Causes and impacts of Greenland atmospheric Blocking changes

Recent research shows a significant increase in blocking over the Greenland region, mainly in summer, since around 1990. This is not well simulated by currently available global climate models. This deficiency may be linked to recent rapid Arctic sea-ice loss which is also not well captured by the climate models. However, the latest generation of climate models show some improvement compared with earlier versions, although still have some differences between modelled and observed representations of Greenland Blocking. Our proposal addresses this model-observation mismatch by means of a comprehensive comparison using new methods, the updated observations and the latest state-of-the-art climate model simulations. We seek to understand the causes of changes in Greenland Blocking through observation-based data on a wide range of timescales from daily to decadal, analysing how changes in extreme Greenland Blocking events are linked to climatological variations and trends, and considering fundamental physical causes (heating and/or atmospheric circulation changes) of extreme Greenland Blocking events. Natural variability is an important aspect of blocking, and the recent significant trend in Greenland Blocking in summer is the time of year when changes in Atlantic-wide sea-surface temperatures – called Atlantic Multidecadal Variability – are most closely associated with melt and runoff changes from the Greenland Ice Sheet. We will therefore compare climate-model output from models with varying representations of the ocean and sea ice in order to identify possible oceanic and/or Arctic sea-ice loss influences on Greenland Blocking changes. There would be profound implications of a continued increase in Greenland Blocking in summer over the coming decades: for example, enhancing melting and mass loss of the Greenland Ice Sheet. Recent results indicate a non-linear, accelerating response of the ice sheet’s surface melt and runoff to rising temperatures where the latter are partly linked with the recent blocking increase in summer. Crucially, understanding how the Greenland Ice Sheet responds to future climate change, and the resulting effects on global sea-level rise, depends upon being able to better model atmospheric circulation changes over the Greenland region. Therefore, we will use our insights gained from earlier work in the project and novel climate model experiments to evaluate the likely impacts of future Greenland Blocking changes on North Atlantic and European weather and climate, and on the Greenland Ice Sheet mass balance and hence global sea-level rise. We expect that our results from this climatically crucial part of the North Atlantic will provide a major step forward for understanding the causes and impacts of Greenland Blocking and help guide development of the next generation of global climate models.