For the open session, we welcome contributions on all aspects of ocean circulation from observations, models and theory, from regional to global scales, from air-sea exchanges to abyssal mixing. This year our session will include the Fridtjof Nansen medal award lecture, by Anne-Marie Treguier. We particularly encourage studies on the interannual to decadal variability and the internal and externally forced physical processes in the ocean. Because accurate estimation of energy and mass fluxes is critical for the closure of the ocean energy budget and the ocean's impact on the atmosphere, this session also welcomes works dealing with processes at the ocean's boundaries. This includes studies focusing on the fundamentals of air-sea flux physics, on the ocean's interaction with the cryosphere, as well as on the physical processes occurring at topographic boundaries. As usual the OS1.1 session also welcomes submissions that do not fit to any of the other special sessions; this includes the oceanography of the Pacific Ocean.

The rapid decline of Arctic sea ice in the last decade is a dramatic indicator of climate change.  The last 12 years have seen lower Arctic summer sea ice extents than in the previous 29 years of satellite records. The Arctic sea ice cover is now thinner, weaker and drifts faster. The ocean is also changing, the volume of freshwater stored in the Arctic and has increased as have the inputs of coastal runoff from Siberia and Greenland. Concurrently inflows from the Atlantic and Pacific Oceans have warmed. As the global surface temperature rises, the Arctic Ocean is speculated to become seasonally ice-free in the 21st century, which prompts us to revisit our perceptions of the Arctic system as a whole. What could the Arctic look like in the future? How are the present changes in the Arctic going to affect the lower latitudes? What aspects of the changing Arctic should future observations and modelling programs address? The scientific community is investing considerable effort in organising our current knowledge of the physical and biogeochemical properties of the Arctic, exploring poorly understood coupled atmosphere-sea-ice-ocean processes to improve prediction of future changes in the Arctic.
 
In this session, we invite contributions on a variety of aspects of past, present and future climates of the Arctic. We encourage submissions addressing interaction between ocean, atmosphere and sea ice and on studies linking changes in the Arctic to the global ocean. Submissions with a focus on emerging cryospheric, oceanic and biogeochemical processes and their implications are particularly welcome. The session promotes results from current Arctic programmes and discussions on future plans for Arctic Ocean modelling and measurement strategies. This session is cosponsored by the CLIVAR /CliC Northern Ocean Regional Panel (NORP) that aims to facilitate progress and identify scientific opportunities in (sub)Arctic ocean-sea-ice-atmosphere research.

The North Atlantic exhibits a high level of natural variability from interannual to centennial time scales, making it difficult to extract trends from observational time series. Climate models, however, predict major changes in this region, which in turn will influence sea level and climate, especially in western Europe and North America. In the last years, several projects have been focused on the Atlantic circulation changes, for instance OVIDE, RACE, OSNAP, and ACSIS. Another important issue is the interaction between the atmosphere and the ocean as well as the cryosphere with the ocean, and how this affects the climate.
We welcome contributions from observers and modelers on the following topics:

-- climate relevant processes in the North Atlantic region in the atmosphere, ocean, and cryosphere
-- response of the atmosphere to changes in the North Atlantic
-- atmosphere - ocean coupling in the North Atlantic realm on time scales from years to centuries (observations, theory and coupled GCMs)
-- interpretation of observed variability in the atmosphere and the ocean in the North Atlantic sector
-- Comparison of observed and simulated climate variability in the North Atlantic sector and Europe
-- Dynamics of the Atlantic meridional overturning circulation
-- variability in the ocean and the atmosphere in the North Atlantic sector on a broad range of time scales
-- changes in adjacent seas related to changes in the North Atlantic
-- role of water mass transformation and circulation changes on anthropogenic carbon and other parameters
-- linkage between the observational records and proxies from the recent past

Invited Speakers: Professor Ric Williams, University of Liverpool, UK
Dr. Arnaud Czaja, Imperial College, London, UK

The climate state of the Atlantic Ocean is known to exert a huge control and hence a decisive role on the surface climate over the neighbouring continents as well as that of the Arctic Ocean. Heat in the South Atlantic converges from both the Pacific and Indian Oceans and is carried northward to higher latitudes along the dynamically-rich oceanic current systems to key deep water formation regions where the atmosphere is in direct contact with the deep ocean. Understanding what drives the variability of the Atlantic Ocean on multiple time scales and long-term trends is thus imperative for more confident predictions of the climate in the future decades.

