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The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year−1, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year−1 in observational product and +0.54 PgCO2-e year−1 in model median) and CH4 (+0.21 PgCO2-e year−1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%–60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate.

Humans are significantly impacting ecosystems worldwide. Scientists of the IPBES Global Assessment are therefore calling for a transformative change that includes all aspects of society in order to address drivers of biodiversity loss. However, these calls are rather abstract, and thus it remains unclear how this goal can be achieved.    With this conceptual contribution, we present an analytical framework for evaluating existing processes of societal change which are enhancing biodiversity, and we illustrate its application using three case studies in Germany. We argue that an empirical analysis provides insights into the causal mechanisms that initiate or promote change processes. In doing so, we can draw recommendations for future transformative change processes with regard to biodiversity conservation. In our analysis, we are dealing with questions concerning the following three areas: the drivers and context of societal change processes, the change processes themselves and finally their impacts.    Subsequently, we generate recommendations on how to enhance and support the process of future societal transformation that aims at biodiversity conservation: (a) Retaining co-benefits for biodiversity with goals that are primarily focussing on other objectives; (b) harmonising biodiversity use and conservation by turning conflicts into drivers of transformation; (c) prioritising biodiversity conservation by taking advantage of windows of opportunity.    With our conceptual framework, we provide an analytical tool to learn from existing processes of societal change how to support future transformative change. This is an important step that contributes to the generation of relevant knowledge of promoting transformative change for nature and people.

The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is similar to 60% larger in models (-0.72 vs. -0.44 PgC year-1, 1998-2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year-1 in observational product and +0.54 PgCO2-e year-1 in model median) and CH4 (+0.21 PgCO2-e year-1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%-60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate. The coastal ocean regulates greenhouse gases. It acts as a sink of carbon dioxide (CO2) but also releases nitrous oxide (N2O) and methane (CH4) into the atmosphere. This synthesis contributes to the second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2) and provides a comprehensive view of the coastal air-sea fluxes of these three greenhouse gases at the global scale. We use a multi-faceted approach combining gap-f

The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year−1, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year−1 in observational product and +0.54 PgCO2-e year−1 in model median) and CH4 (+0.21 PgCO2-e year−1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%–60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate., SCOPUS: ar.j, info:eu-repo/semantics/published

The Southern Ocean is a major sink of atmospheric CO2, but the nature and magnitude of its variability remains uncertain and debated. Estimates based on observations suggest substantial variability that is not reproduced by process-based ocean models, with increasingly divergent estimates over the past decade. We examine potential constraints on the nature and magnitude of climate-driven variability of the Southern Ocean CO2 sink from observation-based air-sea O-2 fluxes. On interannual time scales, the variability in the air-sea fluxes of CO2 and O-2 estimated from observations is consistent across the two species and positively correlated with the variability simulated by ocean models. Our analysis suggests that variations in ocean ventilation related to the Southern Annular Mode are responsible for this interannual variability. On decadal time scales, the existence of significant variability in the air-sea CO2 flux estimated from observations also tends to be supported by observation-based estimates of O-2 flux variability. However, the large decadal variability in air-sea CO2 flux is absent from ocean models. Our analysis suggests that issues in representing the balance between the thermal and non-thermal components of the CO2 sink and/or insufficient variability in mode water formation might contribute to the lack of decadal variability in the current generation of ocean models.This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

The Southern Ocean is a major sink of atmospheric CO 2, but the nature and magnitude of its variability remains uncertain and debated. Estimates based on observations suggest substantial variability that is not reproduced by process-based ocean models, with increasingly divergent estimates over the past decade. We examine potential constraints on the nature and magnitude of climate-driven variability of the Southern Ocean CO 2 sink from observation-based air-sea O 2 fluxes. On interannual time scales, the variability in the air-sea fluxes of CO 2 and O 2 estimated from observations is consistent across the two species and positively correlated with the variability simulated by ocean models. Our analysis suggests that variations in ocean ventilation related to the Southern Annular Mode are responsible for this interannual variability. On decadal time scales, the existence of significant variability in the air-sea CO 2 flux estimated from observations also tends to be supported by observation-based estimates of O 2 flux variability. However, the large decadal variability in air-sea CO 2 flux is absent from ocean models. Our analysis suggests that issues in representing the balance between the thermal and non-thermal components of the CO 2 sink and/or insufficient variability in mode water formation might contribute to the lack of decadal variability in the current generation of ocean models. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

