Changing Atmospheric Blocking

Atmospheric blocking has long been considered one of the key weaknesses of numerical weather and climate models. Many climate scientists are concerned that models are not able to accurately simulate blocking events, and yet if there were to be a change in blocking behaviour this would have a large impact on regional climate. Persistent blocking anticyclones lead to extreme heatwaves and drought in summer and extended cold spells in winter. Such events have been instrumental in leading to several recent extreme seasons in Europe. This project will provide a comprehensive assessment of how well blocking is simulated in state of the art climate models. We will evaluate the ability of the models to reproduce the occurrence of blocking that we see in observations, and we will also for the first time provide a diagnosis of which timescales are responsible for any model biases that we find. Based on the projections of the different climate models we will produce an assessment of how blocking may change in response to future greenhouse gas forcing, and how much confidence we should have in these projections. For Europe, conclusions will be drawn for the likely future occurrence of extreme heatwaves and drought in summer and cold spells in winter.