This session will offer the opportunity to focus on the dynamics, variability and trends along the key climatic current systems from the South Atlantic to the North Atlantic and into Arctic Ocean and how they are influenced by local-, large- or global-scale processes or teleconnections. We aim to bring together researchers using observations, ocean models and state-of-the-art climate models.

We welcome presentations addressing:

- Sources, dynamics, pathways and meridional connectivity of heat and freshwater anomalies from lower to higher latitudes
- Impact of large- and global-scale atmospheric modes on Atlantic Ocean circulation
- Variations and long-term trends in Atlantic overturning circulation and relationship to sea-level and sea-ice change

Invited speaker: Penny Holliday, National Oceanography Centre, UK

The Southern Ocean, which stretches from Antarctic ice-shelf cavities to the northern fringe of the Antarctic Circumpolar Current, is a key region for water mass formation and for the uptake, storage and lateral exchanges of heat, carbon and nutrients. At present, the Southern Ocean acts as a sink of anthropogenic carbon and heat and as a source of natural carbon, but its role in future climate conditions remains uncertain. Processes on the Antarctic continental shelf also need to be better understood in order to assess the ocean’s role in Antarctic ice loss and the resulting meltwater impact on sea level. To reduce these uncertainties, it is critical to investigate the mechanisms underlying Southern Ocean's internal variability and its response to external forcing. Recent advances in observational technology, data coverage, circulation theories, and numerical models are providing a deeper insight into the three-dimensional patterns of Southern Ocean change. This session will discuss the current state of knowledge and novel findings concerning Southern Ocean circulation, water mass formation and pathways, mixing and mesoscale dynamics, ocean-ice-atmosphere interactions, sea ice changes, inflow of warm water to ice shelf cavities, and biological productivity, as well as the heat, nutrient and carbon budgets. This includes work on all spatial scales (from local to basin-scale to circumpolar) and temporal scales (past, present and future). We particularly invite cross-disciplinary topics involving physical and biological oceanography, glaciology, or biogeochemistry.

The seasonal reversal of monsoon winds and concurrent ocean currents, relatively deep thermocline along the equator due to the lack of steady easterlies, low-latitude connection to the neighboring Pacific and a lack of northward heat export due to the position of the Asian continent make the Indian Ocean unique among the other tropical ocean basins. These characteristics shape the Indian Ocean’s very dynamic intraseasonal, seasonal, and interannual variability, as well as its air-sea interactions. They also make the basin and its surrounding regions, which are home to a third of the global population, particularly vulnerable to anthropogenic climate change, and robust warming and trends in heat and freshwater fluxes have been observed in recent decades. Advances have recently been made in our understanding of the Indian Ocean’s circulation, interactions with adjacent ocean basins, and its role in regional and global climate. Nonetheless, significant gaps remain in understanding, observing, modeling, and predicting Indian Ocean variability and change across a range of timescales.

This session invites contributions based on observations, modelling, theory, and palaeo proxy reconstructions in the Indian Ocean that focus on understanding and predicting the links between Indian Ocean variability and monsoon systems on (intra)seasonal to interannual timescales, interactions and exchanges between the Indian Ocean and other ocean basins, decadal variability and its prediction, response to climate change, extreme events, as well as interactions between physical, biogeochemical, and ecological processes. Contributions are also sought that address research on the Indian Ocean grand challenges, as formulated by the Climate and Ocean: Variability, Predictability, and Change (CLIVAR), the Sustained Indian Ocean Biogeochemistry and Ecosystem Research (SIBER), and the International Indian Ocean Expedition 2 (IIOE-2) programs.

