• Energy Research

Résumé. À l'échelle mondiale, les écosystèmes terrestres ont absorbé environ 30 % des émissions anthropiques au cours de la période 20007-2007 et les gradients interhémisphériques indiquent qu'une fraction importante de la séquestration du carbone terrestre doit se situer au nord de l'équateur. Nous présentons une compilation du bilan de CO2, CO, CH4 et N2O de l'Europe suivant une approche à double contrainte dans laquelle (1) un bilan terrestre dérivé principalement des inventaires de carbone des écosystèmes et (2) un bilan terrestre dérivé des mesures de flux sont confrontés à (3) le bilan atmosphérique dérivé de l'inversion informée par les mesures des concentrations atmosphériques de GES. Un bon accord entre les bilans de GES basés sur les flux (1249 ± 545 Tg C en CO2-eq y−1), les inventaires (1299 ± 200 Tg C en CO2-eq y−1) et les inversions (1210 ± 405 Tg C en CO2-eq y−1) augmente notre confiance que les bilans de GES européens actuels sont exacts. Cependant, l'incertitude reste grande et manque largement d'estimations formelles. Étant donné que les bilans nets terre-atmosphère européens sont déterminés par quelques flux dominants, l'incertitude de ces composantes clés doit être formellement estimée avant que des efforts puissent être déployés pour réduire l'incertitude globale. L'approche à double contrainte a confirmé que la surface terrestre européenne, y compris les eaux intérieures et les zones urbaines, est une source nette de CO2, CO, CH4 et N2O. Cependant, pour tous les écosystèmes à l'exception des terres cultivées, l'absorption de C dépasse les rejets de C et ces 210 ± 70 Tg C y−1 provenant de la combustion de combustibles fossiles sont retirés de l'atmosphère et séquestrés dans les écosystèmes aquatiques terrestres et intérieurs. Si le coût du carbone pour la gestion des écosystèmes est pris en compte, l'absorption nette des écosystèmes a été estimée à diminuer de 45 %, mais indique toujours une séquestration substantielle du carbone. En outre, lorsque l'équilibre est étendu du CO2 vers les principaux GES, l'absorption de C par les écosystèmes terrestres et aquatiques est compensée par les émissions de GES. En tant que tels, les écosystèmes européens sont peu susceptibles de contribuer à atténuer les effets du changement climatique. Resumen. A nivel mundial, los ecosistemas terrestres han absorbido alrededor del 30% de las emisiones antropogénicas durante el período 20007-2007 y los gradientes interhemisféricos indican que una fracción significativa del secuestro de carbono terrestre debe estar al norte del Ecuador. Presentamos una recopilación del balance de CO2, CO, CH4 y N2O de Europa siguiendo un enfoque de doble restricción en el que (1) un balance terrestre derivado principalmente de los inventarios de carbono del ecosistema y (2) un balance terrestre derivado de las mediciones de flujo se enfrentan con (3) el balance atmosférico derivado de la inversión informada por las mediciones de las concentraciones atmosféricas de GEI. Una buena concordancia entre los balances de GEI basados en flujos (1249 ± 545 Tg C en CO2-eq y−1), inventarios (1299 ± 200 Tg C en CO2-eq y−1) e inversiones (1210 ± 405 Tg C en CO2-eq y−1) aumenta nuestra confianza en que los balances de GEI europeos actuales son precisos. Sin embargo, la incertidumbre sigue siendo grande y en gran medida carece de estimaciones formales. Dado que los balances netos tierra-atmósfera europeos están determinados por unos pocos flujos dominantes, la incertidumbre de estos componentes clave debe estimarse formalmente antes de poder realizar esfuerzos para reducir la incertidumbre general. El enfoque de doble restricción confirmó que la superficie terrestre europea, incluidas las aguas interiores y las zonas urbanas, es una fuente neta de CO2, CO, CH4 y N2O. Sin embargo, para todos los ecosistemas, excepto las tierras de cultivo, la absorción de C excede la liberación de C y tales 210 ± 70 Tg C y−1 de la quema de combustibles fósiles se eliminan de la atmósfera y se