Attribution of multi-annual to decadal changes in the climate system

Understanding the drivers of multi-annual to decadal changes in the climate system is essential for building confidence in forecasts, for quantifying hazards, and for developing robust adaptation and mitigation policies. However, our capability in this regard is very immature, as highlighted by the recent debate around the temporary slowdown in global surface warming in the early 21^st century. Hence, the WCRP Lighthouse Activity on Explaining and Predicting Earth System Change is being developed to address this need.

The aim of this workshop on “Attribution of multi-annual to decadal changes in the climate system” is to document current research, identify challenges, and explore potential pathways towards building an operational capability to attribute multi-annual to decadal changes in the climate system on global-to-regional scales.

Key areas to be addressed include:

• To what extent is the observing system adequate for the task and how best to use the observations
• Approaches to assess the roles of internal variability and external factors including greenhouse gases, aerosols, solar variations, volcanic eruptions, ozone and land use.
• To what extent are models adequate for the task and how to account for model errors, including underestimated signals
• To what extent do responses to different forcings add linearly
• How to account for forcing uncertainties?
• Analysis of physical processes
• Linking large scale circulation to regional weather and climate hazards
• Steps needed to build an operational capability