• Energy Research

Changing atmospheric composition due to human activities, primarily carbon dioxide (CO2) emissions from fossil fuel burning, is already impacting ocean circulation, biogeochemistry, and ecology, and model projections indicate that observed trends will continue or even accelerate over this century. Elevated atmospheric CO2 alters Earth's radiative balance, leading to global-scale warming and climate change. The ocean stores the majority of resulting anomalous heat, which in turn drives other physical, chemical, and biological impacts. Sea surface warming and increased ocean vertical stratification are projected to reduce global-integrated primary production and export flux as well as to lower subsurface dissolved oxygen concentrations. Upper trophic levels will be affected both directly by warming and indirectly from changes in productivity and expanding low oxygen zones. The ocean also absorbs roughly one-quarter of present-day anthropogenic CO2 emissions. The resulting changes in seawater chemistry, termed ocean acidification, include declining pH and saturation state for calcium carbon minerals that may have widespread impacts on many marine organisms. Climate warming will likely slow ocean CO2 uptake but is not expected to significantly reduce upper ocean acidification. Improving the accuracy of future model projections requires better observational constraints on current rates of ocean change and a better understanding of the mechanisms controlling key physical and biogeochemical processes.

Résumé. Un système d'observation et d'analyse du carbone intégré à l'échelle mondiale est nécessaire pour améliorer la compréhension fondamentale du cycle mondial du carbone, pour améliorer notre capacité à projeter les changements futurs et pour vérifier l'efficacité des politiques visant à réduire les émissions de gaz à effet de serre et à augmenter la séquestration du carbone. La construction d'un système intégré d'observation du carbone nécessite des avancées transformationnelles du cadre exploratoire clairsemé existant vers un système dense, robuste et durable dans toutes ses composantes : les émissions anthropiques, l'atmosphère, l'océan et la biosphère terrestre. L'objectif de cette étude est d'identifier l'état actuel des observations de carbone et les besoins d'un système mondial intégré d'observation du carbone qui peut être construit au cours de la prochaine décennie. Une conclusion clé est l'expansion substantielle (de plusieurs ordres de grandeur) des réseaux d'observation au sol nécessaires pour atteindre la haute résolution spatiale pour les flux de CO2 et de CH4 et pour les stocks de carbone afin de répondre aux objectifs politiques pertinents et d'attribuer les changements de flux aux processus sous-jacents dans chaque région. Afin d'établir des diagnostics de flux et de stocks sur des zones éloignées telles que les océans du sud, les forêts tropicales et l'Arctique, les observations in situ devront être complétées par des mesures de télédétection. La télédétection offre l'avantage d'une couverture spatiale dense et de revisites fréquentes. Un défi clé consiste à amener les mesures de télédétection à un niveau de cohérence et de précision à long terme afin qu'elles puissent être efficacement combinées dans des modèles pour réduire les incertitudes, en synergie avec les données au sol. Apporter des contraintes d'observation strictes sur les émissions de combustibles fossiles et de changement d'affectation des terres sera le plus grand défi pour le déploiement d'un système intégré d'observation du carbone pertinent pour les politiques. Cela nécessitera des données in situ et de télédétection à une résolution et une densité beaucoup plus élevées que celles actuellement atteintes pour les flux naturels, bien que sur une petite superficie (villes, sites industriels, centrales électriques), ainsi que l'inclusion de mesures indirectes de CO2 de combustibles fossiles telles que le radiocarbone dans les traceurs de combustion de CO2 et de carbone. En outre, un système de surveillance du carbone pertinent pour les politiques devrait également fournir des mécanismes pour concilier les estimations des flux régionaux descendants (basés sur l'atmosphère) et ascendants (basés sur la surface) sur toute la gamme des échelles spatiales et temporelles pertinentes pour les