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Dynamical controls on regional aspects of climate change

Final Report Summary - DCRACC (Dynamical controls on regional aspects of climate change)

The main purpose of the CIG is to facilitate the rapid integration of the researcher within their new country. By this measure the project has been an unqualified success. Following his move from Canada in 2012, Professor Shepherd quickly established himself at the University of Reading, building up a large and high-quality research group in the area of atmospheric circulation and its role in regional aspects of climate change, and developing collaborations within the UK and more widely across Europe. He plays a significant leadership role within the University of Reading as the Research Division Leader for Climate, and within the UK as Chair of the Science Review Group of the Met Office Hadley Centre. He has organized three inter-disciplinary scientific meetings under the auspices of the Royal Society, and has given numerous seminars and invited talks at scientific meetings on atmospheric circulation as a source of uncertainty in climate change, as well as publishing an invited Perspective in Nature Geoscience on the topic. In 2013 Professor Shepherd won an Advanced Grant from the European Research Council, which was very much an elaboration of the research program outlined for this CIG project, but fleshed out and scaled up to a large research effort.

Professor Shepherd’s contact information and research group description can be found at www.met.reading.ac.uk/userpages/sj903980.php

The CIG project itself had three main objectives: (i) improving models, (ii) making better use of existing model projections, and (iii) estimating climate variability and extremes.

Objective (i) was addressed by bespoke model sensitivity studies, with a focus on parameterized drag processes relevant to the atmospheric momentum budget. This is a comparatively unexplored aspect of climate modelling, compared to convection and clouds. The results on orographic drag have been particularly significant, showing that (a) it is a major factor in errors in storm-track tilt over the North Atlantic, a long-standing model error with direct implications for European climate; (b) it is directly linked to uncertainty in the storm-track response to climate change; and (c) similar errors are manifest in weather prediction. The results of this research are being used by the European Centre for Medium-Range Weather Forecasts and the UK Met Office to improve their models.

Objective (ii) was addressed by the innovative use of the CMIP5 multi-model ensemble, disentangling true differences between models and internal variability so as to make better use of the information contained in such multi-model ensembles, and identifying the role of atmospheric circulation in crucial climate impacts such as Mediterranean drying. As a practical way of representing uncertainty in the circulation response to climate change, the project developed a novel ‘storyline’ approach. This provides an alternative to more statistical approaches that is more physically self-consistent and thus better tailored to assessing compound risks. The results are being used by the UK Met Office to understand and communicate climate projections being developed for government policy needs.

Objective (iii) was addressed by (a) examining the physical processes and mechanisms behind atmospheric variability, and (b) developing novel approaches to assessing risks associated with weather and climate extreme events. Under (a), the project showed that summertime climate variability in the Southern Hemisphere midlatitudes is most effectively understood as variability in the seasonal transition of climatic regime, rather than the more usual interpretation of anomaly about a seasonal climatic average. The results form the basis of a proposal to the Royal Society on Southern African summertime seasonal prediction, with South African partners and stakeholders. Under (b), the project has applied the ‘storyline’ approach developed in (ii) to the problem of extreme event attribution. The results will be used in a recently-funded UK NERC research project with Oxford, and will form the basis of the researcher’s contribution to a consortium proposal currently being developed for H2020 FET, with industrial stakeholders.