Nitrogen limitation amplifies future warming by weakening terrestrial carbon cycle feedbacks and sink capacity

Abstract The inclusion of the terrestrial nitrogen cycle in Earth system models (ESMs) represents a major advance, yet its role in fully coupled climate–carbon–nitrogen dynamics remains underexplored. Using MAGICC-CNit to emulate CMIP6 ESMs, we present the first emission-driven, probabilistic cross-ESM projections of climate–carbon–nitrogen interactions and global carbon budgets across SSP1-2.6 to SSP5-8.5 scenarios. Nitrogen limitation weakens the carbon–concentration feedback by 37% (from 1.10 ± 0.36 to 0.70 ± 0.37 GtC ppm⁻¹) and the carbon–climate feedback by 16% (from −53.35 ± 37.53 to –44.6 ± 30.1 GtC °C⁻¹), reducing land carbon uptake (18-54%) and increasing atmospheric CO₂ ( + 15–57 ppm) and global warming ( + 0.16–0.25 °C) by 2100, with high-emission scenarios risking land becoming a net carbon source. Carbon-only ESMs implicitly capture nitrogen constraints historically but not future impacts, reinforcing the need for explicit coupling. These findings provide an internally consistent quantification of nitrogen’s role in coupled climate–carbon dynamics across ESMs and scenarios, highlighting the value of physically based emulators as a self-consistent framework for advancing projections.