Climate change threatens to release legacy mercury reserves

Researchers from the Spanish National Research Council (CSIC) have warned in the journal Science that climate change threatens to re-release massive reserves of legacy mercury into the environment. While international efforts and industrial restrictions have successfully reduced new human-driven emissions in Europe, North America, and East Asia, much of the mercury currently in the atmosphere is not new.

Approximately 60% of atmospheric mercury is considered ‘legacy mercury’—pollutants emitted centuries ago through mining and coal combustion that continue to cycle between soil, water, and air. Because mercury does not degrade, it remains stored in ecosystems for long periods, only being permanently removed when buried in deep marine sediments over a thousand-year process.

Global warming is expected to mobilize these stored reserves through several mechanisms: forest fires releasing mercury from vegetation and soil, changing precipitation and wind patterns, and warming oceans. A particularly significant risk exists in the Arctic, where thawing permafrost could release vast quantities of accumulated mercury, potentially undermining decades of progress in pollution control and posing new risks to public health and ecosystems.