Bibliographic record
Abstract
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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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.013 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.002 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.007 | 0.002 |
| Open science | 0.003 | 0.002 |
| Research integrity | 0.019 | 0.011 |
| Insufficient payload (model declined to judge) | 0.160 | 0.139 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".