Global deforestation directly linked to atmospheric mercury emissions

A recent study has unveiled a startling connection between deforestation and mercury emissions, shedding light on a largely overlooked environmental challenge.

The research from MIT reveals that global deforestation is responsible for approximately 10 percent of human-made mercury emissions annually, emphasizing the critical role of the world’s forests, from the Amazon rainforest to the savannahs of sub-Saharan Africa, in purifying the air of this toxic pollutant.

Overlooked link between deforestation and mercury emissions

Ari Feinberg, the study’s lead author and a former postdoctoral researcher at the Institute for Data, Systems, and Society (IDSS), highlighted the significance of this finding, particularly for tropical regions.

“We’ve been overlooking a significant source of mercury, especially in tropical regions,” says Feinberg.

The study demonstrates that the Amazon rainforest alone contributes about 30 percent to the global land mercury sink. This underscores the importance of halting Amazon deforestation as a means to significantly mitigate mercury pollution.

Moreover, the research team, which includes Noelle Selin, Martin Jiskra, Pasquale Borrelli, and Jagannath Biswakarma, found that global reforestation efforts could increase mercury uptake by an estimated 5 percent annually.

While reforestation is crucial, the team stresses that it cannot replace the need for comprehensive pollution control efforts worldwide.

Selin, a professor at IDSS and the Department of Earth, Atmospheric and Planetary Sciences at MIT, points out the urgency of integrating deforestation-related emissions into broader environmental policies.

This is especially true given the substantial contribution of these emissions to the global mercury problem.

The crucial role of forests

Historically, the focus on deforestation has predominantly been on its role in carbon dioxide emissions. However, this study brings to light the terrestrial biosphere’s significant yet underappreciated role in the global mercury cycle.

Mercury, unlike carbon dioxide, does not serve a biological function for plants but is instead absorbed by leaves and eventually transferred to the soil, where it is more securely contained.

This process helps mitigate the risk of mercury entering water bodies and becoming methylmercury, a potent neurotoxin that poses significant risks to human health through the consumption of contaminated fish.

Feinberg further explains the vital ecosystem service provided by forests in sequestering mercury, thereby reducing the prevalence of toxic methylmercury in oceans.

“In soils, mercury is much more tightly bound than it would be if it were deposited in the ocean. The forests are doing a sort of ecosystem service, in that they are sequestering mercury for longer timescales,” says Feinberg.

Methodology and key findings

Despite the attention on industrial mercury sources, such as fossil fuel combustion and small-scale gold mining, the impact of deforestation had not been adequately considered until this study.

The research utilized a sophisticated chemical transport model to examine mercury emissions resulting from deforestation across various global regions.

Overcoming challenges in data collection, particularly in heavily deforested regions like tropical Africa and Southeast Asia, the team employed innovative modeling techniques to enhance their understanding of deforestation’s impact on mercury emissions.

The findings are stark: about 200 tons of mercury are emitted annually due to deforestation, accounting for a significant portion of total human-made emissions.

In countries like Brazil, deforestation emissions comprise an even larger share, highlighting the urgent need for targeted policy interventions.

Feinberg’s comparison of deforestation to the world’s second-highest mercury emitter, after China, underscores the gravity of the situation.

Lowering mercury emissions by reducing deforestation

As the Minamata Convention seeks to address primary mercury emissions, the role of deforestation is poised to become increasingly significant.

Selin emphasizes the interconnectedness of environmental systems and the need for holistic understanding and solutions.

“Policies to protect forests or cut them down have unintended effects beyond their target. It is important to consider the fact that these are systems, and they involve human activities, and we need to understand them better in order to actually solve the problems that we know are out there,” Selin says.

In summary, this eye-opening study illuminates the critical but often overlooked link between deforestation and mercury emissions, revealing that forests play a vital role in mitigating air pollution by absorbing a significant portion of human-made mercury.

Highlighting the Amazon’s pivotal contribution and calling for global reforestation efforts, this important research underscores the necessity of integrating deforestation-related emissions into comprehensive environmental policies.

The work of Ari Feinberg and his team shifts the narrative on the environmental impact of deforestation and serves as a call to action for policymakers, researchers, and the global community to adopt a holistic approach to environmental stewardship, ensuring the preservation of our planet’s forests and the health of its ecosystems for future generations.

The full study was published in the journal Environmental Science & Technology.

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