Observations and simulations of ocean circulation and marine atmosphere processes are rapidly growing for meso to basin scale, on diurnal to interannual scale. This session focuses on tropical and subtropical ocean dynamics as well as local interaction between the ocean and the overlying atmosphere from the equator to mid-latitudes. Relevant processes in the ocean include upper and deep ocean circulation variability, mild SST gradients to sharp fronts, eddies, filaments, tropical instability waves, warm pools, upper ocean various layers, cold tongues and eastern boundary upwelling. Regarding air-sea interactions, we seek studies that analyse the local to regional scales, and those discussing the conditions under which they may lead to a large-scale atmospheric response. Surface wind modulations, Madden-Julian Oscillation, cyclones, and convective systems, as well as scale interactions are welcome. In the extra-tropics, we seek also contributions on the role of extra-tropical fronts in regional and large-scale atmospheric circulation. We welcome contributions on how the air-sea interactions may shape modes of climate variability and determine regional climate sensitivity.

Highly productive Eastern Boundary Upwelling Systems (EBUS) play a key role in the global carbon and nitrogen cycles. They also sustain intense fishery activities that could be affected by climate change. EBUS are characterized by a complex interplay of biological, chemical and physical processes taking place in sediments, water column and at the air-sea interface. In particular, physical processes range from regional scales to mesoscale eddies, submesoscale filaments and fronts, down to internal waves and microscale turbulence. They drive the transport of solutes such as nutrients, carbon and oxygen, as well as particulate matter and living organisms. A recent improvement in computational power and new techniques such as multi-nesting approaches, made possible to increase the resolution of regional ocean models down to some hundred meters, allowing to resolve these processes on the fine scale. New observational techniques such as airborne, underway, and autonomous technologies allow for high-resolution adaptive multidisciplinary campaigns. Recent progress in biological/microbial techniques and application of new chemical sensor techniques allow deciphering of biogeochemical patterns with unprecedented high resolution.

Interdisciplinary observational and modeling studies investigating physical, biological and chemical aspects of the major EBUS are welcome. In particular studies which combine observational and modeling efforts, new data analysis techniques and focusing on climate change impacts are of interest.

NEWS: We are glad to announce that Monique Messie (https://www.mbari.org/messie-monique/) will give a solicited contribution to our session.

A wide range of processes in the earth system directly affect geodetic observations. This session invites a wide array of contributions which showcase the use of geodesy for Earth science and climate applications, providing crucial insights into the state and change of the earth system and/or understanding its processes.

Data driven quantification of water mass fluxes through boundaries of Earth’s different regions and spheres provides important insights to other geoscience communities and informs model validation and improvement. Changes in regional sea level and ocean circulation are observed by altimetry and gravimetry. Natural and anthropogenic alterations of the terrestrial water cycle lead to changes in river runoff, precipitation, evapotranspiration, and water storage which may cause surface deformation sensed by GNSS stations and InSAR measurements as well as mass/gravity changes observed by satellite/ground gravimetry. Mass changes in the ice sheets and glaciers are detectable by both geometrical and gravimetric techniques. And other novel applications of geodetic techniques are emerging in many fields.

In addition, individual sensor recordings are often affected by high-frequency variability caused by, e.g., tides in the solid Earth, oceans, and atmosphere and their corresponding crustal deformations affecting station positions; non-tidal temperature and moisture variability in the troposphere modifying microwave signal dispersion; rapid changes in the terrestrially stored water caused by hydrometeorologic extreme events; as well as swift variations in relative sea-level that are driven by mass and energy exchange of the global oceans with other components of the Earth system, which all might lead to temporal aliasing in observational records. 

This session invites a wide array of contributions which showcase the use of geodesy for Earth science and climate applications. This session aims to cover innovative ways to use GRACE, GRACE-FO and other low Earth orbiters, GNSS techniques, InSAR, radar altimetry, and their combination with in-situ observations. We welcome approaches which tackle the problem of separating signals of different geophysical origin, by taking advantage of model output and/or advanced processing and estimation techniques. Since the use of geodetic techniques is not always straightforward, we encourage authors to think of creative ways to make their findings, data and software more readily accessible to other communities in hydrology, ocean, cryospheric, atmospheric and climate sciences. With author consent, highlights from the oral and poster session will be tweeted with a dedicated hashtag during the conference in order to increase the impact of the session.

