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Nitrogen (N) and phosphorus (P) biogeochemical dynamics are crucial for the regulation of the terrestrial carbon cycle. In Earth system models (ESMs) the implementation of nutrient limitations has been shown to improve the carbon cycle feedback representation and, hence, the fidelity of the response of land to simulated atmospheric CO2 rise. Here we aimed to implement a terrestrial N and P cycle in an Earth system model of intermediate complexity to improve projections of future CO2 fertilization feedbacks. The N cycle is an improved version of the Wania et al. (2012) N module, with enforcement of N mass conservation and the merger with a deep land-surface and wetland module that allows for the estimation of N2O and NO fluxes. The N cycle module estimates fluxes from three organic (litter, soil organic matter and vegetation) and two inorganic (NH4+ and NO3-) pools and accounts for inputs from biological N fixation and N deposition. The P cycle module contains the same organic pools with one inorganic P pool; it estimates influx of P from rock weathering and losses from leaching and occlusion. Two historical simulations are carried out for the different nutrient limitation setups of the model: carbon and nitrogen (CN), as well as carbon, nitrogen and phosphorus (CNP), with a baseline carbon-only simulation. The improved N cycle module now conserves mass, and the added fluxes (NO and N2O), along with the N and P pools, are within the range of other studies and literature. For the years 2001–2015 the nutrient limitation resulted in a reduction of gross primary productivity (GPP) from the carbon-only value of 143 to 130 Pg C yr−1 in the CN version and 127 Pg C yr−1 in the CNP version. This implies that the model efficiently represents a nutrient limitation over the CO2 fertilization effect. CNP simulation resulted in a reduction of 11 % of the mean GPP and a reduction of 23 % of the vegetation biomass compared to the baseline C simulation. These results are in better agreement with observations, particularly in tropical regions where P limitation is known to be important. In summary, the implementation of the N and P cycle has successfully enforced a nutrient limitation in the terrestrial system, which has now reduced the primary productivity and the capacity of land to take up atmospheric carbon, better matching observations.

promet, 105, Beitrag 9

Das Ergebnispapier ist das Resultat des IdeenLaufs im Wissenschaftsjahr 2022 – Nachgefragt!. Es ist das Ergebnis des Austauschs zwischen Wissenschaft und Gesellschaft sowie zwischen vielen verschiedenen wissenschaftlichen Disziplinen. Bürger*innen in ganz Deutschland waren beim IdeenLauf unter dem Motto #MeineFragefürdieWissenschaft eingeladen, Fragen für die Wissenschaft einzureichen. Über 14.000 Fragen haben die Menschen als Reaktion auf den Aufruf gestellt. Entstanden ist daraus dieses Ergebnispapier. In die 59 Cluster und 9 ZukunftsRäume sind eine Vielzahl von Fragen, individuellen Interessen und Lebensrealitäten von vielen Menschen eingeflossen. Das Papier soll als Ideenpool und Anregung für zukünftige Forschungsvorhaben und Forschungspolitik dienen

The Net-Zero-2050 cluster aims for a national roadmap for net zero CO2 emissions by 2050, including integrated scenario analyses and negative emission technology assessment (see fact sheet Net-Zero-2050 Structure Project 1). This national target to substantially reduce national CO2 emissions by 2050 stems from the objective to comply with the global long-term temperature goal of well below 2°C of the Paris Agreement (UNFCCC, 2015). Within the cluster it is therefore important to decide on an approach for deriving a national remaining carbon budget from global emissions trajectories in agreement with the Paris Climate Agreement’s longterm temperature goal (UNFCCC, 2015). Allocating national carbon budgets is a balance of environmental effectiveness, equity, national capacity and ability, political feasibility, economic efficiency and technical requirements (Gignac and Matthews, 2015; Höhne et al., 2003; 2014). Given Germany’s capacity and abilities, we decided to follow a sustainable growth trajectory with a convergence phase to equal-per-capita CO2 emissions by 2035, and a net zero CO2 emissions trajectory after 2050 until the end of the century. This approach leads to a remaining Germany CO2 budget of 9 GtCO2 (from 1st January 2018 to 2050 and 2100), which we propose to be used across the Net-Zero-2050 cluster. The remaining carbon budget will serve as a target to be used in all work packages in a concerted way, either qualitatively or quantitatively, and in accordance with other work packages (see also fact sheet Net-Zero-2050 Energy Scenario Approach). The calculated budget is at the lower end of the national budget if allocated by the grandfathering approach (emissions are allocated with respect to today’s emissions shares: 5.5-13.1 GtCO2), but slightly higher than the highest estimate of an equal-per-capita remaining carbon budget (emissions are allocated with respect to Germany’s share of the global population: 3.5-8.4 GtCO2) The 9 GtCO2 national remaining CO2 budget, 6.9 GtCO2 from 1st January 2021, will need to be broken down by category (e.g. energy, land use, industrial processes, and man-made sinks and sources; see Gap Analysis Report) in order to provide a consistent approach across work packages.

