Motivation:

The role of decadal variability in climate has been a subject for investigations since the advent of modern climate research and a title for many past meetings and workshops. That said, several recent developments make the holding of another workshop on the subject timely:

• Recent years saw the proliferation of new instrumental observations, particularly in the ocean and from space. These lead to advancements in coupled model-based climate prediction, including initialized decadal prediction. The international effort under CMIP5 in this area provided material for an initial but incomplete assessment of the benefit and use of such predictions.
• Reconstructions of past, pre-instrumental climate variability from high-resolution single and multiple proxy datasets advanced and provided new information on decadal variability during the pre-industrial era.
• The proxy-based reconstructions also served as validation for a concerted CMIP5 effort on coupled model simulate of last millennium climate variability. In particular these simulations were conceived to assess the response of surface temperature and precipitation to solar variability, volcanic forcing, and changes in land use and to contrast this response with the response to anthropogenic greenhouse gas emission and industrial aerosols. The analysis of these experiments has provided useful understanding of the response to external natural forcing but also revealed perplexing model inconsistencies that require further analysis and study.

Despite all the advances in observational analysis and modeling, the research community was caught by surprise by the slowdown in the rate of global surface temperature change since the late 1990’s. Climate researchers were quick to propose and test various hypotheses for this “warming hiatus” but the verdict is still out as to its cause and to the failure of initialized coupled model predictions to detect it. Faced with these developments, the WCRP and its core projects, particularly CLIVAR identified the need to advance the study of decadal climate variability and predictability (DCVP) and to continue experimental climate prediction under WGCM and WGSIP. Given these considerations, a workshop on DCVP to discuss the progress, identify the remaining challenges and lay out the way to address them is timely