June 1, 2020, 7 p.m.
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This graph is based on several studies. See https://en.wikipedia.org/wiki/Climate_change_and_agriculture#cite_note-us_nrc_2011_fig_5.1-52
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). 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) drew on several studies. The graph does not show the "likely" ranges included in US NRC (2011). The likely range means that there is a 67% chance of the projected change in yield being correct, based on expert judgement. 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. The projections do not include measures to adapt to global warming. Actual changes in yields may vary according to local conditions. 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. There is also the possibility that yields will change if critical thresholds are crossed. Many of the uncertainties could bias the projections towards underestimating reductions in crop yields. However, adaptation practices could help to reduce losses in yields. Adaptation will be more difficult for higher magnitudes of warming, and may be less effective in tropical regions. Notes Figure 5.1, p.161, in US NRC 2011 pp.160-162 in US NRC 2011 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, Washington, D.C., USA: National Academies Press