SEA LEVEL WORKSHOP From global to coastal, from past to future

Planet Earth is globally warming mostly due to human activities. More than 90% of this energy has warmed the global ocean. The remaining has served to warm the atmosphere, the land and to melt both the land ice (ice sheets and glaciers) and floating sea ice. Global mean sea level rise is one of the most direct consequences of the actual global warming. This global rise is caused by ocean warming (known as thermosteric sea level) and the imports of fresh water from continents (i.e., ice sheets mass loss, mountain glaciers melting and land water change). Satellite altimetry data have revolutionized our knowledge on sea level change because of the near global coverage. For the first time, it has been shown that the global mean sea level trend experiences large regional variability. In addition to ocean warming and land ice imports, regional sea level changes are also sensitive to salinity changes, ocean circulation, atmospheric pressure, wind stress and air sea heat fluxes. These large-scale regional sea level changes may interact with the land throughout the coastal areas. The coastal areas are exposed to a large range of coastal hazards. Mean sea level rise will lead to flooding of the low-elevation coastal zones. Tropical cyclones or extra-tropical storms generate storm surges, causing devastating coastal flooding. For example, in 1970, Bhola cyclone hit Bangladesh coasts, killing 300 000 people, whereas in 2004, Hurricane Katrina hit severely the U.S. Louisiane and Mississipi coasts, killing 1 200 people. At the same time, the coastal areas are more and more densely populated. The number of people living in the low-elevation coastal zones could double between 2000 and 2060. In this context, it is essential to understand the sea level changes, in order to protect our coasts in the future.