politiques d'atténuation. Le succès du système reposera sur des engagements à long terme en matière de suivi, sur une meilleure collaboration internationale pour combler les lacunes dans les observations actuelles, sur des efforts soutenus pour améliorer l'accès aux différents flux de données et rendre les bases de données interopérables, et sur l'étalonnage de chaque composante du système à des échelles internationales convenues. Resumen. Se necesita un sistema de observación y análisis de carbono integrado a nivel mundial para mejorar la comprensión fundamental del ciclo global del carbono, para mejorar nuestra capacidad de proyectar cambios futuros y para verificar la efectividad de las políticas destinadas a reducir las emisiones de gases de efecto invernadero y aumentar el secuestro de carbono. Construir un sistema integrado de observación de carbono requiere avances transformacionales desde el marco exploratorio escaso existente hacia un sistema denso, robusto y sostenido en todos los componentes: las emisiones antropogénicas, la atmósfera, el océano y la biosfera terrestre. El objetivo de este estudio es identificar el estado actual de las emisiones de carbono y las necesidades de un sistema global integrado de emisiones de carbono que pueda construirse en la próxima década. Una conclusión clave es la expansión sustancial (en varios órdenes de magnitud) de las redes de observación terrestres necesarias para alcanzar la alta resolución espacial para los flujos de CO2 y CH4, y para las reservas de carbono para abordar los objetivos relevantes para las políticas y atribuir los cambios de flujo a los procesos subyacentes en cada región. Para establecer diagnósticos de flujo y stock en áreas remotas como los océanos del sur, los bosques tropicales y el Ártico, las observaciones in situ deberán complementarse con mediciones de teledetección. La teledetección ofrece la ventaja de una cobertura espacial densa y una revisión frecuente. Un desafío clave es llevar las mediciones de teledetección a un nivel de consistencia y precisión a largo plazo para que puedan combinarse de manera eficiente en modelos para reducir las incertidumbres, en sinergia con los datos basados en tierra. Traer restricciones observacionales estrictas sobre las emisiones de combustibles fósiles y el cambio en el uso de la tierra será el mayor desafío para el despliegue de un sistema integrado de observación de carbono relevante para las políticas. Esto requerirá datos in situ y teledetectados con una resolución y densidad mucho más altas que las que se logran actualmente para los flujos naturales, aunque en una pequeña superficie de tierra (ciudades, sitios industriales, centrales eléctricas), así como la inclusión de mediciones indirectas de CO2 de combustibles fósiles, como el radiocarbono en CO2 y los trazadores de combustión de combustibles de carbono. Además, un sistema de monitoreo de carbono relevante para las políticas también debe proporcionar mecanismos para conciliar las estimaciones regionales de flujo de arriba hacia abajo (basadas en la atmósfera) y de abajo hacia arriba (basadas en la superficie) en toda la gama de escalas espaciales y temporales relevantes para las políticas de mitigación. El éxito del sistema dependerá de los compromisos a largo plazo con el monitoreo, de una mejor colaboración internacional para llenar los vacíos en las observaciones actuales, de esfuerzos sostenidos para mejorar el acceso a los diferentes flujos de datos y hacer que las bases de datos sean interoperables, y de la calibración de cada componente del sistema a escalas internacionales acordadas. Abstract. A globally integrated carbon observation and analysis system is needed to improve the fundamental understanding of the global carbon cycle, to improve our ability to project future changes, and to verify the effectiveness of policies aiming to reduce greenhouse gas emissions and increase carbon sequestration. Building an integrated carbon observation system requires transformational advances from the existing sparse, exploratory framework towards a dense, robust, and sustained system in all components: anthropogenic emissions, the atmosphere, the ocean, and the terrestrial biosphere. The goal of this study is to identify the current state of carbon observations and needs for a global integrated carbon observation