Figure 1:

Conceptual framework. Due to a challenging parameterization, chemical transport models (CTMs, GEOS-Chem in this study) traditionally hold legacy emissions constant at present-day (2010) levels when making future projections. The latter thus only reflect changes in direct anthropogenic emissions. Using a fully-coupled seven-reservoir global biogeochemical cycle model^11,16 we account for future legacy emissions as a result of both past and future emissions by adjusting GEOS-Chem outputs. The effective policy impacts in terms of local Hg deposition are then dependent on policy delay. The adjusted deposition flux is then used as input to a lake Hg model to evaluate the response of fish contamination to delayed action. Current Policy (CP), New Policy (NP) and Maximum Feasible Reduction (MFR) refer to future global emissions scenarios developed by Pacyna et al.⁹.