The energy system transformation in Germany is a challenge for society, economy and politics and has several impacts on multiple scales. This paper investigates the effects of the trajectories towards net zero emissions by 2050 through focusing on the spatial dimension of impacts, benefits, and losses for different stakeholders and technologies. Spatial heterogeneity in the energy transition means that regions enjoying benefits from decarbonization might diverge from regions experiencing losses, and that there are different geographical potentials and challenges. The question arising is one of the need for redistribution between benefits and losses, whilst ensuring that all stakeholders remain willing to act as frontrunners in the transformation of the energy system. Inclusion and participation in the process, together with a carefully targeted mixed set of regional energy policy, combining tax solutions and incentives for acceptance of required measures could facilitate a successful, efficient policy-supported energy transition.

Non-technical summary. We summarize some of the past year’s most important findings within climate change-related research. New research has improved our understanding about the remaining options to achieve the Paris Agreement goals, through overcoming political barriers to carbon pricing, taking into account non-CO2 factors, a well-designed implementation of demand-side and nature-based solutions, resilience building of ecosystems and the recognition that climate change mitigation costs can be justified by benefits to the health of humans and nature alone. We consider new insights about what to expect if we fail to include a new dimension of fire extremes and the prospect of cascading climate tipping elements. Technical summary. A synthesis is made of 10 topics within cli- mate research, where there have been significant advances since January 2020. The insights are based on input from an inter- national open call with broad disciplinary scope. Findings include: (1) the options to still keep global warming below 1.5 °C; (2) the impact of non-CO2 factors in global warming; (3) a new dimension of fire extremes forced by climate change; (4) the increasing pressure on interconnected climate tipping elements; (5) the dimensions of climate justice; (6) political chal- lenges impeding the effectiveness of carbon pricing; (7) demand- side solutions as vehicles of climate mitigation; (8) the potentials and caveats of nature-based solutions; (9) how building resili- ence of marine ecosystems is possible; and (10) that the costs of climate change mitigation policies can be more than justified by the benefits to the health of humans and nature. Social media summary. How dowe limit global warming to 1.5 °C and why is it crucial? See highlights of latest climate science. Objectius de Desenvolupament Sostenible::8 - Treball Decent i Creixement Econòmic::8.4 - Millorar progressivament, per a 2030, la producció i el consum eficients dels recursos mundials i procurar desvincular el creixement econòmic de la degradació del medi ambient, de conformitat amb el Marc decennal de programes sobre modalitats sostenibles de consum i producció, començant pels països desenvolupats Objectius de Desenvolupament Sostenible::10 - Reducció de les Desigualtats Objectius de Desenvolupament Sostenible::13 - Acció per al Clima Objectius de Desenvolupament Sostenible::17 - Aliança per a Aconseguir els Objetius Objectius de Desenvolupament Sostenible::14 - Vida Submarina Objectius de Desenvolupament Sostenible::15 - Vida d'Ecosistemes Terrestres Objectius de Desenvolupament Sostenible::16 - Pau, Justícia i Institucions Sòlides

