Aerosol effects on clouds operate at spatial scales of short-lived cloud updrafts (typically 100 m - 100 km), yet exert a global effect on climate over multiple decades. The multiscale nature of these indirect effects on the planetary energy balance presents particular challenges to climate modeling, which has led to large uncertainties in estimates of indirect effects. The most difficult types of aerosol indirect effects to quantify are those for which the aerosol sources are controlled by complex interactions of ecosystems with climate, such as the aerosol emissions from ocean phytoplankton and from wildfires in forests. This project addresses these challenges through a combination of advanced parameterizations, explicit modeling, and observations with a multi-institutional, multi-disciplinary team of experts. The treatment of turbulence in a multiscale model of cloud-aerosol interactions is being improved, the cloud-aerosol interactions simulated by the multiscale model are being evaluated, and the model is being merged into and released to the public as an option in the Community Atmosphere Model (CAM). Advanced parameterizations of aerosol effects on stratocumulus, shallow cumulus, and deep cumulus clouds in CAM are being brought together into a common framework for multi-decadal simulations with coupling with the ocean. These simulations with and without aerosol feedbacks are being examined to determine the influence of aerosol indirect effects on decadal climate variability. This evaluation will be accomplished by relating climate-scale changes in oceanic and atmospheric conditions over the Pacific to the sensitivities of regional ocean-atmosphere interactions to aerosols along the west coast of North America and consequent atmospheric conditions over the entire United States.