Impacts of socio‐economic development scenarios on long‐term oceanic emissions and abundances of atmospheric bromoform and dibromomethane

Abstract

Oceans are the primary source of atmospheric bromoform (CHBr3) and dibromomethane (CH2Br2), with implications for tropospheric chemistry and the ozone layer. Nevertheless, socio-economic developments are changing the oceans' biological characteristics, which could impact the magnitude and distribution of oceanic emissions in the future. In this work, we couple a machine learning (ML) framework to the Community Earth System Model (CESM) data of the Coupled Model Intercomparison Project (CMIP) and estimate the monthly sea surface concentrations of CHBr3 and CH2Br2 between 2015 and 2100, under different climate change scenarios. We use these estimates to run CESM version 2 (CESM2), with comprehensive halogen chemistry, and calculate present-day global emissions of 269–271 Gg Br and 61–65 Gg Br for CHBr3 and CH2Br2, respectively, based on different scenarios. Furthermore, we project 14%–40% and 8%–23% increases for global mean emissions of CHBr3 and CH2Br2, respectively, by 2100; where more stringent scenarios lead to smaller enhancements. Regionally, there are uncertainties within the magnitudes and signs of the changes that depend on the climate scenarios considered. Nevertheless, the largest enhancements, under all scenarios, were predicted over the western tropical Pacific Ocean, tropical Atlantic Ocean, and Indian Ocean. We attribute these changes primarily to biological parameters rather than physical parameters. These changes project a 0.47–1.13 ppt Br increase from the combined source gases (CHBr3 and CH2Br2) in the upper troposphere by 2100, which could impact the stratospheric ozone budget. Overall, this study highlights the far-reaching influence of human activities on natural oceanic emissions and atmospheric chemistry.