• Energy Research

La croissance accrue de la végétation par le réchauffement climatique joue un rôle central dans l'amplification du cycle saisonnier du CO2 atmosphérique sur les terres nordiques (>50° N) depuis les années 1960. Cependant, la corrélation entre la croissance de la végétation, la température et l'amplitude saisonnière de la concentration de CO2 atmosphérique est devenue insaisissable avec le ralentissement de la tendance à la hausse de la croissance de la végétation et l'affaiblissement du contrôle de la température sur l'absorption de CO2 depuis la fin des années 1990. Ici, sur la base des enregistrements de concentration de CO2 atmosphérique in situ du site de l'observatoire Barrow, nous avons constaté un ralentissement de la tendance à la hausse de l'amplitude du CO2 atmosphérique des années 1990 au milieu des années 2000. Ce phénomène était associé à la diminution en pause de la concentration minimale de CO2 ([CO2]min), qui était significativement corrélée au ralentissement du verdissement de la végétation et à l'extension de la longueur de la saison de croissance. Nous avons ensuite montré que la verdure de la végétation et la longueur de la saison de croissance étaient positivement corrélées avec la température du printemps mais pas celle de l'automne sur les terres du nord. En outre, de telles dépendances asymétriques de la croissance de la végétation sur la température du printemps et de l'automne ne peuvent pas être capturées par les modèles de biosphère terrestre de pointe. Ces résultats indiquent que les réponses de la croissance de la végétation au réchauffement du printemps et de l'automne sont asymétriques et soulignent la nécessité d'améliorer la phénologie de l'automne dans les modèles de prévision du cycle saisonnier de la concentration atmosphérique de CO2. El mayor crecimiento de la vegetación por el calentamiento climático desempeña un papel fundamental en la amplificación del ciclo estacional del CO2 atmosférico en las tierras del norte (>50° N) desde la década de 1960. Sin embargo, la correlación entre el crecimiento de la vegetación, la temperatura y la amplitud estacional de la concentración atmosférica de CO2 se ha vuelto difícil de alcanzar con la tendencia creciente lenta del crecimiento de la vegetación y el control debilitado de la temperatura en la absorción de CO2 desde finales de la década de 1990. Aquí, con base en los registros de concentración de CO2 atmosférico in situ del sitio del observatorio de Barrow, encontramos una desaceleración en la tendencia creciente de la amplitud del CO2 atmosférico desde la década de 1990 hasta mediados de la década de 2000. Este fenómeno se asoció con la disminución pausada de la concentración mínima de CO2 ([CO2]min), que se correlacionó significativamente con la desaceleración del reverdecimiento de la vegetación y la extensión de la duración de la temporada de crecimiento. Luego demostramos que tanto el verdor de la vegetación como la duración de la temporada de crecimiento se correlacionaban positivamente con la temperatura de primavera pero no de otoño en las tierras del norte. Además, tales dependencias asimétricas del crecimiento de la vegetación en la temperatura de primavera y otoño no pueden ser capturadas por los modelos de biosfera terrestre de última generación. Estos hallazgos indican que las respuestas del crecimiento de la vegetación al calentamiento de primavera y otoño son asimétricas, y resaltan la necesidad de mejorar la fenología del otoño en los modelos para predecir el ciclo estacional de la concentración atmosférica de CO2. The enhanced vegetation growth by climate warming plays a pivotal role in amplifying the seasonal cycle of atmospheric CO2 at northern lands (>50° N) since 1960s. However, the correlation between vegetation growth, temperature and seasonal amplitude of atmospheric CO2 concentration have become elusive with the slowed increasing trend of vegetation growth and weakened temperature control on CO2 uptake since late 1990s. Here, based on in situ atmospheric CO2 concentration records from the Barrow observatory site, we found a slowdown in the increasing trend of the atmospheric CO2 amplitude from 1990s to mid-2000s. This phenomenon was associated with the paused decrease in the minimum CO2 concentration ([CO2]min), which was significantly correlated with the slowdown of vegetation greening and growing-season length extension. We then showed that both the vegetation greenness and growing-season length were positively correlated with spring but not autumn temperature over the northern lands. Furthermore, such asymmetric dependences of vegetation growth upon spring and autumn temperature cannot be captured by the state-of-art terrestrial biosphere models. These findings indicate that the responses of vegetation growth to spring and autumn warming are asymmetric, and highlight the need of improving autumn phenology in the models for predicting seasonal cycle of atmospheric CO2 concentration. يلعب نمو الغطاء النباتي المعزز بسبب الاحترار المناخي دورًا محوريًا في تضخيم الدورة الموسمية لثاني أكسيد الكربون في الغلاف الجوي في الأراضي الشمالية (>50درجة شمالًا) منذ الستينيات. ومع ذلك، فإن العلاقة بين نمو الغطاء النباتي ودرجة الحرارة والسعة الموسمية لتركيز ثاني أكسيد الكربون في الغلاف الجوي أصبحت بعيدة المنال مع تباطؤ الاتجاه المتزايد لنمو الغطاء النباتي وضعف التحكم في درجة الحرارة عند امتصاص ثاني أكسيد الكربون منذ أواخر التسعينيات. هنا، بناءً على سجلات تركيز ثاني أكسيد الكربون في الغلاف الجوي في الموقع من موقع مرصد بارو، وجدنا تباطؤًا في الاتجاه المتزايد لسعة ثاني أكسيد الكربون في الغلاف الجوي من التسعينيات إلى منتصف العقد الأول من القرن الحادي والعشرين. ارتبطت هذه الظاهرة بالانخفاض المتوقف مؤقتًا في الحد الأدنى لتركيز ثاني أكسيد الكربون ([CO2]min)، والذي ارتبط بشكل كبير بتباطؤ تخضير الغطاء النباتي وتمديد طول موسم النمو. ثم أظهرنا أن كل من خضرة الغطاء النباتي وطول موسم النمو كانا مرتبطين بشكل إيجابي مع درجة حرارة الربيع ولكن ليس الخريف على الأراضي الشمالية. علاوة على ذلك، لا يمكن التقاط الاعتمادات غير المتماثلة لنمو الغطاء النباتي على درجة حرارة الربيع والخريف من خلال نماذج المحيط الحيوي الأرضية الحديثة. تشير هذه النتائج إلى أن استجابات نمو الغطاء النباتي لارتفاع درجة حرارة الربيع والخريف غير متماثلة، وتسلط الضوء على الحاجة إلى تحسين فينولوجيا الخريف في نماذج التنبؤ بالدورة الموسمية لتركيز ثاني أكسيد الكربون في الغلاف الجوي.

