Combining different views on internal climate variability of temperature over Europe

Internal climate variability (ICV) is an important source of climate change projections uncertainty. The estimate of ICV can serve as a useful benchmark for assessing climate model performance and the emergence of anthropogenically forced climate change. Nevertheless, estimating the magnitude of ICV is challenging, especially on a regional scale. The ICV itself is state-dependent, which further complicates the assessment under transient climate change conditions. This study aims to quantify the magnitude of ICV using different types of data, i.e., earth system model simulations and observation-based datasets. We focus here on seasonal mean temperature over Europe and confront different methodological approaches: comparison of variability inferred from pre-industrial control simulations with the spread of single-model initial-condition large ensemble, separation of uncertainty sources in CMIP6 transient simulations, and forcing attribution in observed time series. In case of the large ensemble data, we also pay attention to the temporal development of ICV magnitude under changing external forcing.