Sensitivity of cereal yields to climate change for maize and wheat

Note: A small increase in temperature has a positive impact on cereals yield, while a high increase (3-5 oC) has a negative impact

Data source:

Easterling, W. E.; Aggarwal, P. K.; Batima, P.; Brander, K. M.; Erda, L.; Howden, S. M.; Kirilenko, A.; Morton, J.; Soussana, J.-F.; Schmidhuber, J. and Tubiello, F. N., 2007. Food, fibre and forest products. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Parry, M. L.; Canziani, O.F.; Palutikof, J. P.; van der Linden, P. J. and Hanson, C. E. (eds.), Cambridge University Press, Cambridge, UK, 273-313.

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Past trends

While the area under arable cultivation in most of western Europe has decreased over the past 40 years, crop yields have increased almost continuously (Eurostat). This trend has persisted into the 21st century, although crop-yield variability increased as a consequence of several extreme meteorological events in short succession: a late frost in 2003 followed by a severe drought reduced cereal yields over most of Europe, a drought in 2005 severely affected western Europe (Iberian Peninsula), and an early drought in 2006 was followed by extreme rains during the summer, resulting in lower cereal production, especially in eastern Europe (EC, MARS Bulletins, 2008). Alexander et al. (2006) found a general increase in the intensity of precipitation events observed at the global level. For the Mediterranean area, where climate vulnerability is high, several studies found an increasing trend towards more intense precipitation and a decrease in total precipitation (Alpert et al., 2002; Maheras et al., 2004; Brunetti et al., 2004). In general, it is difficult to separate the climate effects from those of improved agricultural techniques in the development of historic crop yields. Adaptive management is expected to continue to help reduce the risks to agricultural yields from climate change, and to make better use of opportunities.

Projections

The effects on agricultural yields of increasing mean daily temperatures depend on their magnitude and geographic extent. The production areas of some crops could expand northwards in Europe, e.g. for maize. With an increase in mean annual temperature of 2 ^oC, cereal yields are expected to increase, partly because of the fertilisation effect of the increase in CO₂ (Parry et al., 2004). However, an increase of 4 ^oC or more will shorten the crop cycle and the CO₂ effect will not compensate for the resulting loss of yield. Crop yields are also at risk from more intensive precipitation and prolonged periods of drought, particularly in areas bordering the Mediterranean basin. Figure 1 shows the sensitivity of maize and wheat yields to climate change, as derived from the results of 69 published studies. These span a range of precipitation changes and CO₂ concentrations, and vary in how they represent future changes in climate variability. Responses include cases without adaptation (red dots) and with adaptation (dark green dots). Adaptation represented in these studies includes changes in planting dates and crop varieties, and shifts from rain-fed to irrigated conditions.