This is the fifth instalmentfrom the annual series10 New Insights in Climate Science, whichaims to synthesise and communicate the latest and most essential scientific findings on climate change. It is the result of a collaboration between Future Earth,Earth League and the World Climate Research Program (WCRP). Thisreport constitutes a climate science year-in-review for journalists, policy makers, and the general public. A peer-reviewed academic article published in parallel to this policy report, providesanin-depth explanationof the ten insights,as well as a complete account of the reviewing process. These are the 2021ten New Insights in Climate Science: Stabilizing at 1.5°C warming is still possible, but immediate and drastic global action is required. Rapid growth in methane and nitrous oxide emissions put us on track for 2.7°C warming Megafires – climate change forces fire extremes to reach new dimensions with extreme impacts Climate tipping elements incur high-impact risks Global climate action must be just Supporting household behaviour changes is a crucial but often overlooked opportunity for climate action Political challenges impede effectiveness of carbon pricing Nature-based solutions are critical for the pathway to Paris – but look at the fine print Building resilience of marine ecosystems is achievable by climate-adapted conservation and management, and global stewardship Costs of climate change mitigation can be justified by the multiple immediate benefits to the health of humans and nature

Greenhouse gas emissions and air pollution have changed the composition of the atmosphere, and thereby initiated global warming and reduced air quality. Our editorial board members note the need for a deeper understanding of atmospheric fluxes and processes to tackle climate and human health issues.

The University of Victoria Earth System Climate Model (UVic ESCM) of intermediate complexity has been a useful tool in recent assessments of long-term climate changes, including both paleo-climate modelling and uncertainty assessments of future warming. Since the last official release of the UVic ESCM 2.9 and the two official updates during the last decade, considerable model development has taken place among multiple research groups. The new version 2.10 of the University of Victoria Earth System Climate Model presented here will be part of the sixth phase of the Coupled Model Intercomparison Project (CMIP6). More precisely it will be used in the intercomparison of Earth system models of intermediate complexity (EMIC), such as the C4MIP, the Carbon Dioxide Removal and Zero Emissions Commitment model intercomparison projects (CDR-MIP and ZECMIP, respectively). It now brings together and combines multiple model developments and new components that have come about since the last official release of the model. The main additions to the base model are (i) an improved biogeochemistry module for the ocean, (ii) a vertically resolved soil model including dynamic hydrology and soil carbon processes, and (iii) a representation of permafrost carbon. To set the foundation of its use, we here describe the UVic ESCM 2.10 and evaluate results from transient historical simulations against observational data. We find that the UVic ESCM 2.10 is capable of reproducing changes in historical temperature and carbon fluxes well. The spatial distribution of many ocean tracers, including temperature, salinity, phosphate and nitrate, also agree well with observed tracer profiles. The good performance in the ocean tracers is connected to an improved representation of ocean physical properties. For the moment, the main biases that remain are a vegetation carbon density that is too high in the tropics, a higher than observed change in the ocean heat content (OHC) and an oxygen utilization in the Southern Ocean that is too low. All of these biases will be addressed in the next updates to the model.

The interdisciplinary exchange in climate engineering research offers a unique opportunity to make assumptions more explicit for such research projects. While making assumptions explicit is the standard in all disciplinary sciences, some assumptions in the context of societal challenges can only be usefully unveiled, discussed, and verified from the perspective of other research disciplines. Results from successful interdisciplinary collaborations are then more accessible and more generalizable to actors beyond the confines of the academic community. We aim to illustrate how interdisciplinary exchange helps to unveil assumptions in research endeavors and why this is important for successful interdisciplinary collaborations. We therefore follow different stages of the German Priority Program on Climate Engineering (SPP 1689), which we use as an example case of a successful interdisciplinary project. SPP 1689 focused on risks, challenges, and opportunities of Climate Engineering from the perspectives of numerous disciplines. Major results were that the initial assessments of technologies had to be sobered, the consideration of trade-offs is crucial for the potential assessment, and governance issues appeared larger than previously considered. From the reflections of SPP 1689, we conclude with three lessons learned: (1) The project profited from egalitarian organizational structures and communicative practices, preventing the predominance from single disciplines. (2) Within the project continuous efforts were undertaken to foster interdisciplinary understanding. In addition, the flexible project structure allowed for the accommodation of research needs arising as a result of these exchanges. (3) SPP 1689 offered early career researchers a platform for professional exchange on common challenges and best practices of being a part of an interdisciplinary research project., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, Concordia University http://dx.doi.org/10.13039/501100002914, Simon Fraser University (CA), Bundesministerium für Bildung und Forschung http://dx.doi.org/10.13039/501100002347

