Effects of rapid Arctic climate change on jet streams and extreme weather (Ref 4606)

The lower atmospheric warming as a result of manmade CO2 emissions is several times larger in the Arctic than in other parts of the world, a phenomenon known as Arctic Amplification. The importance of this amplified warming could extend well beyond the Arctic, however. The midlatitude jet streams are effectively powered by the temperature difference between the warmer low latitudes and the colder high latitudes. Arctic amplification decreases this temperature gradient in the lowermost atmosphere, potentially impacting the jet stream and storms. Such changes could lead to an increase in extreme weather, which is a particular concern for the lives and livelihoods of the billions of people who live under the path of the jet stream. Arctic amplification is a robust phenomenon that appears clearly in state-of-the art climate models, and is relatively well understood. However, the response of the jet stream to Arctic amplification is far more uncertain, and varies substantially between different climate model experiments. By understanding what causes models to differ, we seek to reduce uncertainty in future projections of midlatitude climate and extreme weather. We will conduct experiments using a new, relatively simple but highly configurable global climate model known as Isca, developed by Dr Thomson and others at Exeter. Isca has the ability, unlike most climate models, to be able to turn relevant processes on and off, and to 'nudge' the atmosphere to different background states. By using these features, we can investigate how jet stream responds to Arctic amplification in a controlled manner, and ascertain which processes are the most important. We will combine data from sophisticated climate models run as part of the Polar Amplification Model Intercomparison Project and results from Isca to understand better how biases in present day climate can influence predictions of jet stream properties, and the impacts on extreme weather.