Coastal impacts of sea -level change can result from individual extreme sea -level and wave events, or long -term fl uctuations in mean sea level, or most likely from a combination of processes. An example of a combined impact is the damage caused by Hurricane Katrina at New Orleans, which resulted in unprecedented storm -surge levels and failure of coastal defenses. This was compounded by the rate of local mean sea -level rise relative to the land level of the Mississippi Delta of several times the global average, as occurs naturally in all major deltas, together with anthropogenic changes to the delta wetlands. On much longer timescales, extremes and mean -sea -level change are both major factors in determining coastal evolution including the development of coastal ecosystems.It will be seen below that, although it is diffi cult to determine how mean sea level has changed in the past and will change in the future and to determine the reasons for change (the main topics of this volume), the very nature of extreme events makes estimation of future extreme levels a more diffi cult task. However, for many practical purposes, the study of extremes is far more important than that of mean sea level alone. Extremes often result in loss of life and great damage to infrastructure and the environment, and knowledge of their historical, and potential future, amplitudes and frequencies determines the scale of resources required for adaptation and coastal protection (see Figure 11.1 ).This chapter discusses changes in extreme sea levels and waves and is divided into four parts. First, we review changes in extreme sea levels and waves in the recent past. Then we discuss changes in the atmospheric storm events that drive extreme sea -level changes. There follows a review of recent advances in the modeling of future extreme events. (The reader is referred to the list of abbreviations and acronyms at the front of the book for models mentioned in the text.) The European shelf, Bay of Bengal and Australian regions have been investigated in greater detail than most other areas, and are selected for this section as special case studies of future change. Finally, we highlight issues that we believe need to be addressed in order to further understand the changes of the past and better predict those of the future.

The paper describes the initial efforts in a project whose objective is to obtain a 40-year hindcast of wind, sea level and wave climatology for European waters. The 40-year global atmospheric re-analysis carried out by the National Centre for Environmental Prediction, Washington, USA (NCEP) and the National Centre for Atmospheric Research, Boulder, Colorado, USA (NCAR) will be used as forcing of limited area atmospheric models. The fine grid atmospheric fields will be used to force state-of-the-art wave models (WAM) and sea level models (HAMSOM and TELEMAC) in regional areas around Europe so as to produce climatic information on waves, sea levels, and currents in a very large extend of the European waters, including the Mediterranean, North East Atlantic and North Sea. The available satellite data, including wind, wave and sea-level data, will be collected and will be used to be compared with the hindcast results, so as to yield uncertainty measures related to the data. Statistical analysis of the produced atmospheric, sea level and wave hindcast and remote sensed data will be performed in order to provide information about the climatological trends in the European Waters and Coastal Seas.

Abstract. Based on the Baltic Earth Assessment Reports of this thematic issue in Earth System Dynamics and recent peer-reviewed literature, current knowledge about the effects of global warming on past and future changes in climate of the Baltic Sea region is summarized and assessed. The study is an update of the Second Assessment of Climate Change (BACC II) published in 2015 and focusses on the atmosphere, land, cryosphere, ocean, sediments and the terrestrial and marine biosphere. Based on the summaries of the recent knowledge gained in paleo-, historical and future regional climate research, we find that the main conclusions from earlier assessments remain still valid. However, new long-term, homogenous observational records, e.g. for Scandinavian glacier inventories, sea-level driven saltwater inflows, so-called Major Baltic Inflows, and phytoplankton species distribution and new scenario simulations with improved models, e.g. for glaciers, lake ice and marine food web, have become available. In many cases, uncertainties can now be better estimated than before, because more models can be included in the ensembles, especially for the Baltic Sea. With the help of coupled models, feedbacks between several components of the Earth System have been studied and multiple driver studies were performed, e.g. projections of the food web that include fisheries, eutrophication and climate change. New data sets and projections have led to a revised understanding of changes in some variables such as salinity. Furthermore, it has become evident that natural variability, in particular for the ocean on multidecadal time scales, is greater than previously estimated, challenging our ability to detect observed and projected changes in climate. In this context, the first paleoclimate simulations regionalized for the Baltic Sea region are instructive. Hence, estimated uncertainties for the projections of many variables increased. In addition to the well-known influence of the North Atlantic Oscillation, it was found that also other low-frequency modes of internal variability, such as the Atlantic Multidecadal Variability, have profound effects on the climate of the Baltic Sea region. Challenges were also identified, such as the systematic discrepancy between future cloudiness trends in global and regional models and the difficulty of confidently attributing large observed changes in marine ecosystems to climate change. Finally, we compare our results with other coastal sea assessments, such as the North Sea Region Climate Change Assessment (NOSCCA) and find that the effects of climate change on the Baltic Sea differ from those on the North Sea, since Baltic Sea oceanography and ecosystems are very different from other coastal seas such as the North Sea. While the North Sea dynamics is dominated by tides, the Baltic Sea is characterized by brackish water, a perennial vertical stratification in the southern sub-basins and a seasonal sea ice cover in the northern sub-basins.

This chapter contains sections titled: * Sea State * Tides * Acknowledgment * Reference