secuestran en los ecosistemas acuáticos terrestres y continentales. Si se tiene en cuenta el costo de C para la gestión de los ecosistemas, se estimó que la absorción neta de los ecosistemas disminuiría en un 45%, pero aún indica un secuestro sustancial de C. Además, cuando el equilibrio se extiende desde el CO2 hacia los principales GEI, la absorción de C por los ecosistemas terrestres y acuáticos se compensa con las emisiones de GEI. Como tal, es poco probable que los ecosistemas europeos contribuyan a mitigar los efectos del cambio climático. Abstract. Globally, terrestrial ecosystems have absorbed about 30% of anthropogenic emissions over the period 20007–2007 and inter-hemispheric gradients indicate that a significant fraction of terrestrial carbon sequestration must be north of the Equator. We present a compilation of the CO2, CO, CH4 and N2O balance of Europe following a dual constraint approach in which (1) a land-based balance derived mainly from ecosystem carbon inventories and (2) a land-based balance derived from flux measurements are confronted with (3) the atmospheric-based balance derived from inversion informed by measurements of atmospheric GHG concentrations. Good agreement between the GHG balances based on fluxes (1249 ± 545 Tg C in CO2-eq y−1), inventories (1299 ± 200 Tg C in CO2-eq y−1) and inversions (1210 ± 405 Tg C in CO2-eq y−1) increases our confidence that current European GHG balances are accurate. However, the uncertainty remains large and largely lacks formal estimates. Given that European net land-atmosphere balances are determined by a few dominant fluxes, the uncertainty of these key components needs to be formally estimated before efforts could be made to reduce the overall uncertainty. The dual-constraint approach confirmed that the European land surface, including inland waters and urban areas, is a net source for CO2, CO, CH4 and N2O. However, for all ecosystems except croplands, C uptake exceeds C release and us such 210 ± 70 Tg C y−1 from fossil fuel burning is removed from the atmosphere and sequestered in both terrestrial and inland aquatic ecosystems. If the C cost for ecosystem management is taken into account, the net uptake of ecosystems was estimated to decrease by 45% but still indicates substantial C-sequestration. Also, when the balance is extended from CO2 towards the main GHGs, C-uptake by terrestrial and aquatic ecosystems is compensated for by emissions of GHGs. As such the European ecosystems are unlikely to contribute to mitigating the effects of climate change. الخلاصة. على الصعيد العالمي، امتصت النظم الإيكولوجية الأرضية حوالي 30 ٪ من الانبعاثات البشرية المنشأ خلال الفترة 20007-2007 وتشير التدرجات بين نصف الكرة الأرضية إلى أن جزءًا كبيرًا من عزل الكربون الأرضي يجب أن يكون شمال خط الاستواء. نقدم مجموعة من توازن ثاني أكسيد الكربون وثاني أكسيد الكربون والميثان وأكسيد النيتروز في أوروبا باتباع نهج القيد المزدوج الذي (1) يواجه فيه التوازن البري المستمد بشكل أساسي من قوائم جرد الكربون في النظام الإيكولوجي و (2) التوازن البري المستمد من قياسات التدفق (3) التوازن الجوي المستمد من الانعكاس المستنير بقياسات تركيزات غازات الدفيئة في الغلاف الجوي. الاتفاق الجيد بين أرصدة غازات الدفيئة على أساس التدفقات (1249 ± 545 تيراغرام C في مكافئ ثاني أكسيد الكربون y-1)، والمخزونات (1299 ± 200 تيراغرام C في مكافئ ثاني أكسيد الكربون y-1) والانقلابات (1210 ± 405 تيراغرام C في مكافئ ثاني أكسيد الكربون y-1) يزيد من ثقتنا في أن أرصدة غازات الدفيئة الأوروبية الحالية دقيقة. ومع ذلك، لا يزال عدم اليقين كبيرًا ويفتقر إلى حد كبير إلى التقديرات الرسمية. وبالنظر إلى أن صافي الأرصدة الأوروبية للأرض والغلاف الجوي يتحدد بعدد قليل من التدفقات المهيمنة، فإن عدم اليقين في هذه المكونات الرئيسية يحتاج إلى تقدير رسمي قبل أن يتسنى بذل الجهود للحد من عدم اليقين العام. أكد نهج التقييد المزدوج أن سطح الأرض الأوروبي، بما في ذلك المياه الداخلية والمناطق الحضرية، هو مصدر صافي لثاني أكسيد الكربون وثاني أكسيد الكربون والميثان وأكسيد النيتروز. ومع ذلك، بالنسبة لجميع النظم الإيكولوجية باستثناء الأراضي الزراعية، يتجاوز الامتصاص C إطلاق C ويتم إزالة 210 ± 70 Tg Cy -1 من حرق الوقود الأحفوري من الغلاف الجوي ويتم عزله في كل من النظم الإيكولوجية المائية الأرضية والداخلية. إذا تم أخذ التكلفة "ج" لإدارة النظم الإيكولوجية في الاعتبار، فقد قُدر أن صافي امتصاص النظم الإيكولوجية سينخفض بنسبة 45 ٪ ولكنه لا يزال يشير إلى تسلسل "ج" كبير. أيضًا، عندما يتم تمديد الرصيد من ثاني أكسيد الكربون إلى غازات الدفيئة الرئيسية، يتم تعويض امتصاص الكربون من قبل النظم الإيكولوجية الأرضية والمائية بانبعاثات غازات الدفيئة. على هذا النحو، من غير المرجح أن تساهم النظم الإيكولوجية الأوروبية في التخفيف من آثار تغير المناخ.

