Description: The Arctic is the region on Earth expected to experience the highest rate of warming caused by climate change. Ocean warming is directly and indirectly decreasing oxygen concentration in the ocean, therewith confronting marine biota with a change of two crucial abiotic factors. Polar cod Boreogadus saida is an Arctic key stone species due to its central position in the food web. In order to contribute to a better understanding of its upper thermal limits and the synergistic effects of warming and decreasing oxygen availability on its metabolic and swimming capacity, Polar cod were acclimated to a temperature hypothesised to belong to its upper thermal limit (10°C) over 10 months. Using static and swim tunnel respirometry 10°C were found to clearly belong to the pejus temperature range of Polar cod although aerobic scope and swimming capacity were maintained at this temperature. No metabolic compensation was observed for standard metabolic rate that increased by a factor of five. A significant PO2 effect on maximum metabolic rate and aerobic scope was observed when measuring metabolic and swimming capacity at decreasing ambient oxygen levels. Polar cod displayed oxy regulation over the whole PO2 range tolerated. Critical velocity stayed stable until 40% ambient O2 saturation whereas gait transition velocity decreased non-significantly at 50% O2. Temperature had a strong negative effect on hypoxia tolerance by increasing Pcmax and Pcrit to 12.53 and 5.22 kPa O2, respectively. We observed that water masses of 10°C can be tolerated in short-term by Polar cod but do not allow for population survival. Hypoxia tolerance was found to be strongly decreased at the long-term incubation temperature but still remained high in inter-species comparison and with respect to 10°C as pejus temperature. Future research should address hypoxia tolerance of Polar cod during acute warming to understand the physiological impacts during marine heatwaves.

Description: The aim of this study is to contribute to a learning process about innovative and successful approaches to overcoming problems and challenges of urban environmental protection. To this end, a detailed overview of the importance of environmental challenges, political priorities and successful solutions in selected countries and cities is given. Based on this, the study analyzes specific success factors and discusses the extent to which these can be transferred and replicated to other cities. Finally, recommendations are made for cities, countries and the international community on how environmental protection at the urban level can be further strengthened. The role of German cities and institutions will also be discussed. The case studies analyzed include Belo Horizonte in Brazil, Moscow in Russia, Kochi in India, Beijing in China, Cape Town in South Africa and Jakarta in Indonesia. These cities were selected because they have already implemented successful policies, measures and other initiatives in the past. For each city, the study analyzes relevant policy documents in order to present the respective challenges and political priorities. The analysis aims to understand the effectiveness of the plans and instruments taking into account the national political environment. Despite the cross-sectoral approach, the analysis of each case study focuses on specific sectors in order to produce well-founded results. The success factors that are worked out based on this sectoral analysis are placed in a holistic context in order to be able to make generalizable statements about success factors.

Description: The objective of this report is to use historical analysis to identify conditions that determine when offsets add value to compliance schemes while upholding environmental integrity. The indicators of success include: increased acceptance of introducing compliance schemes; raising ambition in subsequent compliance periods; the possibility to drive emission reductions outside the compliance sectors; promoting investments in sustainable development; and avoiding perverse incentives that undermine the stringency of the compliance scheme or compliance actors’ efforts in reducing their own emissions. Through undertaking in-depth case study analyzes on the effects of offsets in the European Union, Alberta, Australia, Colombia and Japan, the report identifies common conditions that explain why offsets were successful (or not) in achieving individual indicators. The report further identifies two common conditions that can help explain when offsets achieve all five indicators of success. The first is that policymakers need to be willing to design the compliance scheme to set and maintain a strong compliance price signal that justifies the need for incorporating cost containment measures, such as offsets, to avert negative political and economic ramifications. Relatedly, the second condition requires institutions, processes and infrastructure that govern both the compliance scheme and offsets to be well developed so that they can ensure offsets uphold the principles of environmental integrity, achieve sustainable development benefits, and act as a reliable cost containment measure to high compliance prices. The findings also highlight how difficult it is to achieve both conditions, as both domestic and international political economy factors determine whether policymakers and voters are willing to introduce and maintain compliance schemes that deliver effective action on climate.

