Archive: Videos and Abstracts

07.11.2024 | Sibel Eker, Radboud University

Improving the representation of social systems in climate policy models

Feasible climate change mitigation pathways require considering the feedbacks within and between human and earth systems. Currently, the models that support climate polices, namely the integrated assessment models (IAMs) of climate, economy and environment have a very weak representation of the human systems and the feedbacks between human and earth systems. In this talk, I will introduce the FeliX model, a feedback-rich system dynamics model of climate, economy, environment and society interactions. I will focus on how the FeliX model is used to explore long-term dietary changes, sustainable development, poverty and human wellbeing resulting from the feedbacks between society, climate, economy, energy and land use dynamics. Based on these examples, I will discuss how system dynamics models can help developing feasible demand-side mitigation scenarios and analyzing the potential of social tipping points.

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11. Juli 2024 | Stefanie Arndt, Universität Hamburg und Alfred Wegener Institut

It’s all about snow: What can we learn from local snow properties for large-scale Antarctic ice pack volume?

Snow on sea ice is a crucial climate variable, affecting energy and momentum exchanges across the atmosphere-ice-ocean interfaces and contributing to the sea ice mass budget. The year-round snow cover on Antarctic sea ice prevents summer surface melt and promotes ice growth through snow-to-ice conversion. However, limited knowledge of seasonal stratigraphy and large-scale snow depth causes significant uncertainties in satellite data and climate models.

The Young Investigator Group SNOWflAke, a joint research group between the University of Hamburg and the Alfred Wegener Institute for Polar and Marine Research (AWI), aims to test the hypothesis that seasonal variations in Antarctic snowpack properties are indicators of atmospheric changes and could trigger snow-albedo feedbacks, accelerating sea ice melt and retreat. This research will develop techniques to create comprehensive snow and sea ice datasets, improve snow parameterization for satellite data, and enhance snow models to reduce uncertainties in sea ice predictions. These efforts will provide insights into Antarctic sea ice changes and snow's role as a climate change indicator.

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04. Juli 2024 | Stephen Sitch, University of Exeter

The role of the terrestrial biosphere in the Earth System and for achieving Paris climate targets

In this presentation I will first give a broad overview of the role of the terrestrial ecosystems in the contemporary global carbon cycle, and ecosystems mitigate climate change already today. A key question relates to the efficiency of land ecosystems to sequester CO2 and how it will change in the near-term future, e.g. can it help us achieve the Paris agreement to avoid dangerous climate change. To begin to answer this question we first need to understand processes and regional attribution of the contemporary land carbon sink, e.g. the relative contribution of changing atmospheric composition, climate and land-use change to the land sink dynamics. I will draw upon research conducted using the TRENDY ensemble of land models which supports the annual Global Carbon Budget. I will highlight recent work in boreal and tropical forests and dryland ecosystems, and the role of cascading effects of deforestation on the land sink. Finally, I present work on how land-use emissions play a critical role in land-based mitigation for Paris climate targets.

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30. Mai 2024 | Christopher Kadow, DKRZ

The technology deleting photobombs can do climate research? The chat bot writing poems can do climate analysis?

Climate change research today relies on climate information from the past. Historical climate records of temperature observations form global gridded datasets that are examined, for example, in IPCC reports. However, the datasets combining measurement records are sparse in the past. Even today, they contain missing values. We found that recently successful image inpainting technologies, such as those found on smartphones to get rid of unwanted objects or people in photos, are useful here. The derived AI networks are able to reconstruct artificially cropped versions in the grid space for any given month using the missing values observation mask. So herewith we have found with AI a technique that gives us data from the past that we never measured with instruments.  Other important datasets used in the Assessment Report 6 of the IPCC to study climate change, as well as advanced applications such as downscaling in atmosphere and ocean, a hybrid (AI&ESM) data assimilation approach within ICON, or precipitation in broken radar fields are shown in this presentation.

Climate research, including the study mentioned in the previous paragraph, often requires substantial technical expertise. This involves managing data standards, various file formats, software engineering, and high-performance computing. Translating scientific questions into code that can answer them demands significant effort. The question is, why? Data analysis platforms like Freva (Kadow et al. 2021, e.g., gems.dkrz.de) aim to enhance user convenience, yet programming expertise is still required. In this context, we introduce a large language model setup and chat bot interface based on GPT-4/ChatGPT, which enables climate analysis without technical obstacles, including language barriers. This approach is tailored to the needs of the broader climate community, which deals with massive data sets from kilometer-scale modeling and requires a processing environment utilizing modern technologies, but addressing society after all - such as those in the Earth Virtualization Engines (EVE eve4climate.org).

Kadow, C., Hall, D.M. & Ulbrich, U. Artificial intelligence reconstructs missing climate information. Nat. Geosci. 13, 408-413 (2020). https://doi.org/10.1038/s41561-020-0582-5

Kadow, C., Illing, S., Lucio-Eceiza, E. E., Bergemann, M., Ramadoss, M., Sommer, P. S., Kunst, O., Schartner, T., Pankatz, K., Grieger, J., Schuster, M., Richling, A., Thiemann, H., Kirchner, I., Rust, H. W., Ludwig, T., Cubasch, U., and Ulbrich, U.: Introduction to Freva – A Free Evaluation System Framework for Earth System Modeling, Journal of Open Research Software, 9, p. 13, https://doi.org/10.5334/jors.253, 2021

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23. Mai 2024 | Louis Kotzé, THE NEW INSTITUTE

Thinking Through Planetary Commons Governance

The Anthropocene signifies the start of a no-analogue trajectory of the Earth system that is fundamentally different from the Holocene. This new trajectory is characterized by rising risks of triggering irreversible and unmanageable shifts in Earth system functioning. We urgently need a new global approach to safeguard critical Earth system regulating functions more effectively and comprehensively. The global commons framework is the closest example of an existing approach with the aim of governing biophysical systems on Earth upon which the world collectively depends. Derived during stable Holocene conditions, the global commons framework must now evolve in the light of new Anthropocene dynamics. This requires a fundamental shift from a focus only on governing shared resources beyond national jurisdiction, to one that secures critical functions of the Earth system irrespective of national boundaries. We propose a new framework—the planetary commons—which differs from the global commons framework by including not only globally shared geographic regions but also critical biophysical systems that regulate the resilience and state, and therefore livability, on Earth. The new planetary commons should articulate and create comprehensive stewardship obligations through Earth system governance aimed at restoring and strengthening planetary resilience and justice.

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11. April 2024 | Da Yang, University of Chicago

The Incredible Lightness of Water Vapor

Conventional wisdom suggests that warm air rises while cold air sinks. However, recent satellite observations show that, on average, rising air is colder than sinking air in the tropical free troposphere. This is due to the buoyancy effect of water vapor: the molar mass of water vapor is less than that of dry air, making humid air lighter than dry air at the same temperature and pressure. Unfortunately, this vapor buoyancy effect has been considered negligibly small and thereby overlooked in large-scale climate dynamics. Here we use theory, reanalysis data, and a hierarchy of climate models to show that vapor buoyancy has a similar magnitude to thermal buoyancy in the tropical free troposphere. As a result, cold air rises in the tropical free troposphere. We further show that vapor buoyancy enhances thermal radiation, increases subtropical stratiform low clouds, favors convective aggregation, and stabilizes Earth’s climate. However, some state-of-the-art climate models fail to represent vapor buoyancy properly. This flaw leads to inaccurate simulations of cloud distributions—the largest uncertainty in predicting climate change. Implications of our results on paleoclimate and planetary habitability will also be discussed.