The interdisciplinary exchange in climate engineering research offers a unique opportunity to make assumptions more explicit for such research projects. While making assumptions explicit is the standard in all disciplinary sciences, some assumptions in the context of societal challenges can only be usefully unveiled, discussed, and verified from the perspective of other research disciplines. Results from successful interdisciplinary collaborations are then more accessible and more generalizable to actors beyond the confines of the academic community. We aim to illustrate how interdisciplinary exchange helps to unveil assumptions in research endeavors and why this is important for successful interdisciplinary collaborations. We therefore follow different stages of the German Priority Program on Climate Engineering (SPP 1689), which we use as an example case of a successful interdisciplinary project. SPP 1689 focused on risks, challenges, and opportunities of Climate Engineering from the perspectives of numerous disciplines. Major results were that the initial assessments of technologies had to be sobered, the consideration of trade-offs is crucial for the potential assessment, and governance issues appeared larger than previously considered. From the reflections of SPP 1689, we conclude with three lessons learned: (1) The project profited from egalitarian organizational structures and communicative practices, preventing the predominance from single disciplines. (2) Within the project continuous efforts were undertaken to foster interdisciplinary understanding. In addition, the flexible project structure allowed for the accommodation of research needs arising as a result of these exchanges. (3) SPP 1689 offered early career researchers a platform for professional exchange on common challenges and best practices of being a part of an interdisciplinary research project.

The Zero Emissions Commitment (ZEC) is the change in global mean temperature expected to occur following the cessation of net CO2 emissions and as such is a critical parameter for calculating the remaining carbon budget. The Zero Emissions Commitment Model Intercomparison Project (ZECMIP) was established to gain a better understanding of the potential magnitude and sign of ZEC, in addition to the processes that underlie this metric. A total of 18 Earth system models of both full and intermediate complexity participated in ZECMIP. All models conducted an experiment where atmospheric CO2 concentration increases exponentially until 1000 PgC has been emitted. Thereafter emissions are set to zero and models are configured to allow free evolution of atmospheric CO2 concentration. Many models conducted additional second-priority simulations with different cumulative emission totals and an alternative idealized emissions pathway with a gradual transition to zero emissions. The inter-model range of ZEC 50 years after emissions cease for the 1000 PgC experiment is −0.36 to 0.29 ∘C, with a model ensemble mean of −0.07 ∘C, median of −0.05 ∘C, and standard deviation of 0.19 ∘C. Models exhibit a wide variety of behaviours after emissions cease, with some models continuing to warm for decades to millennia and others cooling substantially. Analysis shows that both the carbon uptake by the ocean and the terrestrial biosphere are important for counteracting the warming effect from the reduction in ocean heat uptake in the decades after emissions cease. This warming effect is difficult to constrain due to high uncertainty in the efficacy of ocean heat uptake. Overall, the most likely value of ZEC on multi-decadal timescales is close to zero, consistent with previous model experiments and simple theory.

The aim of this Project Briefing is a clear definition of the various dimensions of our scenario approach in Net-Zero-2050. Starting from the overarching framework, we then describe, how scenarios are applied in the various projects. We define the scope and focus of the energy scenarios and the scenarios for Carbon Dioxide Removal measures, as well as the interface between both approaches.

Net-Zero-2050 aims for a national roadmap for net-zero CO2 emissions by 2050, including integrated scenario analyses and negative emission technology assessment. The aim of this project briefing is to clarify the overall carbon budget available for Germany to comply with the global long-term temperature limit of well below 2°C of the Paris Agreement.