Changes in the Arctic and Antarctic climate systems are strongly related to processes in the boundary layer and their feedbacks with the free troposphere. An adequate understanding and quantification of these processes is necessary to improve predictions of future changes in the polar regions and their teleconnections with mid-latitude weather and climate, including meridional transport of heat, moisture and air pollutants. Processes include atmosphere-ocean-ice (AOI) interactions, such as physical and chemical snow processes (e.g. snow photochemistry), exchange of chemical constituents, sources of aerosol, polynya formation processes, sea ice production and bottom water formation, and cloud formation, which represent key processes for the atmosphere, ocean and the cryosphere. AOI interactions are also triggered by and have feedbacks with synoptic systems and mesoscale weather phenomena such as cold air outbreaks, katabatic winds and polar lows. Associated processes also include the effect of warm air advection and clouds on the surface energy budget and related boundary layer exchanges. Of increasing interest is the study of extremes such as heat waves and storms, but also extreme meridional transport events that can disturb the physical and chemical state of the high latitudes and may have a large impact on ecosystem changes. In addition, Arctic boundary-layer processes play an important role for local Arctic air pollution and for the health and ecosystem impacts thereof. In addition, understanding natural processes including AOI interactions is essential to understand of the background atmosphere to quantify the anthropogenic impacts. Shallow inversions, mostly during winter-time, lead to high air pollutant concentrations. Even though severe air pollution episodes are frequently observed in the Arctic, knowledge on urban emission sources and atmospheric chemical processing of pollution, especially under cold and dark conditions, are poorly understood.

This session is intended to provide an interdisciplinary forum to bring together researchers working in the area of boundary layer processes and high-latitude weather and climate (including snow physics, air/snow chemistry, and oceanography). Cryosphere and atmospheric chemistry processes (the focus of the IGAC/SOLAS activity “CATCH” and the IGAC/IASC activity “PACES”) are highly relevant to this session. We invite contributions e.g. in the following areas:

1. Observations and research on the energy balance, physical and chemical exchange processes, and atmosphere-ocean-ice (AOI) interactions including particle sources.
2. Results from high-elevation sites where similar processes occur over snow and ice.
3. Field programs, laboratory studies and observational studies (including remote sensing).
4. Model studies and reanalyses.
5. Advances in observing technology.
6. External controls on the boundary layer such as clouds, aerosols, radiation.
7. Teleconnections between the polar regions and mid-latitudes resulting in effects related to atmosphere-ice-ocean interactions as well as insights provided by monitoring of water vapor isotopes that shed light on air mass origins.
8. High-latitude urban air quality studies.

Recent years have seen a substantial progress in the understanding of the nonlinear and stochastic processes responsible for important dynamical aspects of the complex Earth system. The Earth system is a complex system with a multitude of spatial and temporal scales which interact nonlinearly with each other. For understanding this complex system new methods from dynamical systems, complex systems theory, complex network theory, statistics and climate and Earth sciences are needed.

In this context the session is open to contributions on all aspects of the nonlinear and stochastic dynamics of the Earth system, including the atmosphere, the ocean and the climate system. Communications based on theoretical and modeling studies, as well as on experimental investigations are welcome. Studies that span the range of model hierarchy from idealized models to complex Earth System Models (ESM), data driven models, use observational data and also theoretical studies are particularly encouraged.

Invited speaker: Cecile Penland (NOAA)

This session aims at bringing together multidisciplinary studies that address the current state of Arctic observing systems, including strategies to improve them in the future. We invite contributions covering atmosphere, ocean, cryosphere and terrestrial spheres, or combinations thereof, by use of remote sensing, in situ observation technologies, and modeling. Particular foci are placed on (i) the analysis of strengths, weaknesses, gaps in spatial/temporal coverage, and missing monitoring parameters in existing observation networks and databases, and (ii) studies describing the development and/or deployment of new sensors or observation platforms that extend the existing observing infrastructure with multidisciplinary measurements. This session will be supported by the EU-H2020 project INTAROS, and welcomes contributions from other pan-Arctic networks (e.g. INTERACT, GTN-P, NEON, ICOS, SIOS, IASOA, AOOS), multi-disciplinary campaigns (e.g. ABoVE, NGEE Arctic, Arctic Ocean 2018, RV Polarstern cruises) or databases.

