Nitrogen cycles in global croplands altered by elevated CO2

Abstract

Croplands are the foundation of global food security and represent the largest nitrogen flows on Earth. Elevated atmospheric CO2 levels are a key driver of climate change with multiple impacts on food production and environmental sustainability. However, our understanding of how the cropland nitrogen cycle responds to elevated CO2 levels is not well developed. Here we demonstrate that elevated CO2 (eCO2) alone would induce a synergistic intensification of the nitrogen and carbon cycles, promoting nitrogen-use efficiency by 19% (95% confidence interval, 14–26%) and biological nitrogen fixation by 55% (95% confidence interval, 28–85%) in global croplands. This would lead to increased crop nitrogen harvest (+12 Tg yr−1), substantially lower fertilizer input requirements (−34 Tg yr−1) and an overall decline in reactive nitrogen loss (−46 Tg yr−1) under future eCO2 scenarios by 2050. The impact of eCO2 on the altered cropland nitrogen cycle would amount to US$668 bn of societal benefits by avoiding damages to human and ecosystem health. The largest benefits are expected to materialize in China, India, North America and Europe. It is paramount to incorporate the effect of rising CO2 on the nitrogen cycle into state-of-the-art Earth system models to provide robust scientific evidence for policymaking. Current understanding of how the cropland nitrogen cycle will respond to elevated atmospheric CO2 is limited. By modelling global nitrogen budgets under elevated CO2 and providing a monetized impact assessment, this study shows the synergistic effects of elevated CO2 alone on global croplands.