19. January 2023 | Leonie Wenz, Potsdam Institute for Climate Impact Research

The economic cost of climate change

Changing climate conditions and weather extremes can affect various fundamental elements of our economies such as labor productivity or agricultural yields – thereby posing a threat to economic prosperity and societal welfare. Estimates of the macroeconomic costs of climate change hence play an important role in climate policy debates and decisions. However, current estimates differ strongly – partly because it is unclear how resilient regions, sectors and communities are and how persistently weather extremes can thus affect them. In this talk, I will give an overview of some recent findings in this research area. Specifically, I will present insights gained from a novel data set comprising subnational income data from the past 40 years and more than 1500 regions worldwide. Based on these granular data, we have empirically estimated historic temperature and precipitation impacts at different time scales, from daily fluctuations and extremes to changes in the long-term mean. Our findings show that economic productivity is strongly affected by rainfall and temperature changes but that these effects display large spatial heterogeneity. Whereas low-income, low-latitude regions are most vulnerable to rising and erratic temperatures, increases in the number of rainy days and extreme rainfall events are most harmful in wealthy, industrialized countries. In our economically interconnected world, these local impacts can have repercussions in other parts of the work as well. I will conclude by presenting preliminary results on such spill-over effects in firm networks.

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12. January 2023 | Laure Zanna, Professor of Mathematics & Atmosphere/Ocean Science [she/her] Courant Institute, NYU

Transforming Climate Modeling for Machine Learning: Hype or Reality?

Climate simulations remain one of the best tools to understand and predict global and regional climate change. Uncertainties in climate predictions originate partly from the poor or lacking representation of processes, such as ocean turbulence and clouds, that are not resolved in global climate models but impact the large-scale temperature, rainfall, sea level, etc. The representation of these unresolved processes has been a bottleneck in improving climate simulations and projections. The explosion of climate data and the power of machine learning (ML) algorithms are suddenly offering new opportunities: can we deepen our understanding of these unresolved processes and simultaneously improve their representation in climate models to reduce climate projections uncertainty? In this talk, I will discuss the advantages and challenges of using machine learning for climate projections. I will focus on our recent work in which we leverage ML tools to learn representations of unresolved ocean processes - in particular, learning symbolic expression. Some of our work suggests that machine learning could open the door to discovering new physics from data and enhance existing climate modeling. Yet, many questions remain unanswered, making the next decade exciting and challenging for ML + climate modeling for robust and actionable climate projections. The work presented is part of M²LInES – an international effort to improve climate models with scientific machine learning. 

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15. Dezember 2022 | Michael Byrne, Reader in Earth & Environmental Sciences – University of St Andrews Marie Skłodowska-Curie Research Fellow – University of Oxford

Extreme tropical temperatures in a changing climate: theory and simulations

Understanding the future of extreme temperatures is a critical goal for science and society. Simulations with coupled climate models suggest that hot days over tropical land will warm substantially more than the average day. For example, averaged across models, warming of the hottest 5% of days is projected to be approximately 20% larger than the annual-mean warming. Amplified warming of extreme temperatures implies severe impacts on humans and ecosystems, yet the physical mechanisms underpinning this emergent behaviour of numerical models remain unclear. Here, I interpret the response of extreme temperatures over tropical land to climate change using a theory based on convective coupling and the weak temperature gradient approximation. According to the theory, warming is amplified for hot land days because those days are dry: this is termed the ‘drier get hotter’ mechanism and can be predicted given properties of the current climate. Changes in near-surface relative humidity further increase tropical land warming, with decreases in land relative humidity particularly important. The theory advances understanding of extreme weather in the tropics, and highlights land-surface dryness as a key factor determining how hot days will respond to climate change.

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08. Dezember 2022 | Timo Goeschl, Heidelberg University, Department of Economics and Research Centre for Environmental Economics

Attribution to anthropogenic causes helps prevent adverse events

The science of extreme event attribution (EEA) has rapidly established itself as a popular tool for quantifying - ex post - the anthropogenic contribution to recent adverse events in the climate system. Yet, whether backward-looking causal attribution can lead to future behavioral change is conceptually unclear, and evidence that it can reduce anthropogenic stress on these systems is lacking. Our online experiment with 3,031 participants in three treatment conditions provides a proof of principle. There, adverse events can arise either as a result of excess stress on the system by participants’ pursuit of individual material benefits (anthropogenic cause) or as a result of chance (natural cause). We examine both the impact on future anthropogenic stress of making past adverse events causally attributable and the demand for attributability. We find that whether an adverse event can be causally attributed is behaviorally relevant: Attribution to an anthropogenic cause reduces future anthropogenic stress and leads to fewer adverse events compared to no attributability and compared to attribution to a natural cause. Joint causation has no effect. There is demand for ex-post event attribution in the population of participants, even when costly. The conjecture that attribution science can be behaviorally impactful, socially valuable, and in demand therefore rests on promising experimental foundations.

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03. November 2022 | Steven Yearley, University of Edinburgh, School of Social and Political Science

Has the climate crisis put an end to green ambivalence about science?

The idea at the heart of this colloquium presentation is that there is an elective affinity between environmental campaign organisations/the environmental movement and scientific claims that is, to a large degree, distinctive among social movements. This gives environmentalists and green campaigning bodies an urgent interest in science communication issues and has turned many of them into significant science-communication actors. However, these ties to science have – as is well known – not been problem-free. Demands for scientific “proof” of environmental problems have often been used by governments or regulators as grounds for inaction. Green campaigners have themselves been sceptical about scientific arguments in relation to GMOs and – before that – nuclear safety. At the same time, environmentalists’ opponents have learned to deploy doubt and uncertainty as ways to counter science-based claims. Scientific claims have also typically stemmed from the “Global North”, giving rise to concerns about their applicability or sensitivity to issues in the Global South. Finally, scientific claims are typically presented as empirical assertions and thus non-normative; this may be beneficial when identifying problems but tells one less about solutions and the ways we should live with environmental change. The urgency of the climate crisis intensifies these questions about the environmental movement’s attachment to science: has the climate crisis put an end to green ambivalence about science?

June 24th | Jörg Knieling, HCU Hamburg

Climate Adaptation Governance of "Water from 4 Sides": Of wicked problems and metropolitan complexities in urban systems

"Water from 4 Sides" is one of the projects of CLICCS. In an interdisciplinary team of researchers it looks at climate adaptation in urban systems with regard to different water issues: river flooding, storm surges, heavy rain events, and ground water. For handling these challenges in the societal and political context the governance research provides a broad range of analytical and conceptual approaches including different steering modes and reaching from regulative and informal to economic instruments. However, governance arrangements are challenged by phenomena which complicate 'simple solutions', such as uncertaintiy, multi-level-responsibilities or diverging stakeholder rationalities. The presentation explores how those wicked problems and complexities refer to climate adaptation governance and could be considered in metropolitan strategies.

                                                                                                                                                                               

June 17th | Johanna Baehr, Universität Hamburg

Back to the future: a guided journey through Earth system predictions

Skilful Earth system predictions for a season or a decade ahead remain in many cases a formidable challenge. I will present recent progress in predicting climate and Earth system variability using prediction systems based on the Max-Planck-Institute Earth System Model (MPI-ESM). I will also challenge the current practice to focus on the ensemble mean and suggest a less-is-more approach instead.

