English: This bar graph shows projected changes in crop yields at different latitudes with global warming. Projected changes are shown for 1-3 °C of global warming, relative to late 20th century. For mid-to-high latitudes, changes in yield are shown for wheat and maize. For low-latitudes, changes are shown for wheat, rice and maize. In mid-to-high latitudes:

• wheat yields increase for warming of 1-2 °C. Yields decrease at 3 °C.
• maize yields are unchanged for 1 °C of warming. Yields decrease at 2-3 °C

In low latitudes:

• wheat and rice yields are unchanged at 1 °C. They decrease at 2-3 °C.
• maize yields decrease at 1-3 °C.

Data

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

• Mid-to-high latitude wheat: +10, +4, -16
• Mid-to-high latitude maize: 0,-4,-7
• Low latitude wheat: 0, -20, -40
• Low latitude rice: 0, -8, -16
• Low latitude maize: -5, -18, -40

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 global warming, the likely range is roughly equal to plus or minus (+/-) 10% for all projected changes in yields. Uncertainty increases with temperature. For 3 °C of warming, the likely range is roughly:

• +/- 10% for mid-to-high latitude wheat, mid-to-high latitude maize, and low-latitude rice;
• +/- 20% for low-latitude wheat and low-latitude maize.

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), “Sec 5.1 FOOD PRODUCTION, PRICES, AND HUNGER, in: Ch 5: Impacts in the Next Few Decades and Coming Centuries”, in Climate Stabilization Targets: Emissions, Concentrations, and Impacts over Decades to Millennia^[1], Washington, D.C., USA: National Academies Press