Ice shelves and tidewater glaciers are sensitive elements of the climate system. Sandwiched between atmosphere and ocean, they are vulnerable to changes in either. The recent disintegration of ice shelves such as Larsen B and Wilkins on the Antarctic Peninsula, current thinning of the ice shelves in the Amundsen Sea sector of West Antarctica, and the recent accelerations of many of Greenland's tidewater glaciers provide evidence of the rapidity with which those systems can respond. Changes in marine-terminating outlets appear to be intimately linked with acceleration and thinning of the ice sheets inland of the grounding line, with immediate consequences for global sea level. Studies of the dynamics and structure of the ice sheets' marine termini and their interactions with atmosphere and ocean are the key to improving our understanding of their response to climate forcing and of their buttressing role for ice streams. The main themes of this session are the dynamics of ice shelves and tidewater glaciers and their interaction with the ocean, atmosphere and the inland ice, including grounding line dynamics. The session includes studies on related processes such as calving, ice fracture, rifting and mass balance, as well as theoretical descriptions of mechanical and thermodynamic processes. We seek contributions both from numerical modelling of ice shelves and tidewater glaciers, including their oceanic and atmospheric environments, and from observational studies of those systems, including glaciological and oceanographic field measurements, as well as remote sensing and laboratory studies.

Global ocean circulation plays a key role in redistributing heat and in setting the oceanic carbon gradients, and thus modulates global climate on centennial to millennial time scales. With the emergence of new methods, greater spatial and temporal paleo-record coverage, and model simulations with numerous tracers, significant improvement has been made in the understanding of past oceanic changes and their impacts on global climate and the carbon cycle. New proxy approaches and increasing geographical coverage fill important gaps in the reconstruction of different ocean states and decrease uncertainty that arises from interpretations based on individual parameters and sites. Similarly, refined model approaches and increased computing capacity allow for the integration of important small- and intermediate scale processes as well as the direct inclusion of proxies in numerical models.

This session welcomes contributions on the role of the ocean circulation in Pleistocene climate and glacial-interglacial climate transitions. This comprises proxy and model assessments of ocean heat and carbon content, circulation strength and other climatic and biogeochemical parameters, including details on their regional variation, given they are relevant for understanding global processes. Furthermore, we encourage contributions of reconstructions that seem contradictory to the prevailing view insofar as their discussion may hint towards processes or pitfalls that are under appreciated and thus potentially important for future research.

ENSO is the dominant source of interannual climate variability in the tropics and across the globe. Understanding ENSO's dynamics, predicting El Niño and La Niña, and anticipating changes in ENSO's characteristics and impacts are thus of vital importance for society. This session invites contributions regarding the dynamics of ENSO, including multi-scale interactions; low frequency, decadal and paleo ENSO variability; ENSO theory; ENSO diversity; ENSO impacts on climate, society and ecosystems; ENSO teleconnections; seasonal forecasting of ENSO; and climate change projections of ENSO. Studies aimed at understanding ENSO in models of a range of complexity are especially welcomed, including analysis of CMIP model intercomparisons.

The millennial-scale variability associated with Dansgaard-Oeschger (D-O) cycles during the last glacial is known to have affected the climate system on a global scale. New high-resolution sediment and ice core proxy records document in increasing detail local and global variability of ice sheets, sea ice, as well as oceanic and atmospheric circulation during the D-O cycles. In addition, insights into the dynamics of the coupled ocean-cryosphere-atmosphere system during the millennial-scale climate cycles are emerging from improved model simulations. Documenting the precise timing and sequence of events in proxy records and capturing the processes responsible for the global pattern of rapid climate changes, which stretch from Greenland to Antarctica, remains a major challenge. However, understanding the underlying dynamics will provide fundamental information on the stability of the global climate system. In this interdisciplinary session, we welcome proxy- and model-based research that tests hypotheses on causes and processes behind the D-O events and helps understanding past, present and future changes to the climate system. The session is hosted by the ERC synergy project ice2ice.