                                                                                                                                                                               

June 10th | Grischa Perino, Universität Hamburg

Climate Protest Mobilization is a Strategic Game: Theory, Econometric Application, and Experimental Evidence from the Field

Considering private and collective goods supplied by political mass protest, we model how beliefs regarding the participation of others are critical in protest formation. We test the hypotheses with data from a field experiment that uses an information treatment to identify the effect of beliefs on participation. The study was conducted around the “Third Global Climate Strike” (20.9.19) with adults from the largest four German cities, which was the first attempt to reach out beyond the youth. We find robust evidence that participation decisions are causally related to beliefs about participation of others in a way consistent with “free riding”.

                                                                                                                                                                                

June 3rd | Hartmut Graßl, MPI-M Hamburg

Scientific highlights and major structural changes at MPI for Meteorology since 1975

(as seen by Hartmut Graßl)

Starting in 1975 as a small MPI with one director of (Klaus Hasselmann) and one director at (Hans Hinzpeter), our institute is now among the leading Earth system modelling centres worldwide and also adds new observations for the improvement of models. When I started as a group leader in 6/1976 the scientists and technicians of the institute occupied less than 2 floors in Geomatikum, in close cooperation with the Meteorological Institute of the University of Hamburg. Now we can look back to many early achievements, here mentioning only very few: First coupled atmosphere/ocean/land-model in Europe, first global satellite-based energy flux climatology at the ocean surface, detection of the anthropogenic climate signal. I will also include the stories about the structural changes (foundation of the German Climate Computing Centre in Hamburg) and the threat to close the institute at the turn of the century.

                                                                                                                                                                                

May 27th | Corinna Schrum, HZG Geesthacht

Between Climate Change and fairway deepening: How do models contribute to the development of sustainable future scenarios for the Elbe estuary and the region?

How will climate change impact the Elbe estuary and what are the implications for the city of Hamburg and the port? This is a central question for long-term planning and climate adaptation measures of Hamburg. The Elbe estuary and the harbor is a system, that is influenced by different socio-economic and climate drivers. Climate drivers control the dynamics of the estuary through the water balance in the catchment area and through sea level at the river mouth. Biogeochemical dynamics and sediment transport are moreover controlled by temperature and nutrient loads.  However, climate pressures are not the only drivers of the Elbe estuary, the estuary is also a massively engineered system. Substantial fairway deepening over more than a century but also coastal protection, dikes, punctures and changes of the course of the estuary represent an even stronger control of the Elbe estuarine dynamics.

Today`s management of the estuary takes place in a framework characterized by different federal-state responsibilities. In addition to coastal protection needs and economic objectives it also needs to serve ecological objectives. Conflicting interests and trade-offs often exist and the complex and sometimes unpredicted behavior of the estuarine system complicates management and implementation of climate adaptation measures.      

We here present a model framework that can support the exploration of adaptation options.

The framework couples a global climate model with regional focus and additional sea level rise contributions to a high-resolution estuary model. The framework resolves the most important drivers and feedbacks and meets the level of detail and accuracy requirements needed for planning processes.  

This event was not recorded.

                                                                                                                                                                                

May 20th | Martin Wickel, HCU Hamburg

The German Climate Protection Law after the Decision of the Federal Constitutional Court (german only)

Das Bundesverfassungsgericht hat mit seinem Beschluss zum Klimaschutzgesetz den verfassungsrechtlichen Kerngehalt des Klimaschutzrechts konkretisiert. Stichworte sind die grundrechtlichen Schutzpflichten, das Staatsziel Umweltschutz und vor allem die intertemporale Freiheitssicherung durch die Grundrechte. Damit ändern sich die (verfassungs-)rechtlichen Rahmenbedingungen für den Klimaschutz in Deutschland. Der Vortrag wird beleuchten, welche Erwägungen hinter dem Beschluss stehen, welche Schlussfolgerung das Gericht zieht und wie der Gesetzgeber darauf reagieren muss.

This event took place as a CLICCS Convent instead of the KlimaCampus Colloquium. 

                                                                                                                                                                                

April 22nd | Lars Kutzbach, Universität Hamburg

Methane flux dynamics in permafrost landscapes of the Arctic

Increased methane release from a warming Arctic is expected to be a major feedback on the global climate. However, due to the complex effects of climate change on arctic permafrost landscapes, projections of future land-atmosphere fluxes of methane are highly uncertain. At the same time, empirical data covering the pronounced spatio-temporal variability of methane fluxes is rare due to the logistic and technical difficulties associated with experimental investigations in the Arctic. In this talk, I will present our studies on methane flux variability on spatial and temporal scales conducted in the Siberian Lena River Delta (72.4° N, 126.5° E) between 2002 and 2019.

This event was not recorded.

                                                                                                                                                                                

April 8th | Guy Brasseur, MPI-M

An unintended worldwide experiment: Impact of COVID-19 on the global chemical composition of the atmosphere

The reduction in the emissions of greenhouse gases and air pollutants during COVID-19 offers a glimpse into a potential future in which air quality would be improved. With a global Earth system model, we assess the response of primary and secondary chemical species of the atmosphere to this global atmospheric experiment. We highlight the nonlinear behavior of the chemical system, which makes air pollution mitigation policies difficult to implement. Meteorological variability produces anomalies, sometimes larger than the perturbations attributed to changes in the emissions. This worldwide experiment provides information that should help improve air quality on the different continents.

February 18th | Stefan Aykut, Universität Hamburg

Global climate summits, international cooperation, and the prospects of collective action on the climate crisis

Since the 1990s, global climate summits federate each year delegates from virtually all countries on the planet. They produced a series of treaties, from the 1992 Climate Convention to the 2015 Paris agreement. Increasingly, they also try to facilitate and orchestrate decentralized climate action by firms, investors or municipalities. But what are the results of almost 30 years of global ‘summitry’ in terms of forging an international response to the climate problem? And how do social scientists observe, analyze and assess transnational mega-events that gather tens of thousands of delegates, activists, lobbyists and journalists? In this talk, I present a social science perspective on global climate politics, explain with which methods we study global climate summits, and share some insights from ongoing research.

                                                                                                                                                                               

February 4th | Bjorn Stevens, MPI-M Hamburg

Clouds, Circulation and Climate Sensitivity — EUREC4A!

The response of shallow clouds over the tropical oceans to warming has proven pivotal for assessments of Earth's equilibrium climate sensitivity.  Models that project a strong future warming invariably show a marked reduction in clouds in the trades.  Studies over the past decades have not only helped identify the important role of these clouds for a model's response to radiative forcing (i.e., greenhouse gases), but also the mechanisms underpinning such responses.  By exploiting advances in measurement science, EUREC4A, a Barbadian-German-French led field campaign, collected observations to test these mechanisms.  By demonstrating an ability to measure both clouds, and the circulations in which they were embedded, EUREC4A also made it possible to also address a wide range of additional questions related to the physics that regulate cloud amount in the trades, and to provide benchmark measurements for a new generation of climate models. In this talk, I will present the science behind EUREC4A, its execution, and some snapshots of results emerging less than one year since the campaign's conclusion.

                                                                                                                                                                               

January 28th | Daniela Jacob, GERICS Geesthacht |

Challenges for Climate Services

The need to adapt to climate change has led to the establishment of a new research and service field, called Climate Services, encompassing a variety of activities and formats. It is clear that Climate Services need to be context specific, non-uniform and often cross-sectoral, ‘fit for purpose’ with science-society dialog as a key to develop usable climate services. However, Climate Services still face some challenges. They do not exist in all sectors, exchange with practitioners could be enhanced, sharing experiences world-wide is difficult and clear carrier paths to climate service experts are lacking. The talk will elaborate on these challenges and the needs for climate service in an era of transformation! 

January 30th | Felix Riede, University of Aarhus, Denmark.

Volcanoes, climate and societal change in the prehistory of northern Europe – does the past hold lessons for the future?