We improved a process‐oriented biogeochemical model of carbon and nitrogen cycling in grasslands and tested it against in situ measurements of biomass and CO2 and CH4 fluxes at five European grassland sites. The new version of the model (PASIM) calculates the growth and senescence of aboveground vegetation biomass accounting for sporadic removals when the grassland is cut and for continuous removals when it is grazed. Limitations induced by high leaf area index (LAI), soil water deficits and aging of leaves are also included. We added to this a simple empirical formulation to account for the detrimental impact on vegetation of trampling and excreta by grazing animals. Finally, a more realistic methane emission module than is currently used was introduced on the basis of the quality of the animals' diet. Evaluation of this improved version of PASIM is performed at (1) Laqueuille, France, on grassland continuously grazed by cattle with two plots of intensive and extensive grazing intensities, (2) Oensingen, Switzerland, on cut grassland with two fertilized and nonfertilized plots, and (3) Carlow, Ireland, on grassland that is both cut and grazed by cattle during the growing season. In addition, we compared the modeled animal CH4 emissions with in situ measurements on cattle for two grazing intensities at the grazed grassland site of Laqueuille. Altogether, when all improvements to the PASIM model are included, we found that the new parameterizations resulted into a better fit to the observed seasonal cycle of biomass and of measured CO2 and CH4 fluxes. However, the large uncertainties in measurements of biomass and LAI make simulation of biomass dynamics difficult to make. Also simulations for cut grassland are better than for grazed swards. This work paves the way for simulating greenhouse gas fluxes over grasslands in a spatially explicit manner, in order to quantify and understand the past, present and future role of grasslands in the greenhouse gas budget of the European continent.

AbstractChanging amplitude of the seasonal cycle of atmospheric CO2 (SCA) in the northern hemisphere is an emerging carbon cycle property. Mauna Loa (MLO) station (20°N, 156°W), which has the longest continuous northern hemisphere CO2 record, shows an increasing SCA before the 1980s (p < .01), followed by no significant change thereafter. We analyzed the potential driving factors of SCA slowing‐down, with an ensemble of dynamic global vegetation models (DGVMs) coupled with an atmospheric transport model. We found that slowing‐down of SCA at MLO is primarily explained by response of net biome productivity (NBP) to climate change, and by changes in atmospheric circulations. Through NBP, climate change increases SCA at MLO before the 1980s and decreases it afterwards. The effect of climate change on the slowing‐down of SCA at MLO is mainly exerted by intensified drought stress acting to offset the acceleration driven by CO2 fertilization. This challenges the view that CO2 fertilization is the dominant cause of emergent SCA trends at northern sites south of 40°N. The contribution of agricultural intensification on the deceleration of SCA at MLO was elusive according to land–atmosphere CO2 flux estimated by DGVMs and atmospheric inversions. Our results also show the necessity to adequately account for changing circulation patterns in understanding carbon cycle dynamics observed from atmospheric observations and in using these observations to benchmark DGVMs.