Solicited talks include:
Oeschger medal lecture by Edward Brook, Oregon State University
Marlene Klockmann, Helmholtz-Zentrum Geesthacht Centre
Bradley Markle, University of Washington

To address societal concerns over rising sea level and extreme events, understanding the contributions behind these changes is key to predict potential impacts of sea level change on coastal communities and global economy, and is recognized as one of the Grand Challenges of our time by the World Climate Research Programme (WCRP). To continue this discussion, we welcome contributions from the international sea level community that improve our knowledge of the past and present changes in sea level, extreme events, and flooding, and produce improved predictions of their future changes. We welcome studies on various drivers of sea level change and linkages between variability in sea level, heat and freshwater content, ocean dynamics, land subsidence from natural versus anthropogenic influences, and mass exchange between the land and the ocean associated with ice sheet and glacier mass loss and changes in the terrestrial water storage. Studies focusing on future sea level changes are also encouraged, as well as those discussing potential short-, medium-, and long-term impacts on coastal and deltaic environments, as well as the global oceans.

The Arctic Realm is changing rapidly and the fate of the cryosphere, including Arctic sea ice, glaciers and ice caps, is a source of concern. Whereas sea ice variations impact the radiative energy budget, thus playing a role in Arctic amplification, the Greenland Ice Sheet (GIS) retreat contributes to global sea level rise. Moreover, through various processes linking the atmosphere, ice and ocean, the change in the Arctic realm may modify the atmospheric and ocean circulation at regional to global scales, the freshwater budget of the ocean and deep-water formation as well as the marine and terrestrial ecosystems. The processes and feedbacks involved operate on all time scales and thus require several types of information: satellite and instrumental data, climate models, and reconstructions based on geological archives. In this session, we invite contributions from a range of disciplines and across time scales, including observational data, historical data, proxy data, model simulations and forecasts, for the past climate and the future. The common denominator of these studies will be their focus on a better understanding of mechanisms and feedbacks on short to long time scales that drive Arctic and Arctic-subarctic changes and their impact on climate, ocean and environmental conditions, at regional to global scales, including possible links to weather and climate outside the Arctic.

The Arctic sea ice and high latitude atmosphere and oceans have experienced significant changes over the modern observational era. The polar climate is crucial for the Earth’s energy and water budget, and its variability and change have direct socio-economic and ecological impacts. Thus, understanding high-latitude variability and improving predictions of high latitude climate is highly important for society. Predictability studies indicate that decadal to multi-decadal variations in the oceans and sub-seasonal to multi-year sea ice variations are the largest sources of predictability in high latitudes. However, dynamical model predictions are not yet in the position to provide us with accurate predictions of the polar climate. Main reasons for this are the lack of observations in high latitudes, insufficient initialization methods and shortcomings of climate models in representing some of the important climate processes in high latitudes.
This session aims for a better understanding and better representation of the mechanisms that control high latitude climate variability and predictability in both hemispheres at sub-seasonal to multi-decadal time-scales in past, recent and future climates. Further, the session aims to discuss ongoing efforts to improve climate predictions at high latitudes at various time scales (as e.g. usage of additional observations for initialization, improved initialization methods, impact of higher resolution, improved parameterizations) and potential teleconnections of high latitude climate with lower latitude climate. We also aim to link polar climate variability and predictions to potential ecologocal and socio-economic impacts and encourage submissions on this topic.
This session offers the possibility to present results from the ongoing projects and research efforts on the topic of high-latitude climate variability and prediction, including, but not limited to Year of Polar Prediction (YOPP), and the ARCPATH-project (Arctic Climate Predictions - Pathways to Resilient, Sustainable Societies).

One of the big challenges in Earth system science consists in providing reliable climate predictions on sub-seasonal, seasonal, decadal and longer timescales. The resulting data have the potential to be translated into climate information leading to a better assessment of multi-scale global and regional climate-related risks.
The latest developments and progress in climate forecasting on subseasonal-to-decadal timescales will be discussed and evaluated in this session. This will include presentations and discussions of predictions for a time horizon of up to ten years from dynamical ensemble and statistical/empirical forecast systems, as well as the aspects required for their application: forecast quality assessment, multi-model combination, bias adjustment, downscaling, etc.
Following the new WCPR strategic plan for 2019-2029, prediction enhancements are solicited from contributions embracing climate forecasting from an Earth system science perspective. This includes the study of coupled processes, impacts of coupling and feedbacks, and analysis/verification of the coupled atmosphere-ocean, atmosphere-land, atmosphere-hydrology, atmosphere-chemistry & aerosols, atmosphere-ice, ocean-hydrology, ocean-ice, ocean-chemistry and climate-biosphere (including human component). Contributions are also sought on initialization methods that optimally use observations from different Earth system components, on assessing and mitigating the impacts of model errors on skill, and on ensemble methods.
We also encourage contributions on the use of climate predictions for climate impact assessment, demonstrations of end-user value for climate risk applications and climate-change adaptation and the development of early warning systems.