Felix Riede is guest of the MPI-M.

Climate change and extreme or compound events are today recognized as major societal challenges yet they play little role in classic ideas of how societies changed in the past. In my presentation, I will present the results of recent research investigating the long-range impacts of volcanic eruptions on climate and, importantly, also on societies in northern Europe. Moving from the still rather close-to-home eruption of the Laacher See volcano in the Eifel to more distant eruptions in the Mediterranean to those located in the far-away reaches of Alaska and Central America, these case studies range from the Late Pleistocene Stone Age to the Bronze and Iron Ages. While covering different sorts of interactions between volcanism, climate and society, we may ask: Does the past hold lessons for the future?

                                                                                                                                                                               

December 19th | Felix Landerer, NASA’s Jet Propulsion Laboratory

Weight-Watching from Space – tracking changes in Earth’s groundwater, glaciers, ice sheets and sea level rise in the last two decades

Felix Landerer is guest of the MPI-M.

Earth's distribution of water - in the form of ice, snow, soil moisture, groundwater, lake and sea level - is undergoing profound changes as the climate changes over seasons to decades. The original Gravity Recovery and Climate Experiment (GRACE) mission, launched in early 2002, has enabled a unique and valuable data record to study changes in our global water cycle, and allowed precise determination of sea-level rise, polar ice-cap mass loss in Greenland and Antarctica, and large-scale water storage changes over land. By measuring small month-to-month changes in Earth's gravity field, these observations provide a unique window into Earth's evolving climate and water stores, and a glimpse into possible future impacts. The twin satellites of the GRACE Follow-On mission, in operation since early 2018, continue and extend this valuable data record. I will describe the fascinating technology behind gravity measurements from space, and present some first new science findings from the new joint US-German GRACE Follow-On mission, such as the variable ice mass loss over Greenland in 2018 and 2019, and the record-low land water storage in Europe during the 2018 drought.

                                                                                                                                                                               

December 12th |  Caroline Ummenhofer, Woods Hole Oceanographic Institution

Extreme climate events with ecological relevance: from droughts and floods on land to marine heat waves along the coast

Caroline Ummenhofer is guest of the MPI-M.

Mounting evidence points towards an increase in intensity and frequency of extreme weather and climate events over recent decades. These changes are being linked to human-induced climate change, while impacts on individual extreme climate events are more difficult to quantify. Limitations in the observational network, both for physical climate system parameters and even more so for long-term ecological monitoring, have hampered progress in understanding the effect of extreme climate events on bio-physical interactions. However, recent advances open new opportunities for developing a mechanistic understanding of how extreme climate events affect human and natural systems. This is illustrated with hydroclimatic extremes, such as droughts and floods, and their effect on terrestrial ecosystems for tropical rainforests, in semi-arid regions, as well as for marine heat waves in the coastal environment.

The hydroclimatic conditions in Australia are used as an example: in 2010/11, severe flooding in northeastern Australia occurred, as well as a rare filling of Lake Eyre and record terrestrial carbon uptake. The severity of the conditions across Australia was unusual, even considering that it was a strong La Niña event. Long-term ocean warming has resulted in 0.5°C warmer sea surface temperatures around the Australian continent over the past 60 years. It is demonstrated that the warmer ocean background state increased the likelihood of the extreme rainfall response and relevant mechanisms are identified. The unusual conditions of the 2010/11 La Niña also had severe implications on the coastal environment around Australia, including prolonged marine heat wave conditions off Western Australia. Using high-resolution ocean model sensitivity experiments, the upper-ocean structure of the marine heat wave is investigated and contributions from wind and buoyancy forcing are quantified.

                                                                                                                                                                               

December 5th | Trude Storelvmo, University of Oslo.

State-dependent cloud feedbacks make equilibrium climate sensitivities > 5°C plausible

Trude Storelvmo is guest of the MPI-M

For decades, global climate models (GCMs) have produced equilibrium climate sensitivities (ECSs) between 2 and 4.5°C, but interestingly that is now about to change: a subset of state-of-the-art GCMs participating in the 6th coupled model intercomparison project is producing ECSs well above 5°C. Here, I present analyses based on one such high-ECS model. In the past, it has been assumed that such very high simulated ECSs would make it practically impossible for GCMs to reproduce the historical temperature record, but that turns out not to be the case. This is because the model in question has a net positive cloud-climate feedback that grows with warming - in other words: the warmer it gets, the more clouds change in a way that further amplifies the warming, while for modest warming the amplification is much smaller. In this presentation I will explain the underlying physical mechanism responsible for the simulated state transition and discuss its general validity and broader implications.

                                                                                                                                                                               

November 14th | Ricarda Winkelmann, Potsdam-Institut für Klimaforschung

Beyond gradual change – Antarctic ice dynamics and tipping points

Ricarda Winkelmann is Guest of the MPI-M.

The Antarctic Ice Sheet is by far the largest potential source of future sea-level change, holding enough water to raise global sea level by 58 m. To this day, the complex dynamics of the ice sheet and its surrounding ice shelves are one of the key challenges for sea-level projections. Recent observations show that part of the West Antarctic Ice Sheet is rapidly retreating, and that this retreat is likely irreversible on human timescales. Other regions are currently protected by ice plugs, hindering the onset of a dynamic instability.

In her talk, Ricarda will discuss the underlying mechanisms and critical thresholds for triggering persistent ice discharge from Antarctic basins. As a consequence, sea-level might continue to rise for centuries or even millennia to come. This long-term perspective illustrates that policy decisions made in the next years to decades will have profound impacts on global climate and sea-level - not just for this century, but for the next millennia and beyond.

                                                                                                                                                                               

November 7th | Elizabeth Barnes, Colorado State University

Viewing Climate Signals through an AI Lens

Elizabeth Barnes is guest of the MPI-M.

Much of climate science is viewed as a signal-to-noise problem and the field has many statistical methods for extracting the signal of interest. Here, we argue that artificial neural networks (ANNs) are an additional useful tool for the “climate toolbox”. As an example, we demonstrate their utility for extracting forced climate patterns from model simulations and observations whereby the ANN identifies patterns that are complex, non-linear combinations of signal and noise. While neural networks are often viewed as black boxes, we further demonstrate how to visualize what the network has learned using recent advances in visualization tools within the computer science community. This approach suggests that viewing climate patterns through an AI lens has the power to uncover new insights into climate variability and change

This event was not recorded.

October 18th | Oliver Fuhrer, Federal Office of Meteorology and Climatology Meteo Swiss

High performance computing for weather and climate: Learning how to forget

Oliver Fuhrer is guest of Bjorn Stevens (MPI-M).

The weather and climate community has set ambitious goals to reach global km-scale modeling capability on future exascale high-performance computing (HPC) systems. Reducing the horizontal resolution to the kilometer-scale holds the promise of reducing some of the long-standing biases and uncertainties. But how far are we from achieving this goal?

The weather and climate community is struggling to keep up with the fast-paced developments as HPC system designs strive towards the Exascale. Only few production-ready community codes are able to leverage emerging hardware architectures. This has become known as the software productivity gap.  While novel programming models - such as OpenACC or CUDA - are available to target these hardware architectures, they further increase the complexity of the code and thus exacerbate the problem.

In this talk, we give an introduction to some of the challenges we are facing. Further, we discuss the experience of a re-design effort for a regional weather and climate model to illustrate a possible alternative pathway. Significant parts of the code have been rewritten based on a domain-specific language (DSL) specifically targeted to the key algorithmic motifs in weather and climate models. The DSL allows a high-level, hardware agnostic formulation of the model which then can be compiled to different hardware targets. Finally, we will demonstrate the capability of the refactored code on the leadership-class heterogeneous HPC system Piz Daint and discuss the implications for global km-scale climate simulations.