Abstract. Nitrous oxide (N2O) is a long-lived potent greenhouse gas and stratospheric ozone-depleting substance that has been accumulating in the atmosphere since the preindustrial period. The mole fraction of atmospheric N2O has increased by nearly 25 % from 270 ppb (parts per billion) in 1750 to 336 ppb in 2022, with the fastest annual growth rate since 1980 of more than 1.3 ppb yr−1 in both 2020 and 2021. According to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR6), the relative contribution of N2O to the total enhanced effective radiative forcing of greenhouse gases was 6.4 % for 1750–2022. As a core component of our global greenhouse gas assessments coordinated by the Global Carbon Project (GCP), our global N2O budget incorporates both natural and anthropogenic sources and sinks and accounts for the interactions between nitrogen additions and the biogeochemical processes that control N2O emissions. We use bottom-up (BU: inventory, statistical extrapolation of flux measurements, and process-based land and ocean modeling) and top-down (TD: atmospheric measurement-based inversion) approaches. We provide a comprehensive quantification of global N2O sources and sinks in 21 natural and anthropogenic categories in 18 regions between 1980 and 2020. We estimate that total annual anthropogenic N2O emissions have increased 40 % (or 1.9 Tg N yr−1) in the past 4 decades (1980–2020). Direct agricultural emissions in 2020 (3.9 Tg N yr−1, best estimate) represent the large majority of anthropogenic emissions, followed by other direct anthropogenic sources, including fossil fuel and industry, waste and wastewater, and biomass burning (2.1 Tg N yr−1), and indirect anthropogenic sources (1.3 Tg N yr−1) . For the year 2020, our best estimate of total BU emissions for natural and anthropogenic sources was 18.5 (lower–upper bounds: 10.6–27.0) Tg N yr−1, close to our TD estimate of 17.0 (16.6–17.4) Tg N yr−1. For the 2010–2019 period, the annual BU decadal-average emissions for both natural and anthropogenic sources were 18.2 (10.6–25.9) Tg N yr−1 and TD emissions were 17.4 (15.8–19.20) Tg N yr−1. The once top emitter Europe has reduced its emissions by 31 % since the 1980s, while those of emerging economies have grown, making China the top emitter since the 2010s. The observed atmospheric N2O concentrations in recent years have exceeded projected levels under all scenarios in the Coupled Model Intercomparison Project Phase 6 (CMIP6), underscoring the importance of reducing anthropogenic N2O emissions. To evaluate mitigation efforts and contribute to the Global Stocktake of the United Nations Framework Convention on Climate Change, we propose the establishment of a global network for monitoring and modeling N2O from the surface through to the stratosphere. The data presented in this work can be downloaded from https://doi.org/10.18160/RQ8P-2Z4R (Tian et al., 2023).

