Mercury Emissions under Different Climate Pathways

Global anthropogenic mercury (Hg) emissions are a long-lived hazard to human and environmental health. Targeted efforts to ban anthropogenic uses and trade and other releases of mercury and its compounds are underway through the UN Minamata Convention on Mercury [1]. However, more than half of Hg emissions in 2015 were linked to unintentional release via the combustion of fossil fuels (especially coal) and industrial activities such as metals production. Thus, in addition to mercury-specific policies and interventions, global action on climate change and the accompanying transition in energy systems, as well as the demand for metals and cement are important drivers of future mercury emissions.

The Greenhouse Gas – Air Pollution Interactions and Synergies (GAINS) model is an integrated assessment model that explores cost-effective multi-pollutant emission control strategies which aim at maximizing impacts of improved local and global air quality and emissions abatement. Hg-GAINS, as developed by Rafaj et al. [2] is one of few models which currently represents all anthropogenic mercury emission sources on a sector-by-sector basis. A recent update enhances representation of the co-benefits for mercury emissions from particulate matter (PM) and SO₂ controls and extended the representation of Hg-specific control technologies. Climate and energy policy is represented through exogenous inputs into the model.

We quantify the relative importance of climate policy, co-benefits from PM and SO₂ controls and technological mercury pollution control measures by comparing six scenarios of global mercury emissions in 5-year steps from 2010 up to 2050. Three energy scenarios from IEA World Energy Outlook 2022 (A - “Stated Policies (STEPS)”,  B - “Advanced Pledges (AP)”,  C - “Net Zero Emissions (NZE)”  [3]) are combined with two strategies of mercury emission control (1 - Current Legislation (CLE) , assuming technical mercury control compliant with the Minamata convention and national emission standards, relying mainly on co-benefits from PM and SO2 control; 2 - Maximum Feasible Reduction (MFR), assuming utilisation of the most efficient Hg-specific technologies and measures across all sectors). The share of Hg emissions from fossil fuel combustion is decreasing significantly in the Net Zero scenario (NZE-CLE) by 2050. Additionally, stringent air pollution policy reduces Hg emissions from this sector globally in all energy CLE scenarios. However, material and metal demand, driven by the deployment of renewable energy, as well as population growth both lead to a net increase of Hg even in NZE-CLE, which can only be resolved by applying stringent MFR controls for mercury (NZE-MFR).

[1] UNEP (2019). Minamata Convention on Mercury. Text and Annexes. www.mercuryconvention.org.

[2] Rafaj, P., Bertok, I., Cofala, J., and Schöpp, W. (2013). Scenarios of global mercury emissions from anthropogenic sources. Atmospheric Environment, 79:472–479.

[3] International Energy Agency (2022). World Energy Outlook 2022.