                                                                                                                                                                               

November 8th | Philip Stier, Department of Physics, University of Oxford

Observational constraints on clouds, aerosols and their interactions

Philip Stier ist guest of Bjorn Stevens (MPI-M).

Clouds, aerosols and their interactions arguably remain the single greatest uncertainty in our understanding of Earth’s climate response to anthropogenic perturbations. In particular the effects of aerosol-cloud interactions on global and regional radiation budgets and the hydrological cycle remain highly uncertain.

This presentation will critically review some of the achievements made towards quantifying aerosol-cloud interactions, with a particular focus on the role of observations in the evaluation of models across scales.

Starting from the local scale, we will explore model-data synergies in the assessment of the representativeness of observations, an assessment of the suitability of remote-sensing retrievals as well as novel Lagrangian constraints from geostationary satellites.

                                                                                                                                                                               

November 15th | Erich Fischer, Institute for Atmospheric and Climate Science, ETH Zurich

A plethora of noise: Quantifying changes in extremes in the presence of large internal variability

Erich Fischer is guest of Nicola Maher (MPI-M) and Jochem Marotzke (MPI-M).

Decision makers express a need for reliable information on changes in climatic extremes in the coming decades. However, projections at these time scales involve large irreducible uncertainties due to internal variability. I will demonstrate that despite large uncertainties at local scale, projections in an aggregated spatial perspective are consistent even for the coming decades. Furthermore, models agree reasonably well on the forced response of temperature and heavy precipitation extremes, the pattern of change in the absence of internal variability. Thus, I argue that it is vital to specify whether model agreement refers to the forced response or for individual realization. However, ultimately our confidence in changes of extremes does not only depend model agreement but the consistency between different lines of evidence — the combination of process understanding, agreement across a hierarchy of models and the wealth of observational evidence.

                                                                                                                                                                               

December 6th | Alexis Hannart, Ouranos, Montreal, Canada

Climate change and causal attribution: an overview

Alexis Hannart is guest of Sebastian Sonntag (MPI-M).

Have human emissions been the dominant cause of the observed climate warming? Extremely likely so of course (IPCC, AR5) but what is this statement based upon? And also, what about last summer’s European heatwave? And the wildfires recently affecting western North America, are they also attributable to human influence? How certain are we? And what about the Montreal flood of spring 2017? And the progression of the Lyme disease in some regions? And the trend in agricultural yields? And the hurricane Florence hitting North Carolina last September? And so on.
 
Such causal questions are more and more frequently asked to scientists by various sectors of society. Answers partly condition adaptation measures, mitigation policy as well as legal liability. How does science approach them? This seminar will attempt to give an overview of this question.

                                                                                                                                                                              

January 24th | Stefan Kollet, FZ Jülich

Groundwater-to-atmosphere simulations including human water use: sustainability concepts revisited

Stefan Kollet is guest of Bjorn Stevens (MPI-M).

Groundwater-to-atmosphere simulations are useful for closing the terrestrial water and energy cycles at the continental scale and interrogating anthropogenic impacts at different space and time scales.  We want to understand how human water use, in this case groundwater pumping and irrigation, changes the natural terrestrial cycles over the  European continent including local effects, such as changes in water table depths, evapotranspiration, and air temperature, and non-local effects, such as base flow, continental discharge and precipitation. In particular, we study whether these changes are systematic in space and time, and ultimately impact and potentially redistribute water resources across the continent. We present technical aspects of our work related to model coupling and high-performance computing technologies, and results illustrating the significant impact of human water use beyond individual watersheds.

                                                                                                                                                                              

January 31st | Alberto Garabato, University of Southampton

The power of the small: The emergent role of submesoscale turbulence in shaping ocean circulation and climate 

Alberto Garabato is guest of Jochem Marotzke (MPI-M).

Submesoscale turbulence is made up of oceanic currents with horizontal scales on the order of 1 km and time scales similar to an inertial period. This class of ocean flows has been traditionally ignored, because it is often less energetic than other types of ocean currents, and because it has only just started being partially resolved by some ocean circulation models in the last few years. In this talk, I will argue that submesoscale turbulence is important in shaping ocean circulation in key places at the ocean’s boundaries, where the ocean interacts with other elements of the climate system. To do this, I will draw on three recent observational experiments at the ocean’s interface with the atmosphere, the cryosphere and the Earth’s topography – and show that, in all three cases, submesoscale turbulence governs a significant aspect of the ocean’s climatic role.

April 18th | Adam Scaife, Met Office, UK

Seasonal predictability of the winter North Atlantic Oscillation

Adam Scaife is guest of Johanna Baehr (Uni HH).

The last few winters continue to suggest that the winter NAO and hence winter average weather over large areas of Europe is predictable at seasonal lead times with a good level of correlation skill.   I will show mechanisms for this predictability and argue that it originates from predictable variations in tropical rainfall and initial conditions in the stratosphere.  High predictability of tropical rainfall is first demonstrated for current prediction systems and this is shown to lead to predictable changes in seasonal vorticity sources.  These are associated with stationary Rossby waves that propagate polewards and eastwards into the extratropics, including the Atlantic sector, where the connection to tropical rainfall can explain around half of the forecast variance in the NAO.  We also show that initial atmospheric conditions are important for seasonal prediction of the NAO.  Initial anomalies in stratospheric winds at the start of winter propagate downwards into the troposphere where they lead to anomalies in the winter mean surface conditions.  Together, these mechanisms may explain the majority of forecast variance in the winter NAO.  Finally, we discuss some of the remaining errors in these ensemble forecasts, including the unresolved signal-to-noise paradox which means that current seasonal forecasts are better at predicting the real world than they are at predicting their own forecast members.

Unfortunately, no recording could be made due to technical difficulties.

                                                                                                                                                                               

May 9th | Alexander Proelß, Juristische Fakultät, Uni Hamburg

International Environmental Law and the Challenge of Climate Change

Alexander Proelß is guest of Hauke Schmidt

In view of the epochal challenges of climate change, international environmental law stands at a crossroad. Current regulatory principles and strategies mostly focus on the protection of individual environmental goods and are often distinguished by their fragmentary, or general, character. This also applies for the 2015 Paris Agreement, which pursues the aim of halting the increase in the global average temperature to well below 2°C above pre-industrial levels, and of pursuing efforts to limit the temperature increase to 1.5 °C above pre-industrial levels. Notwithstanding all efforts that have been taken so far, it seems highly questionable whether this objective can be achieved by the present (but partly unsuccessful) attempts to drastically reduce global carbon dioxide emissions. Against this background, international environmental law will also have to address the implementation of supplementary (“secondary”) climate measures in future. This does not only imply the need to improve the implementation and enforcement of the law as it stands today, but also to develop it further in order to provide an effective as well as legitimate normative answer to the “grand challenges” of international environmental politics.

                                                                                                                                                                               

May 23rd | Amanda Maycock, University of Leeds, UK

ENSO teleconnections to the extratropics: role of El Niño amplitude and seasonal cycle

Amanda Maycock is guest of Jochem Marotzke (MPI-M).

ENSO is a key driver of interannual climate variability in many regions of the world. However, disentangling the dependence of ENSO teleconnections on the specific characteristics of events is challenging given the relatively small number of observed events and multiple sources of internal variability.

