Global impacts of climate change on yields cannot be estimated due to variation among locations and crop types. But the overall impact on grain is negative—the potential yield loss is about 5 percent for each degree Celsius of global warming.

Lobell et al., 2011

Neil Palmer, CIAT

Extra facts

  • Historical studies demonstrate that climate change has already had negative impacts on crop yields. Maize, wheat and other major crops have experienced significant climate-associated yield reductions of 40 megatonnes per year between 1981 and 2002 at the global level (Lobell and Field 2007).
  • Looking forward, the Intergovernmental Panel on Climate Change (IPCC) consensus is that at mid- to high latitudes, agricultural productivity is likely to increase slightly for local mean temperature increases of 1 to 3 degrees Celsius. In tropical areas, there will be productivity decreases.
  • Uncertainties in projections limit the value of precise numerical forecasts of future crop yields; all projections of future crop yields and associated changes in food prices should be treated with considerable caution (Challinor et al. 2009).
  • Global aggregate figures mask major spatial and temporal variability. In 2030, for example, using a mean of two climate models and two climate scenarios, maize production is projected to increase 18 percent in Kenya but fall 9 percent in Uganda. Within these countries, there is further variability among different agro-ecological zones (Thornton et al. 2010).
  • As climate change progresses, it is increasingly likely that current cropping systems will no longer be viable in many locations. In Africa, for example, under a range of scenarios to 2050, 35 million farmers across 3 percent of the continent’s land area are anticipated to switch from mixed crop-livestock systems to livestock only (Jones and Thorton 2008).
  • Yields of maize and wheat are sensitive to temperatures above 30 degrees Celsius. For example, each day above 30 degrees Celsius in the growing season reduces the final yield of maize by 1 percent under optimal rain-fed conditions and by 1.7 percent under drought conditions (Lobell et al. 2011).
  • Flooding due to climate variability is a significant problem for rice farming, especially in the lowlands of South and Southeast Asia. Flooding already affects about 10 to 15 million hectares of rice fields in South and South East Asia, causing an estimated $1 billion USD in yield losses per year. These losses could increase considerably given sea level rise as well as an increase in the frequencies and intensities of flooding caused by extreme weather events (Bates et al. 2008).
  • Many rainfed rice-growing areas are already drought-prone under present climatic conditions and are likely to experience more intense and more frequent drought events in the future. Drought stress is the largest constraint to rice production in rainfed systems. In Asia, it affect 10 million hectares of upland rice and over 13 million hectares of rainfed lowland rice (Pandey et al. 2007).
  • Results from simulations of a warmer climate (4 degrees Celsius or more in Africa) indicate that projected increases in the length of the growing period projected for parts of East Africa will not necessarily translate into increased agricultural productivity; maize yields are projected to decline by 19 percent despite longer growing periods (Thornton et al. 2011).
  • In current production areas, the likely challenge of pests and diseases will mean that an increased focus on integrated management systems, especially host plant resistance and biological control, is essential. Pests and disease that were once minor problems can turn into major constraints and change their range of distribution with climate change. For example, projections illustrate these effects for three major cassava pests: the mealybug, the cassava green mite and the whitefly (Herrera et al. 2011).
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Methods, caveats and issues

Assumptions and Details:

Interactions among changes in rainfall, temperature, extreme climatic events, atmospheric carbon dioxide concentration and pests and diseases are largely unknown and could substantively affect impacts on crops and their yields in ways that are not yet understood.

There is considerable debate about the role of carbon fertilization of crops under conditions of increased atmospheric carbon dioxide. There is no mechanistic basis for a direct effect of CO2 on C4 photosynthesis and the weight of evidence indicates that in plants, such as maize, C4 photosynthesis is not directly stimulated by elevated CO2. However, growth and yield may benefit indirectly through a reduction in stomatal conductance. Free-Air CO2 Enrichment (FACE) experiments indicate that elevated CO2 improves C4 water relations and so indirectly enhances photosynthesis, growth and yield by delaying and reducing drought stress. In addition, a meta-analysis conducted by Taub et al. (2008) suggests that the increasing CO2 concentrations of the 21st century are likely to decrease the protein concentration of many human plant foods (Thornton et al. 2012).

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  • Herrera B, Hyman G, Belloti A. 2011. Threats to cassava production: known and potential geographic distribution of four key biotic constraints. Food Security 3(3):329–345.
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