system that can be built in the next decade. A key conclusion is the substantial expansion (by several orders of magnitude) of the ground-based observation networks required to reach the high spatial resolution for CO2 and CH4 fluxes, and for carbon stocks for addressing policy relevant objectives, and attributing flux changes to underlying processes in each region. In order to establish flux and stock diagnostics over remote areas such as the southern oceans, tropical forests and the Arctic, in situ observations will have to be complemented with remote-sensing measurements. Remote sensing offers the advantage of dense spatial coverage and frequent revisit. A key challenge is to bring remote sensing measurements to a level of long-term consistency and accuracy so that they can be efficiently combined in models to reduce uncertainties, in synergy with ground-based data. Bringing tight observational constraints on fossil fuel and land use change emissions will be the biggest challenge for deployment of a policy-relevant integrated carbon observation system. This will require in-situ and remotely sensed data at much higher resolution and density than currently achieved for natural fluxes, although over a small land area (cities, industrial sites, power plants), as well as the inclusion of fossil fuel CO2 proxy measurements such as radiocarbon in CO2 and carbon-fuel combustion tracers. Additionally, a policy relevant carbon monitoring system should also provide mechanisms for reconciling regional top-down (atmosphere-based) and bottom-up (surface-based) flux estimates across the range of spatial and temporal scales relevant to mitigation policies. The success of the system will rely on long-term commitments to monitoring, on improved international collaboration to fill gaps in the current observations, on sustained efforts to improve access to the different data streams and make databases inter-operable, and on the calibration of each component of the system to agreed-upon international scales. الخلاصة. هناك حاجة إلى نظام متكامل عالميًا لمراقبة الكربون وتحليله لتحسين الفهم الأساسي لدورة الكربون العالمية، وتحسين قدرتنا على توقع التغييرات المستقبلية، والتحقق من فعالية السياسات التي تهدف إلى الحد من انبعاثات غازات الدفيئة وزيادة عزل الكربون. يتطلب بناء نظام متكامل لمراقبة الكربون تقدمًا تحويليًا من الإطار الاستكشافي المتناثر الحالي نحو نظام كثيف وقوي ومستدام في جميع المكونات: الانبعاثات البشرية المنشأ والغلاف الجوي والمحيطات والمحيط الحيوي الأرضي. الهدف من هذه الدراسة هو تحديد الوضع الحالي لملاحظات الكربون والاحتياجات لنظام عالمي متكامل لمراقبة الكربون يمكن بناؤه في العقد المقبل. الاستنتاج الرئيسي هو التوسع الكبير (بعدة مرات من حيث الحجم) لشبكات المراقبة الأرضية المطلوبة للوصول إلى الاستبانة المكانية العالية لتدفقات ثاني أكسيد الكربون والميثان، ولمخزونات الكربون لمعالجة الأهداف ذات الصلة بالسياسات، وعزو تغييرات التدفق إلى العمليات الأساسية في كل منطقة. من أجل إنشاء تشخيصات التدفق والأرصدة في المناطق النائية مثل المحيطات الجنوبية والغابات الاستوائية والقطب الشمالي، يجب استكمال الملاحظات في الموقع بقياسات الاستشعار عن بعد. يوفر الاستشعار عن بعد ميزة التغطية المكانية الكثيفة وإعادة الزيارة المتكررة. ويتمثل أحد التحديات الرئيسية في الوصول بقياسات الاستشعار عن بعد إلى مستوى من الاتساق والدقة على المدى الطويل بحيث يمكن دمجها بكفاءة في نماذج للحد من أوجه عدم اليقين، بالتآزر مع البيانات الأرضية. سيكون فرض قيود صارمة على مراقبة الوقود الأحفوري وانبعاثات تغير استخدام الأراضي هو التحدي الأكبر أمام نشر نظام متكامل لمراقبة الكربون ذي صلة بالسياسات. وسيتطلب ذلك بيانات في الموقع ومستشعرة عن بعد بدقة وكثافة أعلى بكثير مما هو متحقق حاليًا للتدفقات الطبيعية، على الرغم من أنها على مساحة أرض صغيرة (المدن والمواقع الصناعية ومحطات الطاقة)، بالإضافة إلى تضمين قياسات وكيل ثاني أكسيد الكربون للوقود الأحفوري مثل الكربون المشع في ثاني أكسيد الكربون وتتبع احتراق الوقود الكربوني. بالإضافة إلى ذلك، يجب أن يوفر نظام رصد الكربون ذي الصلة بالسياسة أيضًا آليات للتوفيق بين تقديرات التدفق الإقليمية من أعلى إلى أسفل (القائمة على الغلاف الجوي) ومن أسفل إلى أعلى (السطحية) عبر نطاق المقاييس المكانية والزمنية ذات الصلة بسياسات التخفيف. سيعتمد نجاح النظام على الالتزامات طويلة الأجل بالرصد، وعلى تحسين التعاون الدولي لسد الثغرات في الملاحظات الحالية، وعلى الجهود المستمرة لتحسين الوصول إلى تدفقات البيانات المختلفة وجعل قواعد البيانات قابلة للتشغيل المتبادل، وعلى معايرة كل مكون من مكونات النظام وفقًا للنطاقات الدولية المتفق عليها.

