Paleoclimate data assimilation is reviewed with respect to convergence between proxy reconstructions and model ensembles of large-scale climate modes and circulation for the Holocene and last millennium. The chapter reviews progress in interpreting climate mode behaviour and teleconnection stationarity, particularly the North Atlantic Oscillation, the El Niño–Southern Oscillation (ENSO), the Southern Annular Mode, Zonal Wave 3, and sea ice indices. It presents approaches to resolving future problem climates using weather regime knowledge and causal networks of physical systems as applications of synoptic paleoclimatology. These include the realisation of past and future regional precipitation and winds with problem warm climates associated with tropical expansion or amplification (zonal mean Hadley Cell response) and ENSO (bias and amplitude); mid-latitude storm tracks, westerly winds, and precipitation dipoles; and polar amplification, amplified planetary waves, and extreme mid-latitude weather. Examples of causal networks and internal variability analogues that incorporate paleoweather and climate memory are applied to project future marine heat waves and cold spells.