English: This bar graph shows projected changes in yields of selected crops with global warming. Projected changes are shown for 1-4 °C of global warming, relative to late 20th century. Changes in yield are shown for African maize, Asian rice, Indian wheat, US maize, and US soybean. Summary of changes:

• African maize: Declining yields at all temperatures, with reductions increasing with temperature.
• Asian rice: Small increases in yield for 1-2 °C. Yields decrease at 3-4 °C
• Indian wheat: Losses at all temperatures, with losses increasing with temperature.
• US maize: Losses at all temperatures, with losses increasing with temperature.
• US soybean: Gains at 1 °C; no change at 2 °C; and losses at 3-4 °C.

Data

Values are approximate and are taken from the US National Research Council (US NRC, 2011).^[1] The first, second, third and fourth numbers are the projected changes in yields (%) for 1, 2, 3 and 4 °C of global warming, respectively.:

• Africa maize: -14, -25, -37, -46
• Asia rice: +3, +1, -3.5, -7.5
• India wheat: -5, -23, -47, -68
• US maize: -13, -27, -44, -60
• US soybean: +6, 0, -14, -30

These data are also available as comma-separated values.

US NRC (2011)^[1] drew on several studies. The graph does not show the "likely" ranges included in US NRC (2011).^[1] The likely range means that there is a 67% chance of the projected change in yield being correct, based on expert judgement.^[1] For 1 °C of warming, the likely range is roughly equal to plus or minus (±) 5-10% for all projected changes in yields.

• For 2 °C: roughly ± 15-20% for all projected changes in yields.
• For 3 °C: roughly ± 20% for all projected changes " ".
• For 4 °C: roughly ± 30-35% for all projected changes " ".

These projections broadly show the probable changes in regional yields.^[2] The projections do not include measures to adapt to global warming.^[2] Actual changes in yields may vary according to local conditions.^[2] There are numerous other uncertainties, including how local climate will change with global warming, and the atmospheric concentration of carbon dioxide (CO₂) associated with different magnitudes of global warming.^[2] There is also the possibility that yields will change if critical thresholds are crossed.^[2] Many of the uncertainties could bias the projections towards underestimating reductions in crop yields.^[2] However, adaptation practices could help to reduce losses in yields.^[2] Adaptation will be more difficult for higher magnitudes of warming, and may be less effective in tropical regions.^[2]

Notes

References

• US NRC (2011) Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia^[1], Washington, D.C., USA: National Academies Press