Aerosol-cloud interactions make up a strong but highly uncertain aspect of the projected climate response to future warming. Anthropogenic aerosols contribute a negative radiative forcing by changing the albedo and macrophysical properties of clouds, but the magnitude of this effect is not well constrained in current earth system models. Many of the physical processes driving aerosol-cloud interactions occur at subgrid scales and must be parameterized, which introduces uncertainty into model simulations. Perturbed parameter ensembles (PPEs) can address this parametric uncertainty by exploring the effects of varying multiple parameters across a range of possible values at the same time. As part of PROCEED (PPE Regression Optimization Center for ESM Evaluation and Development), we build a PPE using version 3 of the DOE Energy Exascale Earth System Model (E3SM) under an atmosphere-only configuration. Compared to previous versions of the model, E3SMv3 has improved representations of microphysics and aerosols which make it ideally suited to study this problem. In the E3SMv3 PPE, we perturb 15 parameters related to aerosols, convective microphysics, accretion, and autoconversion in an ensemble of 100 simulations of both pre-industrial and present-day aerosol forcings. We examine the parametric uncertainty in E3SMv3 and the aerosol-cloud interactions in warm liquid clouds in the PPE. We also constrain the PPE results with ground-based observations from the DOE Atmospheric Radiation Measurement (ARM) site in the Eastern North Atlantic. The E3SMv3 PPE, along with ARM observations, may help advance our understanding of the magnitude of radiative forcing due to aerosol-cloud interactions.