Projecting Global Mercury Emissions and Deposition Under the Shared
Socioeconomic Pathways
Abstract
Mercury (Hg) is a naturally occurring element that has been greatly
enriched in the environment by activities like mining and fossil fuel
combustion. Despite commonalities in some CO2 and Hg emission sources,
the implications of long-range climate scenarios for anthropogenic Hg
emissions have yet to be explored. Here, we present comprehensive
projections of anthropogenic Hg emissions (2020-2300) and evaluate
impacts on global atmospheric Hg deposition. Projections are based on
four shared socioeconomic pathway (SSP) narratives ranging from
sustainable reductions in resource and energy intensity to rapid
economic growth driven by abundant fossil fuel exploitation. There is a
greater than two-fold difference in cumulative anthropogenic Hg
emissions between the lower-bound (110 Gg) and upper-bound (230 Gg)
scenarios. Hg releases to land and water are approximately six times
those of direct emissions to air (600-1470 Gg). At their peak,
anthropogenic Hg emissions reach 2200-2600 Mg a-1 sometime between 2010
(baseline) and 2030, depending on the SSP scenario. Coal combustion is
the largest determinant of differences in Hg emissions among scenarios.
Decoupling of Hg and CO2 emissions sources occurs under low- to
mid-range scenarios, though contributions from artisanal and small-scale
gold mining remain uncertain. A projected future shift in speciation of
Hg emissions toward lower gaseous elemental Hg (Hg0) and higher divalent
Hg (HgII) will result in a higher fraction of locally-sourced Hg
deposition. Projected re-emissions of previously deposited anthropogenic
Hg follow a similar temporal trajectory to primary emissions, amplifying
benefits of primary Hg emissions reductions under the most stringent
mitigation scenarios.