Biomass Burning Emissions of Black Carbon over the Maritime Continent and ENSO Variability

Fire emissions from the Maritime Continent (MC) over the western tropical Pacific are strongly influenced by El Nino-Southern Oscillation (ENSO), posing various climate effects to the Earth system. In this study, we show that the historical biomass burning emissions of black carbon (BCbb) aerosol in the dry season from the MC are strengthened in El Nino years due to the dry conditions. The eastern Pacific type of El Nino exerts a stronger modulation in BCbb emissions over the MC region than the central Pacific type of El Nino. Based on simulations using the fully coupled Community Earth System Model (CESM), the impacts of increased BCbb emissions on ENSO variability and frequency are also investigated in this study. With BCbb emissions from the MC scaled up by a factor of 10, which enables the identification of climate response from the internal variability, the increased BCbb heats the local atmosphere and changes land-sea thermal contrast, which suppresses the westward transport of the eastern Pacific surface water. It leads to an increase in sea surface temperature in the eastern tropical Pacific, which further enhances ENSO variability and increases the frequency of ex-treme El Nino and La Nina events. This study highlights the potential role of BCbb emissions on extreme ENSO frequency, and this role may be increasingly important in the warming future with higher wildfire risks.