The ocean plays a central role in modulating the Earth’s carbon cycle. Monitoring how the ocean carbon cycle is changing is fundamental to managing climate change. Satellite remote sensing is currently our best tool for viewing the ocean surface globally and systematically, at high spatial and temporal resolutions, and the past few decades have seen an exponential growth in studies utilising satellite data for ocean carbon research. Satellite-based observations must be combined with in-situ observations and models, to obtain a comprehensive view of ocean carbon pools and fluxes. To help prioritise future research in this area, a workshop was organised that assembled leading experts working on the topic, from around the world, including remote-sensing scientists, field scientists and modellers, with the goal to articulate a collective view of the current status of ocean carbon research, identify gaps in knowledge, and formulate a scientific roadmap for the next decade, with an emphasis on evaluating where satellite remote sensing may contribute. A total of 449 scientists and stakeholders participated (with balanced gender representation), from North and South America, Europe, Asia, Africa, and Oceania. Sessions targeted both inorganic and organic pools of carbon in the ocean, in both dissolved and particulate form, as well as major fluxes of carbon between reservoirs (e.g., primary production) and at interfaces (e.g., air-sea and land–ocean). Extreme events, blue carbon and carbon budgeting were also key topics discussed. Emerging priorities identified include: expanding the networks and quality of in-situ observations; improved satellite retrievals; improved uncertainty quantification; improved understanding of vertical distributions; integration with models; improved techniques to bridge spatial and temporal scales of the different data sources; and improved fundamental understanding of the ocean carbon cycle, and of the interactions among pools of carbon and light

Abrupt changes in ocean biogeochemical variables occur as a result of human-induced climate forcing as well as those which are more gradual and occur over longer timescales. These abrupt changes have not yet been identified and quantified to the same extent as the more gradual ones. We review and synthesise abrupt changes in ocean biogeochemistry under human-induced climatic forcing. We specifically address the ocean carbon and oxygen cycles because the related processes of acidification and deoxygenation provide important ecosystem hazards. Since biogeochemical cycles depend also on the physical environment, we also describe the relevant changes in warming, circulation, and sea ice. We include an overview of the reversibility or irreversibility of abrupt marine biogeochemical changes. Important implications of abrupt biogeochemical changes for ecosystems are also discussed. We conclude that there is evidence for increasing occurrence and extent of abrupt changes in ocean biogeochemistry as a consequence of rising greenhouse gas emissions.

Non-technical summary We identify a set of essential recent advances in climate change research with high policy relevance, across natural and social sciences: (1) looming inevitability and implications of overshooting the 1.5°C warming limit, (2) urgent need for a rapid and managed fossil fuel phase-out, (3) challenges for scaling carbon dioxide removal, (4) uncertainties regarding the future contribution of natural carbon sinks, (5) intertwinedness of the crises of biodiversity loss and climate change, (6) compound events, (7) mountain glacier loss, (8) human immobility in the face of climate risks, (9) adaptation justice, and (10) just transitions in food systems. Technical summary The Intergovernmental Panel on Climate Change Assessment Reports provides the scientific foundation for international climate negotiations and constitutes an unmatched resource for researchers. However, the assessment cycles take multiple years. As a contribution to cross- and interdisciplinary understanding of climate change across diverse research communities, we have streamlined an annual process to identify and synthesize significant research advances. We collected input from experts on various fields using an online questionnaire and prioritized a set of 10 key research insights with high policy relevance. This year, we focus on: (1) the looming overshoot of the 1.5°C warming limit, (2) the urgency of fossil fuel phase-out, (3) challenges to scale-up carbon dioxide removal, (4) uncertainties regarding future natural carbon sinks, (5) the need for joint governance of biodiversity loss and climate change, (6) advances in understanding compound events, (7) accelerated mountain glacier loss, (8) human immobility amidst climate risks, (9) adaptation justice, and (10) just transitions in food systems. We present a succinct account of these insights, reflect on their policy implications, and offer an integrated set of policy-relevant messages. This science synthesis and science communica

Fossil fuel combustion, land use change and other human activities have increased the atmospheric carbon dioxide (CO2) abundance by about 50% since the beginning of the industrial age. The atmospheric CO2 growth rates would have been much larger if natural sinks in the land biosphere and ocean had not removed over half of this anthropogenic CO2. As these CO2 emissions grew, uptake by the ocean increased in response to increases in atmospheric CO2 partial pressure (pCO2). On land, gross primary production also increased, but the dynamics of other key aspects of the land carbon cycle varied regionally. Over the past three decades, CO2 uptake by intact tropical humid forests declined, but these changes are offset by increased uptake across mid- and high-latitudes. While there have been substantial improvements in our ability to study the carbon cycle, measurement and modeling gaps still limit our understanding of the processes driving its evolution. Continued ship-based observations combined with expanded deployments of autonomous platforms are needed to quantify ocean-atmosphere fluxes and interior ocean carbon storage on policy-relevant spatial and temporal scales. There is also an urgent need for more comprehensive measurements of stocks, fluxes and atmospheric CO2 in humid tropical forests and across the Arctic and boreal regions, which are experiencing rapid change. Here, we review our understanding of the atmosphere, ocean, and land carbon cycles and their interactions, identify emerging measurement and modeling capabilities and gaps and the need for a sustainable, operational framework to ensure a scientific basis for carbon management.

Comparing the impacts of future scenarios is essential for developing and guiding the political sustainability agenda. This review-based analysis compares six IPBES scenarios for their impacts on 17 Sustainable Development Goals (SDGs) and 20 biodiversity targets (Aichi targets) for the Europe and Central Asia regions. The comparison is based on a review of 143 modeled scenarios synthesized in a plural cost–benefit approach which provides the distances to multiple policy goals. We confirm and substantiate the claim that transformative change is vital but also point out which directions for political transformation are to be preferred. The hopeful message is that large societal losses might still be avoided, and multiple benefits can be generated over the coming decades and centuries. Yet, policies will need to strongly steer away from scenarios based on regional competition, inequality, and economic optimism.

