The North Atlantic jet stream has become dramatically more variable from one winter to the next over the past few decades, and no one yet knows why. This matters because the jet stream drives the UK’s winter weather. When it shifts, the country gets hit harder by storms, floods, cold snaps, or dry spells. Current climate models can reproduce some of this variability, but they cannot explain the recent surge in year-to-year swings, leaving huge uncertainty in regional climate predictions for the coming decades. The researchers will test whether factors such as sea-ice loss, ocean heat exchange, or volcanic eruptions are combining to make the jet stream more erratic. They will run the latest global climate models through machine-learning tools to identify which drivers matter most, then use those relationships to constrain projections of jet-stream behaviour out to 2100. If successful, the work will give energy operators, transport planners, and insurers a clearer picture of how winter extremes may change. It will also improve seasonal-to-decadal forecasts, helping infrastructure managers prepare for what is coming rather than reacting after the fact.
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The North Atlantic atmospheric polar jet stream (giant current of air) has a major influence on climatic conditions and extreme weather fluctuations across the UK and Northwest Europe. A number of factors can cause the jet stream to vary, including changes in snow cover and sea ice, exchanges of energy between the sea and air, changes in energy from the Sun, volcanic eruptions, and conditions in the middle layer of the atmosphere. Crucially, the most recent few decades have seen a major increase in how much the jet stream varies between successive winters. This suggests that certain factors that drive the jet stream might have become more active and/or acted more in concert during this recent period. Changes in jet-stream variations directly affect the strength and frequency of extreme weather (e.g. temperature, rain-/snow-fall and wind-storm events) across the UK and neighbouring parts of Europe, which then have consequences for the operation of key/critical infrastructure sectors such as energy and transport, or generate significant insurance losses. Therefore, improving understanding of jet-stream drivers is vital for improving prediction of future regional climate change, about which there is substantial current uncertainty. Global climate models (supercomputer representations of the physical climate system) already show reasonable potential to represent North Atlantic jet-stream variations during the winter season. However, to gain a step change in the understanding of the capabilities and limitations of such models at the regional level and to improve regional climate prediction, more comprehensive evaluations are needed. We therefore propose a novel evaluation of North Atlantic jet-stream changes in large numbers of state-of-the-science global climate model simulations that have recently been produced by a couple of other key inter/national projects, using the latest observation-based climate datasets as a benchmark. In addition to analysing new global climate model output, we would also use innovative machine learning tools to evaluate the relationship between a set of hypothesised climatic precursor conditions, called (potential) jet-stream drivers, and jet-stream variability. We would then develop a set of constraints, based on relations between global climate model representation of the observed jet stream and model-projected future climate change, with the goal of developing unique and robust predictions of changes in North Atlantic jet-stream variability to the year 2100. We would also provide critical guidance for end-users and stakeholders to help prepare for climate-related impacts of likely future variations in the jet stream. Our proposed approach would allow us to test key hypotheses of possible causes of trends and extremes in the jet stream and could provide valuable insights for seasonal-to-decadal climate prediction. The proposed work, which is the first time the observed year-to-year changes in jet stream variance have been tackled, is not only important from theoretical and end-user perspectives but is also highly timely with the availability of new large sets of models. The proposal’s Objectives are to: (O1) Ascertain to what extent global climate models capture the observed changes and extremes in North Atlantic atmospheric jet-stream variability, especially the observed increase in winter variability and accompanying UK weather extremes since ~2000; (O2) Understand the causes of the observed changes in jet-stream variability (externally-forced change from various jet-stream drivers versus random fluctuations); (O3) Assess and constrain future changes in jet-stream variability out to 2100, and the accompanying impacts of UK and Northwest Europe weather extremes on relevant stakeholders.
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