Warming Promotes Nitrogen and Carbon Cycles in Global Grassland

Grasslands, standing as one of Earth's major ecosystems, offer numerous services vital to human well-being. The productivity of grasslands hinges on the availability of soil reactive nitrogen, which is highly sensitive to climatic variations. Using an extensive synthesis of 1242 experimental observations, reinforced by multiple models, we show that warming as a single driver of climate change intensifies nitrogen dynamics in grasslands. This could lead to increases in net primary productivity of 1% to 9% and escalate nitrogen leakage into the environment by 22% to 141%. Under the warming SSP2-4.5 scenario, we foresee an annual boost of 17 million tons per year (Tg yr^-1) of nitrogen inputs, predominantly via biological nitrogen fixation, compared to the baseline scenario by 2050. Total nitrogen harvest is projected to climb by 12 Tg yr^-1. However, the nitrogen surplus surge is expected to increase by 5 Tg yr^-1, potentially intensifying nitrogen pollution. To counter this, adaptation measures must aim at curtailing reactive nitrogen losses while preserving increased nitrogen harvest. This could reduce nitrogen input and surplus by 10 and 20 Tg yr^-1, respectively, while boosting nitrogen harvest by 10 Tg yr^-1, potentially yielding economic gains of up to 121 billion USD by 2050. In shaping climate change adaptation policies, it is critical to balance the potential benefits and drawbacks of forging effective management approaches.