6.4.1 Climate change is expected to undermine crop yields.
Climate change is expected to undermine future crop yields , both in the short and long term
Porter, et al. (2014)
Regional variability is considerable, though it is expected that negative impacts on average yields will become likely from the 2030s.
Negative impacts of more than 5% are more likely than not beyond 2050 and likely by the end of the century. From the 2080s onwards, negative yield impacts in the tropics are very likely, regardless of adaptation or emission scenario.
Studies included in the IPCC reports have used models to identify South Asia and southern Africa as two regions where, without adaptation, there would be very negative impacts on several important crops.
Shorter-term impacts on crop yields are significant because of a projected increase in demand for food in the next 20 years
Graphs produced by FCRN from data in Lobell and Tebaldi (2014)
Models predict an increase in the probability of negative yield impacts on key crops (wheat and maize). Two different climate change simulation models were applied, both predicting increased likelihood of crop impacts.
This is an important risk, given the expected increase in demand for food between now and 2050 (see Chapter 4 for more on predictions about future demand for food).
Increased risk of yield losses due to extreme events, but average yield impacts depend on the CO₂ fertilisation effect
See earlier in the chapter for a description of the CO₂ fertilisation effect.
Models have predicted that, with full CO₂ fertilisation, climatic change will not impact average yields so much as yield variability. There will be much greater risk of yield shocks (current 1-in-200 year shocks increase to more like 1-in-20). There may be a decline in nutritional quality too.
Without full CO₂ fertilisation, climatic change will impact yields and yield variability to a much greater extent. Yields that today are unprecedented, become freqent in modelling without CO₂ fertilisation included.
Graphs produced by FCRN from data in Lobell and Tebaldi (2014).
This shows the absolute need to adapt to climate change to ensure yields are maintained.
6.4.2 Negative post-harvest impacts should also be expected.
Post-harvest impacts on food systems must also be considered
Impacts may affect:
Food sourcing, processing and distribution:
- Disruptions to transport & stationary infrastructure
- Unpredictability can lead to crop spoilage & waste
- Food industry may need to change sourcing decisions
- There may be changes in import dependence or export decisions.
- Food safety problems may increase as temperatures increase or humidity levels change, or because of change in the spread of pests and diseases
- Increased use of refrigeration in response to higher temperatures may increase energy use and associated emissions
- There may be changes in consumer demand (i.e. less demand for ‘cold weather’ dishes), which may affect food demand and cooking/refrigeration demand
6.4.3 Increased water stress is expected in various regions.
Climate change will affect water availability and patterns of water stress
Water stress is influenced by the relationship between rainfall, existing groundwater stocks, and water extraction/replenishment rates. These will be influenced by climate change, which will alter precipitation patterns and the prevalence of extreme events, flooding and drought; and will also affect the demand for water for irrigation.
More than 40% of the global population will be living in water stressed regions by 2050
Source: OECD (2012)
Increased water stress is predicted by 2050, especially in river basins with high population densities and increasing water demand. This will include large areas of South Asia, the Middle East, China and North Africa. Over 40% of the world’s population will be living in water stressed river basins by 2050.
Other areas, such as the USA, are predicted to experience less water stress because precipitation is predicted to increase, and because of anticipated gains in the efficiency of water use.
The severity of water stress in high risk areas will depend on water management strategies, and there is need for more efficient water management in both agriculture and in other sectors.
6.4.4 Climate change impacts on marine-sourced foods.
Sea temperature increases and acidification are likely to threaten marine-sourced foods
Climate change impacts will be felt in marine systems as well as on land. One example of this is the degradation of coral reef systems by sea temperature rises; and by increased CO2 concentrations, leading to ocean acidification. Temperature rises and acidification can lead to coral bleaching, whereby the symbiotic algae on which the coral depend are killed; in turn, affecting the organisms dependent on the coral for food and shelter, leading to a loss of biodiversity and damage to ecosystems.
Cesar, Burke and Pet-Soede (2003) estimated that globally, coral reef systems support US$5.7 billion-worth of fishery activity (note that this economic estimation does not account for coral-reef dependent subsistence fishing). Climate change related coral reef degradation, therefore, has the potential for serious marine food system impacts.