For each assessment cycle of the Intergovernmental Panel on Climate Change (IPCC), researchers in the life sciences are called upon to provide evidence to policymakers planning for a changing future. This research increasingly relies on highly technical and complex outputs from climate models. The strengths and weaknesses of these data may not be fully appreciated beyond the climate modelling community; therefore, uninformed use of raw or preprocessed climate data could lead to overconfident or spurious conclusions. We provide an accessible introduction to climate model outputs that is intended to empower the life science community to robustly address questions about human and natural systems in a changing world.

AbstractClimate‐induced changes in the physical, chemical, and biological environment are expected to increasingly stress marine ecosystems, with important consequences for fisheries exploitation. Here, we use the APECOSM‐E numerical model (Apex Predator ECOSystem Model ‐ Estimation) to evaluate the future impacts of climate change on the physiology, spatial distribution, and abundance of skipjack tuna, the worldwide most fished species of tropical tuna. The main novelties of our approach lie in the mechanistic link between environmental factors, metabolic rates, and behavioral responses and in the fully three dimensional representation of habitat and population abundance. Physical and biogeochemical fields used to force the model are provided by the last generation of the IPSL‐CM5 Earth System Model run from 1990 to 2100 under a ‘business‐as‐usual’ scenario (RCP8.5). Our simulations show significant changes in the spatial distribution of skipjack tuna suitable habitat, as well as in their population abundance. The model projects deterioration of skipjack habitat in most tropical waters and an improvement of habitat at higher latitudes. The primary driver of habitat changes is ocean warming, followed by food density changes. Our projections show an increase of global skipjack biomass between 2010 and 2050 followed by a marked decrease between 2050 and 2095. Spawning rates are consistent with population trends, showing that spawning depends primarily on the adult biomass. On the other hand, growth rates display very smooth temporal changes, suggesting that the ability of skipjack to keep high metabolic rates in the changing environment is generally effective. Uncertainties related to our model spatial resolution, to the lack or simplification of key processes and to the climate forcings are discussed.

The national climate action plans to cut greenhouse gas emissions, referred to as Nationally Determined Contributions (NDCs), currently include anthropogenic land-based carbon fluxes but typically exclude open ocean carbon sinks within Exclusive Economic Zones (EEZs). Here, we utilise a high-resolution global ocean biogeochemical model alongside available observations to illustrate why including EEZ carbon sinks in NDCs would be both conceptually and practically highly problematic.To demonstrate this, we focus on the case of the French EEZ, where we simulate an anthropogenic carbon sink of 0.21 GtCO2·yr–1 over the past decade, representing nearly 50% of France’s territorial greenhouse gas emissions over the same period. However, it should be noted that this anthropogenic carbon uptake results from the physical and biogeochemical properties of water masses, rather than from human management practices. Additionally, the EEZ oceanic carbon sink is already considered in estimates of remaining carbon budgets to meet the goals of the Paris Agreement. Therefore, integrating these fluxes into NDCs would lead to inconsistency between national objectives and global climate goals.We argue that to identify the additionality of management measures aimed at enhancing the anthropogenic carbon sink in EEZ waters, robust assessments of the baseline carbon sink and how it would have evolved without intervention will be needed. As we show, this is complicated by the spatially and temporally dynamic nature of ocean carbon fluxes. More fundamentally, there is no colocalization between air–sea fluxes and the subsequent sequestration of carbon in the ocean due to circulation and mixing. Consequently, the measurement, reporting, and verification requirements for national stocktakes would be highly challenging. Moreover, as fluxes predominantly occur in the high latitude oceans and sequestration in the subtropics, the national allocation of credits would involve contentious issues of equity and justice.

Abstract Background Ocean-related options (OROs) to mitigate and adapt to climate change are receiving increasing attention from practitioners, decision-makers, and researchers. In order to guide future ORO development and implementation, a catalogue of scientific evidence addressing outcomes related to different ORO types is critical. However, until now, such a synthesis has been hindered by the large size of the evidence base. Here, we detail a protocol using a machine learning-based approach to systematically map the extent and distribution of academic evidence relevant to the development, implementation, and outcomes of OROs. Method To produce this systematic map, literature searches will be conducted in English across two bibliographic databases using a string of search terms relating to the ocean, climate change, and OROs. A sample of articles from the resulting de-duplicated corpus will be manually screened at the title and abstract level for inclusion or exclusion against a set of predefined eligibility criteria in order to select all relevant literature on marine and coastal socio-ecological systems, the type of ORO and its outcomes. Descriptive metadata on the type and location of intervention, study methodology, and outcomes will be coded from the included articles in the sample. This sample of screening and coding decisions will be used to train a machine learning model that will be used to estimate these labels for all the remaining unseen publications. The results will be reported in a narrative synthesis summarising key trends, knowledge gaps, and knowledge clusters.

The Paris Agreement target of limiting global surface warming to 1.5-2°C compared to pre-industrial levels by 2100 will still heavily impact the ocean. While ambitious mitigation and adaptation are both needed, the ocean provides major opportunities for action to reduce climate change globally and its impacts on vital ecosystems and ecosystem services. A comprehensive and systematic assessment of 13 global- and local-scale, ocean-based measures was performed to help steer the development and implementation of technologies and actions toward a sustainable outcome. We show that (1) all measures have tradeoffs and multiple criteria must be used for a comprehensive assessment of their potential, (2) greatest benefit is derived by combining global and local solutions, some of which could be implemented or scaled-up immediately, (3) some measures are too uncertain to be recommended yet, (4) political consistency must be achieved through effective cross-scale governance mechanisms, (5) scientific effort must focus on effectiveness, co-benefits, disbenefits, and costs of poorly tested as well as new and emerging measures.