Sea-level rise is one of the inevitable results of global warming, as warmer ocean waters expand and land ice melts and adds water to the oceans. Observations show that the seas are indeed rising and that the rise in the 20th century is unique in the context of the previous millennia. However, more difficult to answer is the question of how fast and how far sea level will rise in the future. The billion-dollar-question is: How stable are the ice sheets on Greenland and Antarctica? Stefan Rahmstorf obtained his PhD in oceanography at Victoria University of Wellington in 1990. He has worked as a scientist at the New Zealand Oceanographic Institute, at the Institute of Marine Science in Kiel and since 1996 at the Potsdam Institute for Climate Impact Research. His work focuses on the role of the oceans in climate change. In 1999 Rahmstorf was awarded the $ 1 million Centennial Fellowship Award of the US-based James S. McDonnell foundation. Since 2000 he teaches Physics of the Oceans as a professor at Potsdam University. Rahmstorf served from 2004–2013 in the German Advisory Council on Global Change (WBGU) and was one of the lead authors of the 4th IPCC Assessment Report. Dr. Rahmstorf has published over 100 scientific papers (30 in leading journals such as Nature, Science and PNAS) and co-authored four books. Available in English are Our Threatened Oceans (2009, with Katherine Richardson) and The Climate Crisis (2010, with David Archer).