Climate change, agriculture and food – from a course at Open University:
A decrease in food security and a breakdown in the global food system are identified as some of the most significant risks from climate change. Poorer parts of the world are most at risk.
All aspects of food security are potentially affected by climate change including: food availability, access and utilisation, as well as price stability.
How will climate change affect agriculture?
Crop production: negative impacts
Crops are highly sensitive to climate, with crop growth, production and yield dependent on temperature, rainfall and CO2 concentration. Changes in climate can have negative and positive effects on crops.
Many crops respond to increasing temperature by shortening the time to maturity which results in reduced yields. Wheat and maize, two of the world’s major food crops, have already been adversely affected by rising temperatures, resulting in a net decrease in global yields. Although soybean yields have decreased in some growing areas, the decrease has been less severe. The yield and quality of rice has been negatively affected by warmer night time temperatures.
High temperature during flowering also decreases grain set in a number of crops. In general, temperatures exceeding 30-34°C negatively impact crop yields and temperatures in excess of 33°C result in rice spikelet sterility.
Figure 1: The estimated impacts of observed climate changes on yields of major crops over 1960-2013. The numbers above the bars show the number of studies assessed. Source: IPCC WGII AR5 (2014) – Fig TS-2E from the Technical Summary of the IPCC (2014) Working Group II assessment report.
Ozone at the surface (an air pollutant produced from vehicle exhausts and other processes) can damage crops. It is estimated that the increase in tropospheric ozone since pre-industrial times could have reduced yields of wheat and soybean by around 10% for example.
Food production can also be negatively affected by climate-related extremes, including heat waves, droughts and floods, which occur less frequently but often have devastating impacts on crops and livestock.
Crop production: positive impacts
Changes in climate can also have beneficial impacts on crops, for example the reduction in the number of frost occurrences since 1961. Some positive impacts of climate change have been identified, mostly in cooler, high latitude regions.
An increase in carbon dioxide levels can stimulate plant growth and increase yields (often referred to as ‘CO2 fertilisation’). This is especially the case for C3 crops (e.g., wheat, rice, cotton, soybean, sugar beets, and potatoes). However, the response to increasing CO2 in the atmosphere depends on temperature, the availability of water and nutrients and the levels of air pollution. So there is considerable uncertainty about the effect of CO2 fertilisation in the future.
Crop productions: future impacts
Negative impacts on global crop yields become likely by the 2030s. With yield decreases of 0 to 2% per decade projected for the rest of the century. These impacts will occur in the context of rising crop demand, which is projected to increase by about 14% per decade until 2050. Adaptation, such as the use of heat or drought tolerant crop varieties, could significantly reduce negative impacts of climate change and increase the benefit of positive changes. Such adaptation will be highly specific to regions and systems of agriculture.
After 2050 the risk of more severe impacts increases and the ability to adapt to such impacts becomes more difficult.
Weeds, pests and diseases
Recent evidence suggests that changes in climate and increasing CO2levels could enhance the distribution and competiveness of weeds (which compete with food crops and potentially reduce yields). Some of the worst weeds are often wild relatives of the domesticated crop species (e.g., ‘red rice’).
With increased CO2, the growth of such weeds is likely to be stimulated, resulting in reduced crop yields. Some studies have also suggested that rising CO2 could reduce the effectiveness of the herbicides used to kill and control weeds. For example, the invasive Canadian thistle produces a larger root system under elevated CO2 levels and this dilutes the effect of the herbicide which is absorbed within the plant roots.
Climate change may alter the geographical ranges of crop pests and diseases and may also increase disease intensity. However, the overall effects are uncertain.
Livestock varieties have been selected to increase productivity (e.g., cattle with increased milk yield or poultry with increased growth rates). However, such selection for productivity produces animals with lower heat tolerance. For example, this results in increased mortality and financial losses of dairy cows in response to heat stress.
Embryonic development and reproductive efficiency in pigs will be negatively affected by increased temperature and heat stress impacts ovulation and follicle development in horses. Water availability may limit livestock production, particularly in water-scare regions.
How will climate change affect food prices?
The price of food is an important aspect of food security – especially for poorer people who are likely to spend a larger proportion of their income on food. The price of internationally traded foods, such as wheat, maize and soy, reflects the overall balance of supply and demand.
During much of the 20th century, food prices have been declining, but in the last decade there have been several periods where food prices have increased rapidly. A major cause for this recent increase in price volatility has been increased demand for crops, partly as a result of increased biofuel production which in turn is linked to policy changes and oil price fluctuations. Fluctuations in food production are also considered to have played a major role and recent price spikes often follow climate extremes in producer regions.
While food prices result from a complex interaction of physical, economic and policy influences, climate change could contribute to increased food prices over the 21st century. In addition, future increases in the frequency and severity of climate extremes are likely to add to short-term variability of food prices.
Figure 2. The history of food and cereal prices since 1990. Vertical lines and text boxes indicate events when crop yields dropped significantly in producer regions indicative of a seasonal climate extreme. Food and cereal prices are also clearly also linked to the price of crude oil. Source: IPCC WGII AR5 (2014) – Fig 7-3 fromChapter 7 of the IPCC (2014) Working Group II assessment report.
- Briefing on climate change and agriculture
- Using climate analogues to investigate adaptation of agriculture to climate change