Presentation Information
[ACG64-P03]Integrating Terrestrial Nitrogen Limitation into SCM4OPT v4.0 for Long-Term SSP Projections
*Xuanming Su1, Kaoru Tachiiri1 (1.Japan Agency for Marine-Earth Science and Technology)
Keywords:
Reduced-Complexity Models,Climate change,Carbon–nitrogen coupling
Carbon–nitrogen coupling is a key constraint on terrestrial carbon uptake and therefore on climate projections, yet large uncertainties in nitrogen limitation remain a major source of spread across models. Here we extend the emissions-driven simple climate model SCM4OPT, which simulates radiative forcing and global-mean temperature change from a full suite of greenhouse gases, aerosols, and short-lived climate pollutants (as well as land-use albedo), with a simplified global terrestrial nitrogen-cycle module to represent nutrient constraints on land carbon uptake.
The nitrogen module tracks four prognostic pools—vegetation N, litter N, soil organic N, and mineral N—and resolves core fluxes among them, including plant uptake, litterfall, mineralization, leaching, and denitrification, with external inputs from atmospheric deposition, fertilizer application, and biological fixation. Nitrogen availability produces a time-varying limitation factor that is translated into an N-scaling term applied to land net primary production (NPP), coupling nutrient constraints to the terrestrial carbon-cycle equations while preserving internal carbon-mass consistency.
We apply the extended SCM4OPT v4.0 to a set of Shared Socioeconomic Pathways (SSP) scenarios to assess the implications of carbon–nitrogen coupling for long-term projections. Preliminary results suggest that nitrogen limitation reduces global land NPP by approximately 10–15% by 2100 across SSPs spanning low to high emissions, consistent with nitrogen deficits that constrain plant uptake under elevated CO2. These findings highlight that models without an explicit nitrogen cycle can overestimate terrestrial carbon uptake by attributing stronger CO2 fertilization effects to plant growth. Incorporating nitrogen limitation in reduced-complexity climate models provides a practical pathway to improve comparability and realism in assessments of future carbon-cycle feedbacks and climate change.
The nitrogen module tracks four prognostic pools—vegetation N, litter N, soil organic N, and mineral N—and resolves core fluxes among them, including plant uptake, litterfall, mineralization, leaching, and denitrification, with external inputs from atmospheric deposition, fertilizer application, and biological fixation. Nitrogen availability produces a time-varying limitation factor that is translated into an N-scaling term applied to land net primary production (NPP), coupling nutrient constraints to the terrestrial carbon-cycle equations while preserving internal carbon-mass consistency.
We apply the extended SCM4OPT v4.0 to a set of Shared Socioeconomic Pathways (SSP) scenarios to assess the implications of carbon–nitrogen coupling for long-term projections. Preliminary results suggest that nitrogen limitation reduces global land NPP by approximately 10–15% by 2100 across SSPs spanning low to high emissions, consistent with nitrogen deficits that constrain plant uptake under elevated CO2. These findings highlight that models without an explicit nitrogen cycle can overestimate terrestrial carbon uptake by attributing stronger CO2 fertilization effects to plant growth. Incorporating nitrogen limitation in reduced-complexity climate models provides a practical pathway to improve comparability and realism in assessments of future carbon-cycle feedbacks and climate change.