Description: The Paris Agreement combines collective goals with individual countries' contributions. This hybrid approach does not guarantee that the individual contributions add up to what is required to meet the collective goals. The Paris Agreement therefore established the Global Stocktake. Its task is to "assess collective progress" towards achieving the long-term goals of the agreement as of 2023 and every five years thereafter. Corresponding to this role, this report addresses three questions: What should an effective Global Stocktake look like? What information and data are needed? Is it possible to execute an effective Global Stocktake within the mandate of the Paris Agreement?

Description: Effective policies to mitigate climate change need to be accompanied by a socially just transition. Based on experiences of past and ongoing transition policies in coal regions in Europe and with indications to the specificity of framework conditions and challenges and to the potential effectiveness and transferability of approaches, this paper presents lessons learnt which can be inspirational for similar transitions in other coal regions and for transitions in other sectors.

Description: Offsetting enables countries and companies to meet part of their climate change mitigation obligations by using mitigation outcomes generated elsewhere - in lieu of own emission reductions. This report explores the future role of offset approaches and how they could be successfully integrated into a post-2020 climate regime by focusing both the supply and demand side. For this purpose, the report develops a conceptual approach that derives a normative vision of what should be considered a successful offset use in a top-down manner to then link this vision to specific factors on the ground in sectors and jurisdictions where offsets will be generated and used. It explores how these factors influence the successful operationalisation of the offset approach and how they can inform its design. In addition, the report also explores six conceptual design aspects to providing recommendations on how to take these factors into account during the design of the offset approach. Based on these findings, the authors derive overarching policy recommendations on the integration of offsets into carbon pricing schemes.

Description: The climate in the summer months is essential for ecosystems and society. However, climate change is causing lasting changes in the characteristics of the summer climate. In order to better understand the summer climate, to capture changes in a statistically meaningful way and to develop climate sce- narios for the future, long-term climate observations and reliable climate models are needed. These three points are addressed in this thesis with the help of three main research questions. The first question examines the prevailing large-scale climate patterns which are elaborated using the climate signature of the oxygen isotope ratio in tree ring cellulose (δ18Ocel) over the past 400 years. An empirical orthogonal function analysis reveals two different modes of variability. The first mode is related to multi-seasonal anomaly patterns associated with the El Niño-Southern Oscillation. The second mode of δ18Ocel variability, which captures a north-south dipole, is associated with a regional summer atmospheric circulation pattern that has a distinct centre over the North Sea. To further exploit the climate sensitivity of δ18Ocel tree-ring records, the first grid-based reconstruc- tion of the European summer vapour pressure deficit (VPD) for the last four centuries is presented. This reconstruction is used to answer the second question of what trends in VPD have occurred in Europe over the last 400 years. The simultaneous increase in temperature and decrease in precipita- tion starts from mid-17th century in Central Europe and the Mediterranean region and relates to a positive VPD trend. This trend towards higher VPD continues throughout the observation period. In addition to studying the past summer climate with the help of a tree ring network, climate models provide valuable information on future scenarios which are highly relevant for society and ecosys- tems. Therefore, this thesis addresses the question of whether simulations with different climate models from a climate model comparison project are suitable for making reliable statements about future drought conditions and what influence the amount of greenhouse gases has on drought oc- currence. Based on a comparison between simulated and observed drought conditions for the period 1971-2000, reasonable agreement can be found between climate model simulations and the observa- tions. However, climate models cannot reproduce drought trends in observations for recent decades for large parts of the Northern Hemisphere. Furthermore, it is shown that drought occurrence is projected to increase significantly in arid regions under three different future scenarios, with the se- verity of droughts depending on greenhouse gas emissions. For regions currently less affected by prolonged droughts, such as the European continent, the climate models show that the probability of drought occurrence increases significantly under the warmest future scenario. Thus, this thesis presents new perspectives on past, present and future European summer climate using a δ18Ocel tree ring network, climate observations and climate model simulations.