Clarification of the work focus and the connection of the different elements of the Helmholtz Climate Initiative‘s Cluster I Net-Zero-2050

Estimates of the 1.5°C carbon budget vary widely among recent studies. One key contribution to this range is the non-CO2 climate forcing scenario uncertainty. Based on a partitioning of historical non-CO2 forcing, we show that there is currently a net negative non-CO2 forcing from fossil fuel combustion (FFC) mainly due to the co-emission of aerosols, and a net positive non-CO2 climate forcing from land-use change (LUC) and agricultural activities. We then perform a set of future simulations in which we prescribed a 1.5°C temperature stabilization trajectory, and diagnosed the resulting 1.5°C carbon budgets. Using the results of our historical partitioning, we prescribed changing non-CO2 forcing scenarios that are consistent with our model’s simulated decrease in FFC CO2 emissions. We compared the diagnosed carbon budgets from these idealized scenarios to those resulting from the default RCP scenario non-CO2 forcing, as well as from a scenario in which we assumed proportionality between future CO2 and non-CO2 forcing. We find a large range of carbon budget estimates across scenarios, with the largest budget emerging from the scenario with assumed proportionality of CO2 and non-CO2 forcing. Furthermore, our adjusted-RCP scenarios, in which the non-CO2 forcing is consistent with model-diagnosed FFC CO2 emissions, produced carbon budgets that are smaller than the corresponding default RCP scenarios. Our results suggest that ambitious mitigation scenarios will likely be characterized by an increasing contribution of non-CO2 forcing, and that an assumption of continued proportionality between CO2 and non-CO2 forcing would lead to an overestimate of the remaining carbon budget required to avoid low-temperature targets. Maintaining such proportionality under ambitious fossil fuel mitigation would require mitigation of non-CO2 emissions from agriculture and other non-FFC sources at a rate that is substantially faster than is found in the standard RCP scenarios.

The transient climate response for cumulative CO2 emissions (TCRE) enables us to estimate the total allowable CO2 emissions associated with a given CO2-induced temperature target. However, for this metric to be applicable to calculate the remaining carbon budget for 'real world' observed temperature changes, it needs to take into account the considerable contribution of non-CO2 climate forcers. In recent work this metric has been extended to the concept of the "Effective TCRE," which attempts to represent a similar relationship between CO2-equivalent emissions and total anthropogenic warming. Here we show, that while in the historical period the net-forcing from non-CO2 forcing agents has been approximately proportional to CO2 forcing, it is problematic to assume a similar behaviour for future scenarios. We further show how different assumptions on future non-CO2 climate forcing impact the estimates of the remaining carbon budgets, focussing on the example of the 1.5ºC temperature target.

Selecting appropriate indicators is essential to aggregate the information provided by climate model outputs into a manageable set of relevant metrics on which assessments of climate engineering (CE) can be based. From all the variables potentially available from climate models, indicators need to be selected that are able to inform scientists and society on the development of the Earth system under CE, as well as on possible impacts and side effects of various ways of deploying CE or not. However, the indicators used so far have been largely identical to those used in climate change assessments and do not visibly reflect the fact that indicators for assessing CE (and thus the metrics composed of these indicators) may be different from those used to assess global warming. Until now, there has been little dedicated effort to identifying specific indicators and metrics for assessing CE. We here propose that such an effort should be facilitated by a more decision‐oriented approach and an iterative procedure in close interaction between academia, decision makers, and stakeholders. Specifically, synergies and trade‐offs between social objectives reflected by individual indicators, as well as decision‐relevant uncertainties should be considered in the development of metrics, so that society can take informed decisions about climate policy measures under the impression of the options available, their likely effects and side effects, and the quality of the underlying knowledge base.

