Dynamical vs. thermodynamical contributions to climate change: an analysis of idealized nudged model simulations

The daily to multi-decadal natural variability of large-scale atmospheric circulation makes it challenging to distinguish forced long-term trends and their impact on surface air temperature and precipitation changes. This study disentangles the thermodynamical and circulation-induced, i.e. dynamical, contributions to climate change using idealized model simulations having their large-scale free-troposphere circulation nudged towards either preindustrial or +4°C warmer world winds as previously simulated by the same model without nudging. In both seasons, thermodynamical changes are the primary contributor to the total climate change signals of surface air temperature and precipitation, yet changes in horizontal advection significantly reduce or raise the regional signal. Changes in vertical motion additionally impact precipitation changes, and it was found to be regionally dependent whether changes in horizontal advection or vertical motion are the dominant reason for the observed precipitation change. Quantifying the impact of changes in atmospheric circulation with climate change is therefore a necessity for regional climate change projections.