Aerosol and Cloud Interactions over South America During the Next Century

Aerosols are tiny solid or liquid particulates that become suspended in the atmosphere and come from both natural or anthropogenic sources. Not only can aerosols act as the cloud condensation nuclei (CCN) needed for droplet growth, but they also can reflect or absorb solar or longwave radiation, altering the radiative budget and climate of the planet. Aerosol-cloud interactions are one of the highest areas of uncertainty in current climate models, and therefore it is important to understand potential implications an increase or decrease in aerosols could have during a changing climate. To address this question, this study investigates aerosol-cloud interactions using an average of thirty-three ensemble members in the Community Earth System Model – Large Ensemble (CESM-LENS) dataset to investigate increased aerosol burden that could occur over the Amazon Rainforest by the 2070-2079 decade. This model uses a RCP8.5 climate scenario to project a possible future in which humans do not implement climate policy to reduce fossil fuel emissions. Seasonal and decadal averages were used between the 2010-2080 period to investigate an increase in aerosol absorption that the model suggests will occur in the mid-levels over the Amazon due to increased biomass burning. Results indicate that a 70% increase in aerosol absorption could be expected in the mid-levels of the troposphere over the forest by the 2070-2079 decade, along with a 30% increase in CCN concentrations. Additionally, tests confirm that an increase in aerosols from biomass burning would correlate to an increase in aerosol transport aloft over the equatorial Pacific Ocean. Resultantly, a possible 6% increase in mid-to-high-level cloud fraction could be expected over the Amazon and Pacific Ocean, and could cause a reduction in solar radiation able to reach the surface by 10 W/m2, on average, during summer for the 2070-2079 decade.