Adaptation to Climate Change in the Agricultural Sector
AEA Energy & Environment, 2007
Implications for EU agriculture
- Factors that increase yields: higher atmospheric CO2 concentration.
- Factors that decrease yields: higher atmospheric Ozone concentration (entering plant leaves and reducing the efficiency of photosynthesis), sea levels rise, intensified hydrological cycle (e.g. more winter precipitation is projected to fall as rain, rather than snow, decreasing snow pack and spring runoff, potentially exacerbating spring and summer droughts) and extreme weather events.
- Ambiguous factors: higher temperatures (High latitudes and high elevations are likely to experience greater warming than the global mean, especially in winter) and changing temperature patterns (winter and nocturnal temperatures are projected to rise disproportionately).
- The forecasted changes in yield vary greatly across the EU (depending on local climate, water availability, soils etc). Relatively northern zones (Boreal, Atlantic Central, and Continental North) fare better than southern zones. Yield increases up to 40% in Scandinavia’s boreal areas, yield decreases up to 40% in the Mediterranean region under current management conditions.
- For crop production, a change in the seasonality of precipitation may be even more important than a change in the annual total. The water regime of crops is vulnerable to a rise in the rate and seasonal
pattern of evapotranspiration, brought on by warmer temperatures, drier air, or windier conditions. Crop yields are most likely to suffer if dry periods occur during critical developmental stages. In most
grain crops, flowering, pollination, and grain-filling are especially sensitive to water stress.
- In some regions a positive relationship between temperature and crop yield is forecast with increased wheat and grass yields resulting from higher temperatures and increased CO2 concentrations.
Greater concentrations of CO2 in the atmosphere have the potential to increase biomass production and to increase the physiological efficiency of water use in crops and weeds. However, increases in CO2 do not produce proportional increases in crop productivity; other factors play a significant role. While experiments with increased concentrations of CO2 under controlled conditions have been shown to significantly increase yields of crops, these increases have occurred when other factors such as moisture supply, nutrients and pest and disease incidence have not been limiting. In practice, an insufficient supply of water or nutrients or greater pest/disease attack or competition from weeds is expected to frequently negate the fertilizing impact of increased CO2 concentrations in the atmosphere. Since weed growth may also be enhanced by increased CO2, a changed weed ecology may emerge with the potential to increase weed competition with crops.
- Heat stress and drought stress often occur simultaneously, with one contributing to the other. They are often accompanied by high solar irradiance and high winds. When crops are subjected to drought stress, their stomata close. Such closure reduces transpiration and, consequently, raises plant temperatures.
- An indirect effect on agriculture may occur if rising sea levels make population centres uninhabitable. The displaced populations will need to be housed and at least some of the housing is likely to be built on agricultural land.
- Agro-forestry, by providing shade, has the potential to counteract the effects of increased summer temperatures on current crops and livestock by moderating microclimates. Shelter given by trees and shade in summer has been shown to improve yields of nearby crops and, reducing heat stress, can be beneficial for livestock. These benefits occur because of modifications to the micro-environment which reduce crop evapotranspiration and conserve soil moisture. For example, in the east of Scotland, pasture production below well-grown agro-forestry trees has been found to be up to 16% greater than conventional pastoral agriculture