Preprints
https://doi.org/10.5194/bg-2023-96
https://doi.org/10.5194/bg-2023-96
04 Jul 2023
 | 04 Jul 2023
Status: a revised version of this preprint is currently under review for the journal BG.

Effect of terrestrial nutrient limitation on the estimation of the remaining carbon budget

Makcim L. De Sisto and Andrew H. MacDougall

Abstract. The carbon cycle plays a foundational role in the estimation of the remaining carbon budget. It is intrinsic for the determination of the transient climate response to cumulative CO2 emissions and the zero emissions commitment. For the terrestrial carbon cycle, nutrient limitation has a core regulation on the amount of carbon fixed by terrestrial vegetation. Hence, the addition of nutrients such as nitrogen and phosphorus in land model structures in Earth system models is essential for an accurate representation of the carbon cycle feedback in future climate projections. Thereby, the estimation of the remaining carbon budget is impacted by the representation of nutrient limitation in modelled terrestrial ecosystems, yet it is rarely accounted for. Here, we estimate the carbon budget and remaining carbon budget of a nutrient limited Earth system model, using nitrogen and phosphorus cycles to limit vegetation productivity and biomass. We use eight Shared Socioeconomic Pathways scenarios and idealized experiments on three distinct model structures: 1) carbon cycle without nutrient limitation, 2) carbon cycle with terrestrial nitrogen limitation and 3) carbon cycle with terrestrial nitrogen and phosphorus limitation. To capture the uncertainty of the remaining carbon budget, three different climate sensitives were tuned for each model version. Our results show that overall the nutrient limitation reduced the remaining carbon budget for all simulations in comparison with the carbon cycle without nutrient limitation. Between the nitrogen and nitrogen-phosphorus limitation, the latter had the lowest remaining carbon budget. The mean remaining carbon budget from the Shared Socioeconomic Pathways scenarios simulations for the 1.5 °C target in the no nutrient limitation, nitrogen limited and nitrogen-phosphorus limited models obtained were 228, 185 and 175 Pg C respectively, relative to year 2020. For the 2 °C target the mean remaining carbon budget were 471, 373 and 351 Pg C for the no nutrient limitation, nitrogen limited and nitrogen-phosphorus limited models respectively, relative to year 2020. This represents a reduction of 19 and 24 % for the 1.5 °C target and 21 and 26 % for the 2 °C target in the nitrogen and nitrogen-phosphorus limited simulations compared to the no nutrient limitation model. These results show that terrestrial nutrient limitations constitute an important factor to be considered when estimating or interpreting remaining carbon budgets and are an essential uncertainty of remaining carbon budgets from Earth system model simulations.

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Makcim L. De Sisto and Andrew H. MacDougall

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-96', Anonymous Referee #1, 21 Jul 2023
    • AC1: 'Reply on RC1', Makcim Luis De Sisto Lelchitskaya, 07 Nov 2023
  • RC2: 'Comment on bg-2023-96', Anonymous Referee #2, 11 Sep 2023
    • AC3: 'Reply on RC2', Makcim Luis De Sisto Lelchitskaya, 07 Nov 2023
  • RC3: 'Comment on bg-2023-96', Anonymous Referee #3, 14 Sep 2023
    • AC2: 'Reply on RC3', Makcim Luis De Sisto Lelchitskaya, 07 Nov 2023
Makcim L. De Sisto and Andrew H. MacDougall
Makcim L. De Sisto and Andrew H. MacDougall

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Short summary
There is uncertainty about the amount of CO2 that can still be emitted to reach specific temperature targets. One source of uncertainty is the representation of the carbon cycle. We assessed the impact of terrestrial nitrogen and phosphorus limitation. We found a reduction in the amount of CO2 that can still be emitted to reach temperature targets in the nutrient limited simulations. We found that nutrient limitation is an important factor to consider when estimating remaining carbon budgets.
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