ORCHIDEE_3_r7267

Earth System Models (ESM) represent the time evolution of the biophysical (energy, water cycles) and biogeochemical (carbon cycle) components of the Earth. When used for near-future projections in the context of the Coupled Model Intercomparison Project (CMIP), they use as forcings the evolution of greenhouse gas and other pollutant concentrations and land-use changes simulated by an ensemble of Integrated Assessment Models (IAMs) for a combination of socio-economic pathways and mitigation targets (SSPs). More precisely, only one IAM output is used as representative of a single SSP while the inter-IAM spread is large for ammonia emissions and land-use changes, for instance. This makes the comparison of key ESM diagnostics among SSPs significantly noisy, without the capacity of disentangling SSP-driven and IAM-driven factors. In this paper, we quantify the projected change in land carbon store (CLCS) for the different SSPs with an advanced version of a land surface model embedded into IPSL-CM6 ESM. Through a set of land-only factorial simulations, we specifically aim at estimating the CLCS uncertainties associated with land-use change and nitrogen deposition trajectories. We showed that the spread of the simulated change in global land carbon store induced by the uncertainty on land-use changes is slightly larger than the one associated with the uncertainty on atmospheric CO2. Globally, uncertainty associated with N depositions is responsible for a spread in CLCS lower by a factor three, than the one driven by atmospheric CO2 or land-use changes. Our study calls for making available additional IAM scenarios for each SSP to be used in the next CMIP exercise, in order to specifically assess the IAM-related uncertainty impacts on the carbon cycle and the climate system.地球系统模式（Earth System Models, ESM）刻画了地球生物物理（能量、水循环）与生物地球化学（碳循环）组分的时间演化过程。当用于耦合模式比较计划（Coupled Model Intercomparison Project, CMIP）框架下的近未来预估时，地球系统模式以综合评估模型（Integrated Assessment Models, IAMs）集合模拟的温室气体、其他污染物浓度演变及土地利用变化作为气候强迫场，这些强迫场对应社会经济路径与减缓目标情景（SSPs）的组合。更确切地说，单个社会经济路径情景仅采用单个综合评估模型的输出作为代表，而例如氨排放与土地利用变化的跨综合评估模型差异显著。这使得不同社会经济路径情景间关键地球系统模式诊断量的比较存在显著噪声，无法解耦区分由社会经济路径情景驱动与综合评估模型驱动的影响因素。本研究针对不同社会经济路径情景，借助嵌入IPSL-CM6地球系统模式的先进陆面模式，量化了陆地碳储量（Land Carbon Store, CLCS）的预估变化量。通过一系列纯陆面因子分解模拟，本研究旨在专门估算与土地利用变化、氮沉降轨迹相关的陆地碳储量不确定性。研究表明，由土地利用变化不确定性引发的全球陆地碳储量模拟变化的离散度，略高于由大气CO₂不确定性带来的离散度。全球尺度下，氮沉降相关不确定性导致的陆地碳储量离散度，仅为大气CO₂或土地利用变化驱动的离散度的三分之一。本研究呼吁为每个社会经济路径情景提供更多综合评估模型情景，以供下一代耦合模式比较计划研究使用，从而专门评估与综合评估模型相关的不确定性对碳循环及气候系统的影响。

搜集汇总

背景与挑战

背景概述

ORCHIDEE_3_r7267是ORCHIDEE动态全球植被模型的一个特定版本，主要用于支持全球碳预算评估和未来陆地碳储量变化预测研究。该数据集的核心功能是模拟碳循环过程，特别关注人为二氧化碳排放的再分配以及土地利用变化和氮沉降对陆地碳存储的影响。作为地球系统模型的关键组成部分，它以NETCDF格式提供，服务于气候学和生态学领域的研究与分析。