We present an approach to estimate the feedback from large-scale thawing of permafrost soils using a simplified, data-constrained model that combines three elements: soil carbon (C) maps and profiles to identify the distribution and type of C in permafrost soils; incubation experiments to quantify the rates of C lost after thaw; and models of soil thermal dynamics in response to climate warming. We call the approach the Permafrost Carbon Network Incubation–Panarctic Thermal scaling approach (PInc-PanTher). The approach assumes that C stocks do not decompose at all when frozen, but once thawed follow set decomposition trajectories as a function of soil temperature. The trajectories are determined according to a three-pool decomposition model fitted to incubation data using parameters specific to soil horizon types. We calculate litterfall C inputs required to maintain steady-state C balance for the current climate, and hold those inputs constant. Soil temperatures are taken from the soil thermal modules of ecosystem model simulations forced by a common set of future climate change anomalies under two warming scenarios over the period 2010 to 2100. Under a medium warming scenario (RCP4.5), the approach projects permafrost soil C losses of 12.2–33.4 Pg C; under a high warming scenario (RCP8.5), the approach projects C losses of 27.9–112.6 Pg C. Projected C losses are roughly linearly proportional to global temperature changes across the two scenarios. These results indicate a global sensitivity of frozen soil C to climate change (γsensitivity) of −14 to −19 Pg C °C−1on a 100 year time scale. For CH4emissions, our approach assumes a fixed saturated area and that increases in CH4emissions are related to increased heterotrophic respiration in anoxic soil, yielding CH4emission increases of 7% and 35% for the RCP4.5 and RCP8.5 scenarios, respectively, which add an additional greenhouse gas forcing of approximately 10–18%. The simplified approach presented here neglects many important processes that may amplify or mitigate C release from permafrost soils, but serves as a data-constrained estimate on the forced, large-scale permafrost C response to warming.

