Dr. Gian-Kasper Plattner

Achieving net-zero global emissions of carbon dioxide (CO₂), with declining emissions of other greenhouse gases, is widely expected to halt global warming. CO₂ emissions will continue to drive warming until fully balanced by active anthropogenic CO₂ removals. For practical reasons, however, many greenhouse gas accounting systems allow some ‘passive’ CO₂ uptake, such as enhanced vegetation growth owing to CO₂ fertilization, to be included as removals in the definition of net anthropogenic emissions. By including passive CO₂ uptake, nominal net-zero emissions would not halt global warming, undermining the Paris Agreement. Here we discuss measures to address this problem, to ensure residual fossil fuel use does not cause further global warming: land management categories should be disaggregated in emissions reporting and targets to better separate the role of passive CO₂ uptake; where possible, claimed removals should be additional to passive uptake; and targets should acknowledge the need for Geological Net Zero, meaning one tonne of CO₂ permanently restored to the solid Earth for every tonne still generated from fossil sources. We also argue that scientific understanding of Net Zero provides a basis for allocating responsibility for the protection of passive carbon sinks during and after the transition to Geological Net Zero.

In every Intergovernmental Panel on Climate Change (IPCC) Assessment cycle, a multitude of scenarios are assessed, with different scope and emphasis throughout the various Working Group reports and special reports, as well as their respective chapters. Within the reports, the ambition is to integrate knowledge on possible climate futures across the Working Groups and scientific research domains based on a small set of "framing pathways" such as the so-called representative concentration pathways (RCPs) in the Fifth IPCC Assessment Report (AR5) and the shared socioeconomic pathway (SSP) scenarios in the Sixth Assessment Report (AR6). This perspective, initiated by discussions at the IPCC Bangkok workshop in April 2023 on the "Use of Scenarios in AR6 and Subsequent Assessments", is intended to serve as one of the community contributions to highlight the needs for the next generation of framing pathways that is being advanced under the Coupled Model Intercomparison Project (CMIP) umbrella, which will influence or even predicate the IPCC AR7 consideration of framing pathways. Here we suggest several policy research objectives that such a set of framing pathways should ideally fulfil, including mitigation needs for meeting the Paris Agreement objectives, the risks associated with carbon removal strategies, the consequences of delay in enacting that mitigation, guidance for adaptation needs, loss and damage, and for achieving mitigation in the wider context of societal development goals. Based on this context, we suggest that the next generation of climate scenarios for Earth system models should evolve towards representative emission pathways (REPs) and suggest key categories for such pathways. These framing pathways should address the most critical mitigation policy and adaptation plans that need to be implemented over the next 10 years. In our view, the most important categories are those relevant in the context of the Paris Agreement long-term goal, specifically an immediate action (low overshoot) 1.5 °C pathway and a delayed action (high overshoot) 1.5 °C pathway. Two other key categories are a pathway category approximately in line with current (as expressed by 2023) near- and long-term policy objectives, as well as a higher-emission category that is approximately in line with "current policies" (as expressed by 2023). We also argue for the scientific and policy relevance in exploring two "worlds that could have been". One of these categories has high-emission trajectories well above what is implied by current policies and the other has very-low-emission trajectories which assume that global mitigation action in line with limiting warming to 1.5 °C without overshoot had begun in 2015. Finally, we note that the timely provision of new scientific information on pathways is critical to inform the development and implementation of climate policy. Under the Paris Agreement, for the second global stocktake, which will occur in 2028, and to inform subsequent development of nationally determined contributions (NDCs) up to 2040, scientific inputs are required by 2027. These needs should be carefully considered in the development timeline of community modelling activities, including those under CMIP7.

External review is a fundamental component of Global Environmental Assessments, ensuring their processes are comprehensive, objective, open and transparent, and are perceived as such. Here, we focus on review of Intergovernmental Panel on Climate Change (IPCC) Assessment Reports. The review process has received little scrutiny, although review comments and author responses are public. Here we analyse review documents from the Fourth and Fifth Assessments, focusing primarily on Working Group II. We address three questions: Is the review representative? Is it comprehensive? Is it insightful? Overall we found the review process to be fit for purpose, although there are outstanding issues. First, the overwhelming majority of reviewers are from developed countries, although evidence suggests participation by developing country reviewers increased between the Fourth and Fifth Assessments. Second, earlier sections of chapters are more densely reviewed than later ones. This is true even when executive summaries are removed from analysis. In consequence, some sections on specialised topics may escape in-depth review. Thirdly, those review comments which are received make a valid and valuable contribution to the scientific development of chapters. We suggest how outstanding issues could be addressed, including through enhanced reviewer recognition, a wider role for review editors, adherence to mandated page lengths from early in the process, reviewer training, and consistency in reporting to allow systematic evaluation. Making such changes will result in more transparent, consistent and representative processes delivering reviews which effectively contribute to the credibility and legitimacy of future Global Environmental Assessments and, ultimately, their recognition and contribution.

The Swiss Federal Institute WSL strives to increasethe fraction of environmental data that is easily available for reuse. With the Environmental Data portal EnviDat, WSL facilitates the publication of FAIR (Findable, Accessible, Interoperable, Reusable) and high-quality environmental research datasets by providing: A) a formal data publication process for the data producers, B) a technical workflow for improving data-quality with automatic validation, interactive quality checks, and iterative improvement of (meta-)data quality in support of the formal publication process and C) a DataCRediT mechanism for declaration of data authorship roles.

Working Group I (WGI) of the Intergovernmental Panel on Climate Change (IPCC) assesses the current evidence on the physical science of climate change, evaluating knowledge gained from observations, reanalyses, paleoclimate archives and climate model simulations, as well as physical, chemical and biological climate processes. This chapter sets the scene for the WGI assessment, placing it in the context of ongoing global and regional changes, international policy responses, the history of climate science and the evolution from previous IPCC assessments, including the Special Reports prepared as part of this Assessment Cycle. Key concepts and methods, relevant recent developments, and the modelling and scenario framework used in this assessment are presented.

The Environmental Data Portal EnviDat aims to fuse data publication repository functionalities with next-generation web-based environmental geospatial information systems (web-EGIS) and Earth Observation (EO) data cube functionalities. User requirements related to mapping and visualization represent a major challenge for current environmental data portals. The new Cloud Optimized Raster Encoding (CORE) format enables an efficient storage and management of gridded data by applying video encoding algorithms. Inspired by the cloud optimized GeoTIFF (COG) format, the design of CORE is based on the same principles that enable efficient workflows on the cloud, addressing web-EGIS visualization challenges for large environmental time series in geosciences. CORE is a web-native streamable format that can compactly contain raster imagery as a data hypercube. It enables simultaneous exchange, preservation, and fast visualization of time series raster data in environmental repositories. The CORE format specifications are open source and can be used by other platforms to manage and visualize large environmental time series.

Der Klimawandel findet statt - er ist weltweit, in der Schweiz und auch in Riehen eindeutig mess- und spürbar. Die Klimaerwärmung und die vielen daraus resultierenden Effekte werden sich in Zukunft weiter verstärken. Die Auswirkungen auf Natur, Gesellschaft und Wirtschaft sind vielfältig und betreffen alle Regionen der Schweiz und alle Sektoren. Wir werden uns als Gesellschaft an das sich verändernde Klima gewöhnen und anpassen müssen, um negative Auswirkungen möglichst gering zu halten. Zur Eingrenzung des Klimawandels und dessen Folgen ist eine Reduktion der Treibhausgasemissionen unumgänglich.