2.3 Climate change and agriculture

Climate change will affect agriculture through effects on crops and weeds, soils, insects and disease. In terms of crops, the main climatic variables that are important are temperature, solar radiation, water and atmospheric CO2 concentration. However, whilst plant development is generally increased by temperature, CO2 enrichment can accelerate it even further in some cases, whilst in other cases it may have no effect or retarding effects in other cases.

Plant growth and crop yields depend on temperature and temperature extremes. The optimum range for C3 crops is 15–20°C and for C4 crops it is 25–30°C. The variation in temperature requirements and temperature extremes of different cultivars of the same species, and among species, is quite wide for most crops. C3 plants are sensitive to higher CO2 and typically respond with an increase in photosynthesis and growth, whilst C4 plants don't respond so dramatically. Typically, field-grown crops, such as winter wheat, carrot, cauliflower and onion, have been shown to increase leaf area and biomass during early crop growth under elevated CO2 conditions compared with ambient conditions.

Water stress has often been observed to be ameliorated by increasing concentrations of CO2. By inducing the partial closure of stomata, water is conserved. A study of plant responses to atmospheric CO2 enrichments under conditions of environmental stress concluded that the relative growth-enhancing effects of elevated CO2 were greatest when resource limitations and environmental stress were most severe.

Web-based resources on plant growth and CO2:

  • BBC Weather Centre on extreme weather on agriculture

  • Center for the Study of Carbon Dioxide and Global Change web page on ‘Interaction of CO2 and light on plant growth – summary’

  • Friends of Science website on CO2 and plant growth

  • Science Daily article ‘High carbon dioxide boosts plant respiration, potentially affecting climate and crops’.

3 The effects on yield and phenology