The radiative forcing from aerosols (particularly through their interaction with clouds) remains one of the most
uncertain components of the human forcing of the climate. Observation-based studies have typically found a smaller aerosol
effective radiative forcing than in model simulations and were given preferential weighting in the IPCC AR5 report. With their
own sources of uncertainty, it is not clear that observation-based estimates are more reliable. Understanding the source of the
model-observational difference is thus vital to reduce uncertainty in the impact of aerosols on the climate.
These reported discrepancies arise from the different methods of separating the components of aerosol forcing used in model
and observational studies. Applying the observational decomposition to global climate model output, the two different lines
of evidence are surprisingly similar, with a much better agreement on the magnitude of aerosol impacts on cloud properties.
Cloud adjustments remain a significant source of uncertainty, particularly for ice clouds. However, they are consistent with
the uncertainty from observation-based methods, with the liquid water path adjustment usually enhancing the Twomey effect
by less than 50%. Depending on different sets of assumptions, this work suggests that model and observation-based estimates
could be more equally weighted in future synthesis studies.