In this talk I will present recent work from my group using targeted climate model experiments to investigate the mechanisms underpinning ENSO teleconnections to two extratropical regions spanning both hemispheres: the North Atlantic and the Amundsen sea low. I will focus on how the tropical-extratropical teleconnections vary as a function of ENSO amplitude and the role of the seasonal cycle.

In contrast to some previous studies, we show that the influence of El Niño on the winter North Atlantic Oscillation (NAO) is approximately linear over the range of observed El Niño amplitudes. The NAO response is tied to a weakening of the stratospheric polar vortex and an increase in the frequency of major sudden stratospheric warmings. In the Southern hemisphere, the El Niño teleconnection to the Amundsen Sea region is largest in austral winter, despite the fact El Niño typically peaks in austral spring/summer. In austral winter, the region of strong absolute vorticity near ∼30°S provided by the subtropical jet, in combination with the changes to upper tropospheric divergence due to the El Niño perturbation, acts as an anomalous Rossby wave source that is largely absent in austral summer. Furthermore, in austral summer the poleward propagation of tropically-sourced Rossby waves into the Amundsen sea region is inhibited by the strong polar front jet in the south Pacific sector, which leads to Rossby wave reflection away from the Amundsen sea region.

I will conclude by giving some ideas for key outstanding questions in understanding ENSO teleconnections to the extratropics.

                                                                                                                                                                               

[CANCELLED]June 13th | Trude Storelvmo, University of Oslo, Norway

State-dependent cloud feedbacks make equilibrium climate sensitivities > 5°C plausible

Trude Storelvmo is guest of Jochem Marotzke (MPI-M).

For decades, global climate models (GCMs) have produced equilibrium climate sensitivities (ECSs) between 2 and 4.5°C, but interestingly that is now about to change: a subset of state-of-the-art GCMs participating in the 6th coupled model intercomparison project is producing ECSs well above 5°C. Here, I present analyses based on one such high-ECS model. In the past, it has been assumed that such very high simulated ECSs would make it practically impossible for GCMs to reproduce the historical temperature record, but that turns out not to be the case. This is because the model in question has a net positive cloud-climate feedback that grows with warming – in other words: the warmer it gets, the more clouds change in a way that further amplifies the warming, while for modest warming the amplification is much smaller. In this presentation I will explain the underlying physical mechanism responsible for the simulated state transition and discuss its general validity and broader implications.

                                                                                                                                                                               

June 20th | Julia Pongratz, University of Munich

Managing climate by managing land

Julia Pongratz is guest of Martin Claußen (MPI-M).

Three quarters of the ice-free land surface are under some form of land use — cleared for agriculture, grazed on, or used in forestry. Strong further changes are expected for the future, because land use has been assigned a prime role in the effort to limit global warming to 2 degrees. Recent years have seen a surge in Earth observations focused on land use effects on climate. But observations often disagree with model results, preventing trust in model projections. For example, changes in energy and water fluxes associated with a reduction in forest cover show warming in most regions in observations, but cooling in Earth system models. Further, carbon stocks and fluxes associated with historical land use change are generally larger in observations than in models. In this presentation I resolve these discrepancies, highlight the dual role of land use as adaptation and mitigation tool, and prove the need to account for land management in addition to land cover changes in climate and carbon cycle modeling.

This event was not recorded.

April 5th |Pierre Gentine, Department of Earth and Environmental Engineering, Columbia University

What do we need to know about weather and climate extremes in a warming world?

Pierre Gentine is a guest of Cathy Hohenegger (MPI-M).

With rising CO2 concentration, the continental hydrological and carbon dioxide cycles are going to become more coupled. Predicting whether we will live in a drier or wetter world, with more or less droughts, is a relatively simple question, which has however widespread implications. Yet, we are not in a position to clearly answer this simple question. Models predict that surface CO2 physiological effects will dominate the future continental hydrological cycle. Those effects appear critical to explain whether we will live in a drier or wetter world...

                                                                                                                                                                               

April 12th | Oliver Geden, German Institute for International and Security Affairs (SWP), Berlin - (Guest Researcher at the MPI-M and the CGG from April – October 2018)

The challenge of integrating carbon dioxide removal into the EU's climate policy paradigm

Oliver Geden is a guest of Jochem Marotze (MPI-M).

Scenarios meeting the Paris Agreement’s temperature targets envisage a major and imminent deployment of technologies to remove carbon dioxide from the atmosphere, of which there has been almost no practical implementation to date. The talk explores the political dimensions and policy implications of expectations for ‘negative emissions’ in the European Union, considering its largely successful leadership role in mitigation action and corresponding low-carbon technology development and deployment...

                                                                                                                                                                               

April 19th |Christian Beer, Bolin Centre for Climate Research, Stockholm University

Importance of temporal and spatial variability of environmental conditions for land-atmosphere interactions in permafrost landscapes

Christian Beeris a guest of Victor Brovkin (MPI-M).

Northern permafrost soils are a huge reservoir of carbon that has been accumulated during the Pleistocene and Holocene. Climate-change induced permafrost thawing will make this carbon available for decomposition, initiating a positive feedback mechanism. However, future projections of high-latitude greenhouse gas balances remain highly uncertain. This talk will review recent advancements of our understanding of vegetation and soil carbon turnover processes with a special focus on the production of methane versus carbon dioxide...

                                                                                                                                                                               

April 26th | Sharon Nicholson from the Department of Earth, Ocean & Atmospheric Science, Florida State University

The myth of the ITCZ over equatorial Africa and other myths concerning African climate

Sharon Nicholson is guest of M. Claußen (MPI-M).

African climate is frequently a topic of discussion because of the devastating droughts that affect much of the continent.  Much of the discussion is in the lay press and rumors abound. Unfortunately, many have been believed by the scientific community and get repeated in journal articles.  This talk exposes some of the myths and makes the more serious claim that issues concerning the ITCZ should be included in the category of "myths".  The common explanation for the progression of the rainy season over Africa is the seasonal excursion of the ITCZ. The ITCZ paradigm stems from a time when tropical rainfall was assumed to be associated mainly with localized convection. Its development was also linked to the emergence of mid-latitude frontal concepts. The paradigm has numerous shortcomings, including the diversity of definitions and the large number of parameters used to identify the ITCZ...

                                                                                                                                                                               

May 3rd |Pierre Friedlingstein, University of Exeter

Pierre Friedlingstein is a guest of Victor Brovkin (MPI-M).

 The terrestrial carbon cycle plays a central role in the climate system. On the average, about 30 % of the anthropogenic emissions of CO2 are being absorbed by terrestrial ecosystems, the rest being taken by the ocean or remaining in the atmosphere and contributing to climate change. The land carbon sink is a complex combination of ingoing and outgoing natural fluxes (photosynthesis, respiration, fires, etc) as well as fluxes from land use changes. These processes are being affected by changes in environmental drivers, atmospheric CO₂ being probably the main driver of land sink, modulated by climate, nutrient limitation..

                                                                                                                                                                               

May 17th |David Tyfield, Lancaster Environment Centre, Lancaster University

David Tyfield is guest of Anita Engels (Universität Hamburg).

Will Chinese (E-mobility) Innovation Lead in Global Low-Carbon Transition?

In the last couple of years, however, an alternative future has emerged into global consciousness, regarding a new and unlikely hero for global environmental challenges in the 21st century: China.  China’s severe environmental challenges, including those of GHG emissions and air pollution, have long had negative international public attention.  But more recently, spectacular developments in a number of domains of low-carbon technology have begun to seed a new celebratory narrative.  This sees Chinese low-carbon innovation as an exceptional force that will both continue an apparently exponential rate of improvement while simultaneously spreading rapidly around the world with unrivalled government support.  In short, China’s national project of ‘Ecological Civilization’, it is argued, may yet ‘save the planet’.
This talk will explore evidence from the key arena of urban mobility innovation – arguably the ‘hardest case’ for low-carbon transition and one in which the new narrative is particularly significant.  We will explore the confusing dynamics of low-carbon innovation China and how they illuminate profound social and (geo-) political changes that are taking place in parallel with the rise of Chinese environmental technologies… and which must be taken into account when forecasting their possible future impact, both environmentally and socially.