To enable fair, comprehensive and comparative decision-making on Climate Engineering, we need to foster a multidisciplinary and integrative selection process for assessment metrics. In this session we want to learn to what extent established climate-change assessment metrics are applicable for Climate Engineering assessment and what kind of extensions are needed. This session aims to foster discussions about approaches to comparatively assess different climate engineering (CE) ideas, both among each other and in the context of mitigation. We encourage contributions that address the following questions: How can effects of SRM and CDR methods be compared with each other and with classical mitigation approaches? Which indicators are useful for a comprehensive assessment of SRM and CDR methods? To what extent are structurally new metrics compared to global warming mitigation assessment metrics needed for CE? How can uncertainty be treated explicitly in metrics design? What new challenges arise for the assessment process when different CE methods are combined? How to select indicators for a fair and comprehensive comparison of different CE methods? How to ensure societal relevance of the assessment criteria? How should stakeholders co-shape the design of metrics? Climate engineering (CE) alters prevailing correlations between Earth system variables, hence an appropriate assessment of CE must include a reevaluation of the chosen assessment indicators. A fair comparison of CE methods presents an additional challenge, since they aim at manipulating different components of the Earth system. This study systematically identifies changes in correlation patterns introduced by three idealized Climate Engineering (CE) scenarios: Large-scale Afforestation (LAF), Ocean Alkalinity Enhancement (OAE) and Solar Radiation Management (SRM). Firstly, we investigate changes in prevailing correlations between Earths system variables of the single CE scenarios compared to two future emission scenarios, and the implications of such changes on chosen assessment indicators. Secondly, we evaluate a common correlation matrix and identify a set of 14 indicators for a comprehensive comparison of the three CE scenarios. The evaluation of the CE scenarios relative to a defined reference climate state shows, that each CE method can be found to show a good performance, depending on the given indicator. It is beyond the scope of this study to give a value judgement on which of these variables is of higher importance for society, but here we aim to provide the natural science knowledge to enable such a discussion.

Climate Engineering (CE) as an option to prevent dangerous climate change has reached the political debate. For a well informed decision on CE research and deployment in the future, work towards a comprehensive, comparative assessment is needed. In the first part of this thesis, climate impacts and side effects of an artificial Arctic ocean albedo modification scheme are studied. The second part of this thesis presents a parameter sensitivity study on the uncertainty in the response of transpiration to CO2 and implications for climate change. Is the application of indicators used for the historical time period valid for a comprehensive assessment of future climate change? In the third part of the thesis we introduce a methodological approach to systematically evaluate correlation matrices, identifying robust indicators from Earth system variables, to be used in a natural-science based assessment. In the fourth part of this thesis this method is applied to three exemplary CE scenarios: Large-scale afforestation, ocean alkalinity enhancement and solar radiation management. Changes in correlation patterns provide information on which variables might become more relevant under CE scenarios. To enable a comprehensive comparison of the three scenarios, the common correlation matrix is systematically evaluated to identify an indicator set. A preliminary evaluation of the three scenarios based on these indicators remains inconclusive. If the indicators are further aggregated into a metric to reduce the complexity, a ranking of the different scenarios becomes evident. Given all assumptions, we find that overall the RCP4.5 scenario performs ’best’ in staying close to todays climate state. Solar Radiation Management is identified as the ’best’ CE scenario, followed by Ocean Alkalinity Enhancement and Large-scale Afforestation. These analyses advance the natural-science based assessment of CE, which is essential prior to a decision making process. Auf politischer Ebene hat man begonnen über Climate Engineering (CE) als mögliche Option gegen den mensch-gemachten Klimawandel zu sprechen. Um gut informierte Entscheidungen zum Thema zukünftiger Forschung oder potentiellen Umsetzung von CE Massnahmen zu treffen, benötigt man eine umfassende und vergleichende Einschätzung der verschiedenen Methoden. Im ersten Teil der Arbeit werden Effekte und Nebenwirkungen der CE Methode Ozeanoberlächenaufhellung in der Arktis (AOAM) untersucht. Im zweiten Teil der Arbeit wird eine Parameter Studie zur CO2 Sensitivität von Vegetationstranspiration vorgestellt. Ist es ausreichend die Indikatoren für die historische Zeitspanne zu benutzen, um zukünftigen Klimawandel umfassend zu beschreiben? Im dritten Teil der Arbeit wird eine Methodik eingeführt, um systematisch Korrelationsmatrizen auszuwerten. Das ermöglicht die Identifizierung eines Indikatorensets für eine umfassende, naturwissenschaftliche Beurteilung der gegebenen Fragestellung. Im vierten Teil der Arbeit wird diese Methode auf drei CE Szenarien angewendet, wodurch Änderungen in den jeweiligen Korrelationsmustern gegenüber der zwei Klimawandel Szenarien identifiziert werden können. Eine erste Beurteilung der drei exemplarischen CE Methoden, basierend auf den ausgewählten Indikatoren, bleibt zunächst ergebnislos. Erst wenn die Indikatoren zu einer Metrik zusammen gefasst werden, gelangen wir zu einem klareren Ranking der Szenarien. Unter den gegebenen Annahmen, stellen wir fest, dass das RCP4.5 Szenario am nächsten an dem gewählten Referenzklimazustand bleibt. Das Strahlungsmanagement Szenario ist das ’beste’ CE Szenario, gefolgt von der Ozeankalkung und der gross-skaligen Aufforstung. Diese Analysen bringen das naturwissenschaftliche Verständnis von verschiedenen CE Methoden voran, welches massgeblich für eine spätere Entscheidungsfindung ist.