A special focus will be put on the use of operational climate predictions (C3S, NMME, S2S), results from the CMIP5-CMIP6 decadal prediction experiments, and climate-prediction research and application projects (e.g. EUCP, APPLICATE, PREFACE, MIKLIP, MEDSCOPE, SECLI-FIRM, S2S4E).

Solicited talk:
Multi-year prediction of ENSO
By Jing-Jia Luo from the Institute for Climate and Application Research (ICAR), Nanjing University of Science Information and Technology, China

From interannual to multidecadal time scales, there is strong climate variability over both the tropical and extratropical regions of the globe. Several modes of both extratropical atmospheric circulation (NAM/AO, NPO, PNA, NAO, SAM/AAO, etc.) and sea surface temperature (AMO, PDO, North Pacific Gyre Oscillation (NPGO), North Atlantic tripole (NAT), etc.) have been proposed to explain the extratropical climate variability. These modes have profound impacts on the global and regional climates (i.e., temperature, precipitation, frequency of high-impact weather/climate events such as hurricane/typhoon, drought/flood and cold/heat waves, etc.). The associated dynamics and physical processes, such as the ocean-atmosphere interaction, coupled oceanic-atmospheric bridge, atmospheric internal dynamics and oceanic dynamics, are important for understanding the tropical-extratropical climate variability and thus have implications for the interannual to decadal predictability. However, the relevant dynamics and processes are not very well represented in current climate system models. Often this is due to a lack of observations of the processes being modelled. Contributions are welcome from, but not limited to, research on observational, theoretical and modeling studies on the following topics:
1. Physical processes and dynamics in the atmosphere/ocean and atmosphere-ocean coupling associated with the tropical-extratropical climate variability on time scales from years to multi-decades.
2. The impacts and teleconnections of the tropical-extratropical climate variability on a broad range of time scales and underlying physical mechanisms.
3. Comparison of observed and simulated tropical-extratropical climate variability and its climate impacts.
4. Predictability, prediction and projection of tropical-extratropical atmospheric and oceanic variability at various time scales.

In spring and summer 2018, Central and Northern Europe faced a severe drought with rainfall deficits beginning as early as April and lasting until late August in some regions (partly combined with a heat wave in July and August). Due to higher spring temperatures and high radiation the Baltic Sea showed a very unusal low pCO2 signal since late April and a spectacular summer bloom this year. The impact on terrestrial ecosystems became obvious through crop failure and forest fires. This transdiciplinary session calls for scientific results from Earth Observation showing the impact of the drought and for presentations from the interface between science a climate action e.g. adaptation strategies, questions on measuring, reporting and verification of inventories or general communication of climate change to societies.

Tipping elements in the Earth's climate system are continental-scale subsystems that are characterized by a threshold behavior. It has been suggested that these include biosphere components (e.g. the Amazon rainforest and coral reefs), cryosphere components (e.g. the Greenland and Antarctic ice sheets) and large-scale atmospheric and oceanic circulations (e.g. the thermohaline circulation, ENSO and Indian summer monsoon). Once operating near a threshold or tipping point, these components can transgress into a qualitatively different state by small external perturbations. The large-scale environmental consequences could impact the livelihoods of millions of people.

In this session, we aim to bring together experts presenting and discussing the state-of-the-art research on tipping elements in the Earth's climate system, both in empirical data and numerical modelling of past, present and future climate. Among other topics, issues to be addressed in this session include critical thresholds for specific tipping elements, typical time scales of tipping, interactions and feedbacks between tipping elements, the potential for tipping cascades as well as environmental and socio-economic impacts of tipping.