                                                                                                                                                                               

May 31st | Benjamin Murray, University of Leeds

Benjamin Murray is guest of Bjorn Stevens (MPI-M).

The Seeds of Ice in Clouds

The formation of ice in clouds is fundamentally important to life on our planet since cold clouds play a central role in climate and the hydrological cycle. Despite the significance of ice formation, our quantitative understanding of sources, properties, mode of action and transport of Ice-Nucleating Particles (INP) is remarkably poor. In this seminar I will review some of the advances we have made over recent years, focusing on improving knowledge of mineral dust INPs from deserts through laboratory and modelling work as well as using aircraft and ground stations on either side of the tropical Atlantic. As part of this, I will illustrate how we cross scales from laboratory research where we can identify nanoscale ice nucleation sites through to planetary scale modelling of INP and interaction with cloud fields... 

This talk was not recorded.

                                                                                                                                                                               

June 21st | Sarah Kang, Ulsan National Institute of Science and Technology, Korea

Sarah Kang is a guest of Bjorn Stevens (MPI-M).

Distinct tropical climate response to subpolar energy perturbations from the Northern or Southern Hemisphere

The energetics framework predicts how climatic asymmetry develops in response to interhemispheric differences in energy flux into the coupled ocean-atmosphere system. Indeed, the late 20th century anthropogenic aerosol emissions, mostly concentrated in the Northern Hemisphere (NH), forced an interhemispheric Hadley circulation that displaces the Inter-Tropical Convergence Zone (ITCZ) southward. Confusions arise, however, from recent climate model experiments that utilize realistic dynamical oceans, in which radiative perturbations over the Southern Ocean fail to significantly displace the ITCZ. Using a hierarchy of coupled models, here we demonstrate a previously unrecognized sensitivity that the tropical response is intrinsically distinct depending on whether the subpolar energy perturbation comes from the NH or Southern Hemisphere (SH)...

                                                                                                                                                                               

July 12th | Douglas Maraun, Karl-Franzens-Universität, Graz

Douglas Maraun is guest of Hermann Held (Universität Hamburg).

Understanding regional weather extremes in a changing climate

Regional weather extremes often have severe impacts on society and ecosystems. There is evidence that the character of events such as heatwaves or heavy precipitation has been changing already in response to anthropogenic global warming, and will continue to change. Yet our ability to simulate these changes is limited. In particular regional information about future extremes is affected by substantial uncertainties. These uncertainties stem from mainly four sources: internal climate variability fundamentally limits the signal to noise ratio of climate projections, in particular at the regional scale. Current generation general circulation models have too coarse a resolution to realistically represent large-scale circulation features associated with extreme events, and their response to climate change... 

November 2nd | Ben Marzeion, University of Bremen

Future sea-level change from past glacier mass loss commitments

Ben Marzeion is a guest of Martina Neuburger (CEN)

Even though glaciers store less than 1% of the global ice mass, they have probably been the strongest contributor to sea-level change in the 20th century. While mass loss from the ice sheets and thermal expansion of the ocean water are quickly increasing, glaciers will continue to play an important role in sea-level change in the 21st century. Understanding the causes, mechanisms and time scales of glacier change is therefore of paramount importance for identifying successful strategies for mitigation of, and adaption to, climate change...

                                                                                                                                                                               

November 9th |Jana Sillmann, CICERO Center for International Climate Research, Norway

What do we need to know about weather and climate extremes in a warming world?

Jana Sillmann is a guest of Detlef Stammer (CEN)

One of today’s major challenges in climate sciences is how to use our state-of-the-art models and climate system knowledge to inform decision making regarding societal responses to climate change. Among the five key reasons for concern, according to the Intergovernmental Panel on Climate Change (IPCC), are the risks from weather and climate extremes. Severe impacts could be prevented or alleviated through appropriate adaptation measures and better preparedness. Weather and climate extremes are influenced by a complex interplay of natural and anthropogenicfactors that determine their occurrence, frequency, and intensity. Adaptation planning is challenged to take into account near- and long-term variability and changes in weather and climate extremes and associated uncertainties...

This talk was not recordet.

                                                                                                                                                                               

November 16th | Andy Pitman, University of New South Wales, ARC Centre of Excellence for Climate System Science, Australia

Drought in climate models: what can we do about the uncertainty in climate projections?

Andy Pitman is a guest of Martin Claußen and Victor Brovkin (MPI-M).

There is no agreement on how best to define droughts. They can occur over multiple temporal and spatial scales with significant Australian droughts lasting a decade. We name them in Australia: the Federation Drought, the World War II drought, the Millennium Drought and they are written into our music, literature and poetry. No CMIP5 climate model simulated an event with the duration of the Millennium Drought; there is something missing in the models in terms of the large-scale forcing. In uncoupled simulations, land surface schemes tend to dry too quickly, and remain dry too long in comparison to observations. In short, CMIP5 simulations of long-term/large scale forcing and seasonal/regional scale forcing are inconsistent with observations. Projections of future interannual droughts are uncertain to a degree that the sign of the change in future drought is unknown reliably... 

                                                                                                                                                                               

November 23rd |Piotr Smolarkiewicz,ECMWF, UK

A finite-volume module for cloud-resolving simulations of global atmospheric flows

Piotr Smolarkiewicz is a guest of Peter Korn (MPI-M)

The talk highlights the development of the Finite-Volume Module (FVM) of the Integrated Forecasting System (IFS) at ECMWF. FVM represents an alternative dynamical core that enhances the spectral dynamical core of the IFS with new capabilities, such as a compact-stencil finite-volume discretisation, flexible meshes, conservative non-oscillatory MPDATA transport, and all-scale nonhydrostatic governing equations...

This talk was not recordet.

                                                                                                                                                                               

November 30th | Kirstin Krüger, University of Oslo, Norway

Does the ocean impact the ozone layer?

Kirstin Krüger is a guest of Hauke Schmidt (MPI-M)

Natural, halogenated very short-lived substances (VSLS) with an atmospheric lifetime τ<0.5 yr play an important role in the stratospheric ozone budget besides the anthropogenic long-lived chlorine- and brominefluorocarbons. The tropical oceans are a known source of reactive iodine and bromine to the atmosphere such as the VSLS methyl iodide (CH3I), bromoform (CHBr3), and dibromomethane (CH2Br2). They contribute to the halogen loading of the stratosphere if they are transported fast enough within, i.e., deep tropical convection. The tropical West Pacific and Indian Ocean are of special interest since the oceanic compounds of the VSLS are projected to have hot spots for both their emissions and transport pathways to the stratosphere. This study will give an overview of 10 years of research work on VSLS sources in the tropical oceans and their transport pathways and contribution to the stratospheric halogen level to answer the question.

                                                                                                                                                                               

December 14th |Roda Verheyen, Rechtsanwälte Günther, Hamburg

Climate change impacts – the role of the law: who is liable?  The example of the case Lliuya ./. RWE

Roda Verheyen is a guest of Martin Claußen (MPI-M)

In this talk, lawyer Dr. Roda Verheyen will present the case of the Peruvian farmer Saúl Luciano Lliuya who took legal action against the energy company RWE. In his lawsuit he argues that Lake Palcacocha which is located above his hometown Huaraz in the Andes is at risk to “spill over” caused by glacier melting. In such a case his property would be damaged. Lliuya claims that this melting is caused by climate change which in turn RWE has contributed to through its operations. To protect his house, Lliuya has already invested in appropriate safety precautions. He now requests RWE to cover parts of his expenses – proportionate to RWE’s level of impairment.