Der Ausbau der Windenergie an Land verursacht räumliche Zielkonflikte, etwa zwischen der Minimierung von Stromsystemkosten, dem Anwohnerund Naturschutz oder der interregionalen Gerechtigkeit. Wo in Deutschland in welchem Umfang zukünftig Windräder installiert werden sollten, um die Energiewendeziele zu erreichen, hängt daher maßgeblich davon ab, wie diese Kriterien gewichtet werden. Die vorliegende Studie verdeutlicht mithilfe eines Planspiels, dass es unter Expertinnen und Experten keine allgemein akzeptierte Rangfolge von Kriterien für die räumliche Verteilung des Windenergieausbaus an Land gibt. Die Ergebnisse des Planspiels zeigen zudem, dass alle Expertinnen und Experten Gerechtigkeit bei der interregionalen Verteilung des Windenergieausbaus als wichtig erachten. Es bestehen jedoch unterschiedliche Vorstellungen darüber, wie genau interregionale Gerechtigkeit zu verstehen ist. Die Studienergebnisse unterstreichen einmal mehr die Wichtigkeit transparenter und partizipativer Verfahren für Standortentscheidungen bei der Windenergie an Land. The deployment of onshore wind energy involves spatial trade-offs, e. g. between the minimisation of energy system costs, the mitigation ofimpacts on humans and biodiversity, and interregional equity concerns. The weighting of these criteria is decisive to determine where wind turbines should be installed in the future to attain Germany's energy transition targets. The results of a simulation game played with experts illustrate that there is no unanimously agreed ranking of criteria to guide the spatial allocation of onshore wind energy. Experts agreed that interregional equity concerns should matter for the spatial allocation of wind turbines. However, they also revealed quite different understandings of what constitutes a spatially equitable interregional allocation. These results underpin once more the importance of transparent and participatory decision-making for onshore wind turbine siting decisions.

The deployment of onshore wind power involves spatial sustainability trade-offs, e.g., between the minimization of energy system costs, the mitigation of impacts on humans and biodiversity, and interregional equity concerns. We analyze challenges arising for decision-making if wind power generation capacity has to be allocated spatially in the presence of such trade-offs. The analysis is based on a participatory multi-criteria analysis that involved stakeholders in Germany. Stakeholders were asked to play a serious game during which they had to allocate wind power generation capacity to German states. The results of the serious game illustrate that there is no unanimously agreed ranking of sustainability criteria among the participating stakeholders. They disagreed not only on the weights of different criteria but also their definition and measurement. Group discussions further revealed that interregional equity concerns mattered when generation capacity was allocated to states. Yet, stakeholders used quite different concepts of interregional equity, including approaches of both distributional and commutative justice. The results support the importance of transparent, multi-level and participatory approaches to take decisions on the spatial allocation of wind power generation capacity.

The deployment of onshore wind power involves spatial sustainability trade-offs, e.g., between the minimization of energy system costs, the mitigation of impacts on humans and biodiversity, and equity concerns. We analyze challenges arising for decision-making if wind power generation capacity has to be allocated spatially in the presence of such trade-offs. The analysis is based on a game developed for and played by stakeholders in Germany. The results of the game illustrate that there is no unanimously agreed ranking of sustainability criteria among the participating stakeholders. They disagreed not only on the weights of different criteria but also their definition and measurement. Group discussions further revealed that equity concerns mattered for spatial allocation. Yet, stakeholders used quite different concepts of equity. The results support the importance of transparent, multi-level and participatory approaches to take decisions on the spatial allocation of wind power generation capacity.

The expansion and intensification of agriculture as well as the associated land clearing are threatening both biodiversity and human wellbeing in tropical areas. Implementing agroforestry systems through a landscape approach has a strong potential for integrating nature conservation objectives into agricultural systems. A key challenge for implementing the landscape approach is that political processes and conservation initiatives operate in ‘silos’, being largely disconnected from farmers and local key agents responsible for tree governance. In this study we brought together different stakeholders in facilitated, structured focus discussions to analyse the role of actor groups in tree governance. We used social network analysis to quantitatively and qualitatively analyse agroforestry governance networks and actor interactions related to information exchange, finance flows, and regulation. The analyses were conducted at national, sub-national and local levels in four countries: Honduras, Peru, Indonesia, and Uganda. Using trees on farms as a boundary object enabled all participants to bridge common interests and illuminate some of the constraints and opportunities of local governance systems while overcoming institutional and ideological barriers. The quantitative results of the social network analysis identify a strong density of actor linkages. Despite this density, results indicate incoherent and fragmented actor networks undermining the support for agroforestry on all levels. Nevertheless, existing processes related to finance, information, and regulation can be better aligned to ensure an effective implementation and mainstreaming of agroforestry for biodiversity conservation. Building social capital among key actors on both national and local levels can reveal a strong potential for adaptive learning processes mainstreaming agroforestry as essential component of “good farming” and integrating incentive systems for a coherent and effective agroforestry governan