We present the global general circulation model IPSL-CM5 developed to study the long-term response of the climate system to natural and anthropogenic forcings as part of the 5th Phase of the Coupled Model Intercomparison Project (CMIP5). This model includes an interactive carbon cycle, a representation of tropospheric and stratospheric chemistry, and a comprehensive representation of aerosols. As it represents the principal dynamical, physical, and bio-geochemical processes relevant to the climate system, it may be referred to as an Earth System Model. However, the IPSL-CM5 model may be used in a multitude of configurations associated with different boundary conditions and with a range of complexities in terms of processes and interactions. This paper presents an overview of the different model components and explains how they were coupled and used to simulate historical climate changes over the past 150 years and different scenarios of future climate change. A single version of the IPSL-CM5 model (IPSL-CM5A-LR) was used to provide climate projections associated with different socio-economic scenarios, including the different Representative Concentration Pathways considered by CMIP5 and several scenarios from the Special Report on Emission Scenarios considered by CMIP3. Results suggest that the magnitude of global warming projections primarily depends on the socio-economic scenario considered, that there is potential for an aggressive mitigation policy to limit global warming to about two degrees, and that the behavior of some components of the climate system such as the Arctic sea ice and the Atlantic Meridional Overturning Circulation may change drastically by the end of the twenty-first century in the case of a no climate policy scenario. Although the magnitude of regional temperature and precipitation changes depends fairly linearly on the magnitude of the projected global warming (and thus on the scenario considered), the geographical pattern of these changes is strikingly similar for the different scenarios. The representation of atmospheric physical processes in the model is shown to strongly influence the simulated climate variability and both the magnitude and pattern of the projected climate changes.

Project: GCOS Earth Heat Inventory - A study under the Global Climate Observing System (GCOS) concerted international effort to update the Earth heat inventory (EHI), and presents an updated international assessment of ocean warming estimates, and new and updated estimates of heat gain in the atmosphere, cryosphere and land over the period from 1960 to present. Summary: The file “GCOS_EHI_1960-2020_Permafrost_Heat_Content_data.nc” presents the first estimate of permafrost heat storage within the Arctic region for the period 1960-2020. A perturbed parameter ensemble of simulations using the CryoGridLite permafrost model and climate forcings from the ERA-Interim reanalysis (1979-2020) and the Mk3L climate system model (500 CE -1979) allow to estimate the latent heat flux due to phase change in the subsurface from the surface to 550 m of depth. This ensemble of simulations allows to retrieve the uncertainty due to the unknown distribution of ground ice in the Arctic. More info: ESSOAr preprint server, https://doi.org/10.1002/essoar.10511600.1. The data are described in Nitzbon et al. (2022), and used in von Schuckmann et al. (2022).

Project: IPCC Data Distribution Centre : Supplementary data sets for the Sixth Assessment Report - For the Sixth Assessment Report of the IPCC (AR6) input/source and intermediate datasets underlying the AR6 were collected and long-term archived. This project compliments CMIP6 data subset and snapshot analyzed for the WGI AR6. Summary: This data set contains detailed elements the sea level projections associated with the Intergovernmental Panel on Climate Change Sixth Assessment Report. In particular, it contains relative sea level projection distributions for all the workflows described in AR6 WGI 9.6.3.2, as well as distributions for the components contributing to relative sea level change. These data may be of use for users who want to substitute their own estimates. Regional projections can also be accessed through the NASA/IPCC Sea Level Projections Tool at https://sealevel.nasa.gov/ipcc-ar6-sea-level-projection-tool. See https://zenodo.org/communities/ipcc-ar6-sea-level-projections for additional related data sets.