IPCC AR6 WGI Chapter 10: Linking global to regional climate change

A. A. Sörensson, F. J. Doblas-Reyes, M. Almazroui, A. Dosio, W. Gutowski, R. Haarsma, R. Hamdi, B. Hewitson, M. Jury, W.-T. Kwon, B. Lamptey, D. Maraun, T. Stephenson, I. Takayabu, L. Terray, A. Turner, Z. Zuo

 Abstract:  We assess the foundations of how regional climate information is distilled from multiple, sometimes contrasting, lines of evidence from observations and models that help link the global change to the region.  The distillation process includes recognizing the challenges and requirements associated with observations relevant at the regional scale and the fitness of modelling tools available for attributing and projecting anthropogenic climate change in a regional context.  Modeling tools yielding regional climate change include global and regional models and statistical downscaling.  Regional climate change may be caused by natural internal processes, such as unforced, internal variability on various space and time scales, and by external forcings such as solar cycles, volcanic eruptions and persistent anthropogenic changes in atmospheric composition or land use and land cover.  Multi-model ensembles can help delineate the interplay between anthropogenic and other external forcings and internal variability and also enable the assessment of regional climate response uncertainty.

Regional-scale detection and attribution studies as well as observed emergence analysis provide robust evidence supporting the dominant contribution of anthropogenic forcings to regional temperature changes over multidecadal periods.  For regional, multidecadal precipitation changes, attribution is more challenging though for some regions the contribution of anthropogenic forcing does emerge.

Although methodologies for distillation have been established, the distillation process is in practice conditioned by the sources available, the actors involved and the context, which depend heavily on the regions considered, and framed by the question being addressed.  To make the most appropriate decisions and responses to a changing climate, it is necessary to consider all physically plausible outcomes from multiple lines of evidence, especially in the case when they are contrasting.  Confidence in the distilled regional climate information is enhanced when there is agreement across multiple lines of evidence.  The resulting climate information can then be integrated, following a co-production process involving both the user and the producer, into a user context.