Processes controlling the South American Monsoon response to Climate Change

CMIP6 future climate projections consistently show a drying trend during the onset of the South American monsoon, which has the potential for large ecological and societal impacts in this region. This trend is also present in a high-resolution regional convection-permitting simulation over the South American domain. Here, the processes responsible for this drying trend are examined using a number of idealised experiments and analysis techniques. The main driver is shown to be remote sea surface temperature (SST) warming - rather than local radiative or plant physiological responses to increased CO₂ - with both large-scale uniform SST warming and patterned regional warming playing important roles. The role of uniform SST warming on the South American monsoon onset is examined in more detail using a moist static energy budget approach, building on hypotheses from a previous single model study. The atmospheric circulation response to patterned SST warming is examined using a local overturning circulation partioning technique, allowing a link between the South American monsoon region and specific regions of ocean warming to be identified.