Increased greenhouse-gas intensity of rice production under future atmospheric conditions

Increased atmospheric CO₂ and rising temperatures are expected to affect rice yields and greenhouse-gas (GHG) emissions from rice paddies^{1, 2, 3, 4}. This is important, because rice cultivation is one of the largest human-induced sources of the potent GHG methane⁵ (CH₄) and rice is the world’s second-most produced staple crop⁶. The need for meeting a growing global food demand⁷ argues for assessing GHG emissions from croplands on the basis of yield rather than land area^{8, 9, 10}, such that efforts to reduce GHG emissions take into consideration the consequences for food production. However, it is unclear whether or how the GHG intensity (that is, yield-scaled GHG emissions) of cropping systems will be affected by future atmospheric conditions. Here we show, using meta-analysis, that increased atmospheric CO₂ (ranging from 550 to 743 ppmV) and warming (ranging from +0.8 °C to +6 °C) both increase the GHG intensity of rice cultivation. Increased atmospheric CO₂ increased GHG intensity by 31.4%, because CH₄ emissions are stimulated more than rice yields. Warming increased GHG intensity by 11.8% per 1 °C, largely owing to a decrease in yield. This analysis suggests that rising CO₂ and warming will approximately double the GHG intensity of rice production by the end of the twenty-first century, stressing the need for management practices that optimize rice production while reducing its GHG intensity as the climate continues to change.