The MARIA S. MERIAN expedition MSM21/1a was carried out jointly by the Institut f��r Meereskunde at the KlimaCampus of the University of Hamburg and the Helmholtz Centre for Ocean Research Kiel, GEOMAR. The cruise main objectives were related to investigations on water mass transformation processes and transports in the northern North Atlantic and included: - Recovery of a pilot-mooring array (FP1, FP2) to study the export of deep waters from the Labrador Sea through Flemish Pass - Redeployment of five moorings (K8, K9, K10, DSOW1, DSOW2) at the southern exist of the Labrador Sea (53��N array) and enhancement of the array by one mooring (K7) - Deployment of six bottom pressure sensors (P1 to P6) at two areas in the Labrador Sea shelf edge at three different depth (500, 100, 1500m) - Redeployment of a mooring in the Central Irminger Sea (CIS) - Recovery of four (G1, F2, UK1, UK2) and redeployment of two (UK1, UK2) moorings in the Denmark Strait overflow off Angmagssalik. - Acquisition of synoptic hydrography/currents/oxygen data at key sections in the sub polar North Atlantic. The scientific aspects of this work were supported through the BMBF project North Atlantic and the EU FP7 project THOR. In addition to staff members from the above mentioned institutions, one technician from the U.K. Lowestoft Laboratory of CEFAS, U.K., four master students from the Universities of Kiel and Hamburg, and a bird observer from Environment Canada participated in the cruise and supported the field work., MARIA S. MERIAN-Berichte

The remaining carbon budget represents the total amount of CO2 that can still be emitted in the future while limiting global warming to a given temperature target. Remaining carbon budget estimates range widely, however, and this uncertainty can be used to either trivialize the most ambitious mitigation targets by characterizing them as impossible, or to argue that there is ample time to allow for a gradual transition to a low-carbon economy. Neither of these extremes is consistent with our best understanding of the policy implications of remaining carbon budgets. Understanding the scientific and socio-economic uncertainties affecting the size of the remaining carbon budgets, as well as the methodological choices and assumptions that underlie their calculation, is essential before applying them as a policy tool. Here we provide recommendations on how to calculate remaining carbon budgets in a traceable and transparent way, and discuss their uncertainties and implications for both international and national climate policies., Nature Geoscience, 13 (12), ISSN:1752-0908, ISSN:1752-0894

The amount of additional future temperature change following a complete cessation of CO2 emissions is a measure of the unrealized warming to which we are committed due to CO2 already emitted to the atmosphere. This “zero emissions commitment” (ZEC) is also an important quantity when estimating the remaining carbon budget – a limit on the total amount of CO2 emissions consistent with limiting global mean temperature at a particular level. In the recent IPCC Special Report on Global Warming of 1.5 ∘C, the carbon budget framework used to calculate the remaining carbon budget for 1.5 ∘C included the assumption that the ZEC due to CO2 emissions is negligible and close to zero. Previous research has shown significant uncertainty even in the sign of the ZEC. To close this knowledge gap, we propose the Zero Emissions Commitment Model Intercomparison Project (ZECMIP), which will quantify the amount of unrealized temperature change that occurs after CO2 emissions cease and investigate the geophysical drivers behind this climate response. Quantitative information on ZEC is a key gap in our knowledge, and one that will not be addressed by currently planned CMIP6 simulations, yet it is crucial for verifying whether carbon budgets need to be adjusted to account for any unrealized temperature change resulting from past CO2 emissions. We request only one top-priority simulation from comprehensive general circulation Earth system models (ESMs) and Earth system models of intermediate complexity (EMICs) – a branch from the 1 % CO2 run with CO2 emissions set to zero at the point of 1000 PgC of total CO2 emissions in the simulation – with the possibility for additional simulations, if resources allow. ZECMIP is part of CMIP6, under joint sponsorship by C4MIP and CDRMIP, with associated experiment names to enable data submissions to the Earth System Grid Federation. All data will be published and made freely available.

