Future warming increases probability of globally synchronized maize production shocks

Abstract

Meeting the global food demand of roughly 10 billion people by the middle of the 21st century will become increasingly challenging as the Earth's climate continues to warm. Earlier studies suggest that once the optimum growing temperature is exceeded, mean crop yields decline and the variability of yield increases even if interannual climate variability remains unchanged. Here, we use global datasets of maize production and climate variability combined with future temperature projections to quantify how yield variability will change in the world's major maize-producing and -exporting countries under 2 °C and 4 °C of global warming. We find that as the global mean temperature increases, absent changes in temperature variability or breeding gains in heat tolerance, the coefficient of variation (CV) of maize yields increases almost everywhere to values much larger than present-day values. This higher CV is due both to an increase in the SD of yields and a decrease in mean yields. For the top four maize-exporting countries, which account for 87% of global maize exports, the probability that they have simultaneous production losses greater than 10% in any given year is presently virtually zero, but it increases to 7% under 2 °C warming and 86% under 4 °C warming. Our results portend rising instability in global grain trade and international grain prices, affecting especially the ∼800 million people living in extreme poverty who are most vulnerable to food price spikes. They also underscore the urgency of investments in breeding for heat tolerance.

Keywords: climate change; food security; price volatility.

Fig. 1.

Schematic representation of temperature-yield relationship. In the absence of breeding for heat tolerance, an increase in mean temperature beyond the optimum temperature (♦) will lead to a decrease in mean yield and an increase in yield variability, assuming interannual temperature variability stays the same.

Fig. 2.

Warming-induced changes in mean yield. Relative change in average yield (%) following annual mean global warming of 2 °C (Left) and 4 °C (Right).

Fig. 3.

Warming-induced changes in yield variability. (Top) Present-day CV due to all sources of variability (Left) and climate variability (Right). (Bottom) Ratio of changes in climate-driven CV following annual mean global warming of 2 °C (Left) and 4 °C (Right).

Fig. 4.

Warming-induced changes in yield variability in top-producing regions of the six largest maize-producing and -exporting countries (SI Appendix, Table S2): Probability density functions of yield anomalies with respect to present-day mean yield for present-day climate (black), following 2 °C of annual mean global warming (blue), and following 4 °C of annual mean global warming (red). The vertical gray line denotes a relative yield reduction of 20%, and boxed values indicate mean present-day yield in these areas for present-day climate (1999–2008; black) and for 2 °C (blue) and 4 °C (red) warming.