Past and projected future changes of North Atlantic polar low frequency Matthias Zahn Polar lows are vigorous and fast developing storms threatening human offshore activities in polar waters. Due to their small spatial scale polar lows are underrepresented in most global reanalysis and climate model data. By means of dynamical down-scaling it has become possible to simulate polar lows with a Regional Climate Model (RCM) and track them in the output fields of long-term RCM simulations. To investigate their long-term frequency changes over the North Atlantic a RCM was driven with NCEP reanalysis data for the past as well as with global data of IPCC future projections and polar lows were counted in the output data. While there could no systematic change of polar low frequency be found in the past, a significant decrease in the number of annual cases was discovered associated with projected anthropogenic warming of the atmosphere. This decrease is linked to an increase in atmospheric stability with warming, which is a result of faster rising air temperatures compared to sea surface temperatures. The influence of changing large scale ocean currents on the atmospheric stability over the North Atlantic will also be discussed.