Project: Coupled Model Intercomparison Project Phase 6 (CMIP6) datasets - These data have been generated as part of the internationally-coordinated Coupled Model Intercomparison Project Phase 6 (CMIP6; see also GMD Special Issue: http://www.geosci-model-dev.net/special_issue590.html). The simulation data provides a basis for climate research designed to answer fundamental science questions and serves as resource for authors of the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR6). CMIP6 is a project coordinated by the Working Group on Coupled Modelling (WGCM) as part of the World Climate Research Programme (WCRP). Phase 6 builds on previous phases executed under the leadership of the Program for Climate Model Diagnosis and Intercomparison (PCMDI) and relies on the Earth System Grid Federation (ESGF) and the Centre for Environmental Data Analysis (CEDA) along with numerous related activities for implementation. The original data is hosted and partially replicated on a federated collection of data nodes, and most of the data relied on by the IPCC is being archived for long-term preservation at the IPCC Data Distribution Centre (IPCC DDC) hosted by the German Climate Computing Center (DKRZ). The project includes simulations from about 120 global climate models and around 45 institutions and organizations worldwide. Summary: These data include the subset used by IPCC AR6 WGI authors of the datasets originally published in ESGF for 'CMIP6.LS3MIP.IPSL.IPSL-CM6A-LR' with the full Data Reference Syntax following the template 'mip_era.activity_id.institution_id.source_id.experiment_id.member_id.table_id.variable_id.grid_label.version'. The IPSL-CM6A-LR climate model, released in 2017, includes the following components: atmos: LMDZ (NPv6, N96; 144 x 143 longitude/latitude; 79 levels; top level 80000 m), land: ORCHIDEE (v2.0, Water/Carbon/Energy mode), ocean: NEMO-OPA (eORCA1.3, tripolar primarily 1deg; 362 x 332 longitude/latitude; 75 levels; top grid cell 0-2 m), ocnBgchem: NEMO-PISCES, seaIce: NEMO-LIM3. The model was run by the Institut Pierre Simon Laplace, Paris 75252, France (IPSL) in native nominal resolutions: atmos: 250 km, land: 250 km, ocean: 100 km, ocnBgchem: 100 km, seaIce: 100 km.

Abstract. The responses of crop functioning to changing climate and atmospheric CO2 concentration ([CO2]) could have large effects on food production, and impact carbon, water and energy fluxes, causing feedbacks to climate. To simulate the responses of temperate crops to changing climate and [CO2], accounting for the specific phenology of crops mediated by management practice, we present here the development of a process-oriented terrestrial biogeochemical model named ORCHIDEE-CROP (v0), which integrates a generic crop phenology and harvest module and a very simple parameterization of nitrogen fertilization, into the land surface model (LSM) ORCHIDEEv196, in order to simulate biophysical and biochemical interactions in croplands, as well as plant productivity and harvested yield. The model is applicable for a range of temperate crops, but it is tested here for maize and winter wheat, with the phenological parameterizations of two European varieties originating from the STICS agronomical model. We evaluate the ORCHIDEE-CROP (v0) model against eddy covariance and biometric measurements at 7 winter wheat and maize sites in Europe. The specific ecosystem variables used in the evaluation are CO2 fluxes (NEE), latent heat and sensible heat fluxes. Additional measurements of leaf area index (LAI), aboveground biomass and yield are used as well. Evaluation results reveal that ORCHIDEE-CROP (v0) reproduces the observed timing of crop development stages and the amplitude of pertaining LAI changes in contrast to ORCHIDEEv196 in which by default crops have the same phenology than grass. A near-halving of the root mean square error of LAI from 2.38 ± 0.77 to 1.08 ± 0.34 m2 m−2 is obtained between ORCHIDEEv196 and ORCHIDEE-CROP (v0) across the 7 study sites. Improved crop phenology and carbon allocation lead to a general good match between modelled and observed aboveground biomass (with a normalized root mean squared error (NRMSE) of 11.0–54.2 %), crop yield, as well as of the daily carbon and energy fluxes with NRMSE of ~9.0–20.1 and ~9.4–22.3 % for NEE, and sensible and latent heat fluxes, respectively. The model data mistfit for energy fluxes are within uncertainties of the measurements, which themselves show an incomplete energy balance closure within the range 80.6–86.3 %. The remaining discrepancies between modelled and observed LAI and other variables at specific sites are partly attributable to unrealistic representation of management events. In addition, ORCHIDEE-CROP (v0) is shown to have the ability to capture the spatial gradients of carbon and energy-related variables, such as gross primary productivity, NEE, sensible heat fluxes and latent heat fluxes, across the sites in Europe, an important requirement for future spatially explicit simulations. Further improvement of the model with an explicit parameterization of nutrition dynamics and of management, is expected to improve its predictive ability to simulate croplands in an Earth System Model.