In this short Stefan Rahmstorf talks about the devastating heat waves that will characterise the climate of 2100 if the global mean temperature becomes 4°C warmer than preindustrial temperatures.

Temperature anomalies that are associated with highly unusual heat extremes today (namely, 3-sigma events occurring only once in several hundreds of years in a stationary climate) will have become the norm over most (greater than 50 percent) continental areas by the end of the 21st century. Five-sigma events, which are now essentially absent, will become common, especially in the tropics and in the Northern Hemisphere (NH) mid-latitudes during summertime.

Outside the tropics, the NH subtropics and mid-latitudes are expected to experience much more intense heat extremes during the boreal summer. In the Mediterranean, North Africa, the Middle East, the Tibetan plateau, and the contiguous United States, almost all (80 percent to 100 percent) summer months will be warmer than 3-sigma and approximately half (about 50 percent) will be warmer than 5-sigma. This implies that temperatures of the warmest July within the period 2080–2100 in the Mediterranean region, for example, are expected to approach 35°C, which is about 9°C warmer than the warmest July estimated for the present day.

This short is based on a report that PIK (the Potsdam Institute for Climate Impact Research) did for the World Bank.
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.

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