                                                                                                                                                                               

January 18th |Friederike Otto, University of Oxford, Environmental Change Institute, UK

Changing climate hazards across timescales

Friederike Otto is a guest of Detlef Stammer (CEN)

Increasing risks of extreme weather events are the most noticeable and damaging manifestation of anthropogenic climate change. In the aftermath of an extreme event, policymakers are often called upon to make timely and sensitive decisions about rebuilding and managing present and future risks. Information regarding whether, where, and how present day and future risks are changing is needed to adequately inform these decisions. But this information is often not available and when it is, it is often not presented in a systematic way. A seamless approach to extreme event attribution and future risk assessment using the same set of model ensembles could be used to provide such information on past, present and future hazard risk...

                                                                                                                                                                               

January 25th |Laurent Bopp, LSCE, IPSL, France

The ocean carbon sink, today and tomorrow

Laurent Bopp is a guest of Tatiana Ilyina (MPI-M)

The ocean is currently absorbing one quarter of all anthropogenic carbon emissions due to fossil fuel combustion and deforestation, thus significantly limiting the pace of increasing atmospheric CO₂ and anthropogenic climate change. For the next decades, ocean models indicate that ocean carbon uptake will continue under all scenarios to 2100 (very high confidence, IPCC, 2013). There is also high agreement between models that climate change, through ocean warming and circulation changes, will partially offset this increase caused by rising atmospheric CO₂.

Yet, there are still some severe inconsistencies between model simulations and carbon cycle observations over the last decades, very large regional differences in future projections performed with ocean carbon cycle models, and important processes that are still missing in the models. In this presentation, I review some of these shortcomings and present some on-going work aiming at resolving these issues, focusing on (1) unrepresented processes related to marine ecosystems, (2) the contribution of coastal ocean processes, and (3) the potential large variability in air-sea carbon fluxes, as shown by observations and underestimated by ocean models.

                                                                                                                                                                               

February 1st | Kevin Heng, University of Bern, Center for Space and Habitability

Remote Sensing of Exoplanetary Atmospheres

Kevin Heng is a guest of Bjorn Stevens (MPI-M).

Short of interstellar travel, understanding the nature of exoplanets and potential habitats beyond the Solar System must necessarily proceed via remote sensing.  Specifically, the problem reduces to measuring and interpreting spectra of exoplanetary atmospheres, which is currently one of the frontier topics in astronomy and astrophysics.  The specific format of the data measured implies that the traditional methods of the Earth and planetary sciences cannot be imported without modification and generalisation.  In the current talk, I will focus on the physics of radiative transfer concerning transmission spectroscopy, which quantifies the variations in the amount of starlight occulted by an exoplanet, across wavelength, due to the varying opacity of its atmospheric constituents.

April 6th | Ken Caldeira, Carnegie Institution for Science, Stanford

Coral reefs, ocean acidification, and transformation of the global energy system

This talk will discuss our recent field work in Australia’s Great Barrier Reef in the ocean, acidification in the broader context of the global climate system, and the need for the development of near-zero emission global energy and transportation systems.

We have conducted the first-ever experiments in which a plume of water with high carbon dioxide concentrations was allowed to flow over a natural coral reef community without any artificial confinement. Our preliminary results indicate that the carbon dioxide harmed coral reef growth by increasing the rate of dissolution of the calcium carbonate minerals that make up much of the coral reef...

                                                                                                                                                                               

April 13th | Chris Bretherton, University of Washington

Insights from high-resolution simulation of cloud feedbacks

Cloud feedbacks are a leading source of uncertainty in the climate sensitivity simulated by global climate models (GCMs). Low-latitude boundary-layer and cumulus cloud regimes are particularly problematic, because they are sustained by tight interactions between clouds and unresolved turbulent circulations.This talk reviews cloud feedbacks simulated by high-resolution models that simulate the dominant cloud-forming eddy motions in such regimes..

                                                                                                                                                                               

April 20th | David Keith, Harvard University

Assessing and Reducing the Risks of Solar Geoengineering

I will discuss new results suggesting it may be possible to implement solar geoengineering using stratospheric aerosols without ozone loss while significantly reducing some other important side effects....

                                                                                                                                                                               

May 4th | Carl Friedrich Gethmann, Universität Siegen

This talk was held in German.

Einige wissenschaftsphilosophische Fragen zur epistemischen Qualitätssicherung von Klimamodellen

Die Herausforderungen der Menschheit durch „kollektive Handlungsprobleme von globalem Zuschnitt“, zu denen neben einer Reihe von anderen auch die Folgen der anthropogenen Erderwärmung gehören, erfordern einen neuen Typ von Wissenschaft, der unter unterschiedlichen Stichwörtern schon mehrfach beschrieben worden ist. Dabei steht die Wissenschaft unter besonderen Bedingungen des Nichtwissens (durch Ungewißheit, Unsicherheit und systematische Beschränktheit), die eine besondere methodologische Sorgfalt bei der Hypothesenbildung erfordern...

                                                                                                                                                                               

May 11th | Kaoru Sato, University of Tokyo

An interplay of Rossby waves and gravity waves in the general circulation of the middle atmosphere

The meridional circulation of the middle atmosphere is maintained by angular momentum deposition associated with waves. The summer-to-winter circulation in the mesosphere is mainly driven by gravity-wave forcing (GWF). However, GWF is not uniformly distributed, reflecting source distribution and filtering by Rossby waves...

This talk was not recorded. 

                                                                                                                                                                               

May 18th | Dania Achermann, University of Aarhus

Changing Cultures of Climate Understanding: A historical perspective on climate modelling

Today, climate research is dominated by the use of computer models. Introduced in the 1950s and 60s they have since gained high epistemic authority in producing climate knowledge. As this talk will show, the emergence of climate modelling as a hegemonic research tool and the shaping of modern climate science was not a linear development but a result of a competition between various approaches from different disciplines and “cultures” within climate research...

                                                                                                                                                                               

June 15th | Georg Kaser, University of Innsbruck

Glaciers under climate change

Slide no. 11 had to be deleted since it has not been published yet.

There are approximately 200.000 individual glaciers globally, scattered from low-latitude high mountains to high-latitude islands and to the fringes of the ice sheets. Each one adapts to changing climate conditions individually, not only causing effects of different kind and magnitude but also telling different stories about the drivers for their change... 

                                                                                                                                                                               

June 22th | Robert J. Nicholls, University of Southampton, UK

Climate change and sea-level rise: impact and adaptation on the coast

Global mean sea-level rise is resulting in a range of impacts including increased flood risk and submergence, salinisation of surface and ground waters, and morphological change, such as erosion and wetland loss. The potential human and ecosystem impacts in the 21st Century are significant but uncertain. Actual impacts will depend on a range of change factors in addition to the amount of sea-level rise and climate change, including a number of factors which are human-controlled such as coastal land use and management approaches...

                                                                                                                                                                               

June 29th | Toshiro Tanimoto, University of California, CA

Seismic and acoustic waves in the whole Earth system

Our study of the Earth has been compartmentalized by traditional disciplines such as atmospheric science, ocean science, and solid-earth science. However, seismic and acoustic waves refract and propagate through the whole Earth system, not being confined to any one of the medium..