The remaining carbon budget represents the total amount of CO2 that can still be emitted in the future while limiting global warming to a given temperature target. Remaining carbon budget estimates range widely, however, and this uncertainty can be used to either trivialize the most ambitious mitigation targets by characterizing them as impossible, or to argue that there is ample time to allow for a gradual transition to a low-carbon economy. Neither of these extremes is consistent with our best understanding of the policy implications of remaining carbon budgets. Understanding the scientific and socio-economic uncertainties affecting the size of the remaining carbon budgets, as well as the methodological choices and assumptions that underlie their calculation, is essential before applying them as a policy tool. Here we provide recommendations on how to calculate remaining carbon budgets in a traceable and transparent way, and discuss their uncertainties and implications for both international and national climate policies.

The amount of additional future temperature change following a complete cessation of CO2 emissions is a measure of the unrealized warming to which we are committed due to CO2 already emitted to the atmosphere. This “zero emissions commitment” (ZEC) is also an important quantity when estimating the remaining carbon budget – a limit on the total amount of CO2 emissions consistent with limiting global mean temperature at a particular level. In the recent IPCC Special Report on Global Warming of 1.5 ∘C, the carbon budget framework used to calculate the remaining carbon budget for 1.5 ∘C included the assumption that the ZEC due to CO2 emissions is negligible and close to zero. Previous research has shown significant uncertainty even in the sign of the ZEC. To close this knowledge gap, we propose the Zero Emissions Commitment Model Intercomparison Project (ZECMIP), which will quantify the amount of unrealized temperature change that occurs after CO2 emissions cease and investigate the geophysical drivers behind this climate response. Quantitative information on ZEC is a key gap in our knowledge, and one that will not be addressed by currently planned CMIP6 simulations, yet it is crucial for verifying whether carbon budgets need to be adjusted to account for any unrealized temperature change resulting from past CO2 emissions. We request only one top-priority simulation from comprehensive general circulation Earth system models (ESMs) and Earth system models of intermediate complexity (EMICs) – a branch from the 1 % CO2 run with CO2 emissions set to zero at the point of 1000 PgC of total CO2 emissions in the simulation – with the possibility for additional simulations, if resources allow. ZECMIP is part of CMIP6, under joint sponsorship by C4MIP and CDRMIP, with associated experiment names to enable data submissions to the Earth System Grid Federation. All data will be published and made freely available., Geoscientific Model Development, 12 (10), ISSN:1991-9603, ISSN:1991-959X

The remaining carbon budget quantifies the future CO2 emissions to limit global warming below a desired level. Carbon budgets are subject to uncertainty in the Transient Climate Response to Cumulative CO2 Emissions (TCRE), as well as to non-CO2 climate influences. Here we estimate the TCRE using observational constraints, and integrate the geophysical and socioeconomic uncertainties affecting the distribution of the remaining carbon budget. We estimate a median TCRE of 0.44 °C and 5–95% range of 0.32–0.62 °C per 1000 GtCO2 emitted. Considering only geophysical uncertainties, our median estimate of the 1.5 °C remaining carbon budget is 440 GtCO2 from 2020 onwards, with a range of 230–670 GtCO2, (for a 67–33% chance of not exceeding the target). Additional socioeconomic uncertainty related to human decisions regarding future non-CO2 emissions scenarios can further shift the median 1.5 °C remaining carbon budget by ±170 GtCO2., Communications Earth & Environment, 2 (1), ISSN:2662-4435