Disentangling anthropogenic forced dynamic and thermodynamic precipitation changes from internal variability over the past seven decades

The separation of human-induced climate change and internal unforced variability to precipitation changes is well established, yet the full extent of anthropogenic forcing in regulating terrestrial precipitation remains unclear. Here we present a novel approach that combines dynamical adjustment with fully coupled nudged circulation climate model simulations using the Community Earth System Model Version 2 (CESM2) to attribute anthropogenic contributions to forced thermodynamic and dynamic processes driving seasonal mean precipitation trends over the past seven decades, while isolating the influence of internal variability. We show that although anthropogenic forced thermodynamics increases terrestrial precipitation over the majority of land areas in boreal summer (~52.3% ) and winter (~78.3%), it dampens precipitation over hot and humid areas, likely because of terrestrial evaporation failing to balance the rising saturation deficit of a rapidly warming atmosphere. Opposing the traditional expectation of small human-induced changes in circulation patterns, we find that atmospheric circulation patterns shift in response to anthropogenic forcing and modulate mean precipitation with similar magnitudes as forced thermodynamics, in particular suppressing precipitation in humid regions. Our results not only reveal that the climate system responds to anthropogenic emissions with declining precipitation in some wet areas, but also demonstrate that these tendencies are influenced by both thermodynamic changes and shifting large-scale dynamic systems.