Full Breakdown
Methane Emissions from California Reservoirs: An Emerging Concern
4/16/2026, 12:39:38 AM
Overview of the Issue
Methane, a significant contributor to climate change, is being emitted from various sources, including the oil and gas industry, landfills, and dairy farms. However, a lesser-known source is California's reservoirs, where decaying organic matter underwater generates methane that bubbles to the surface. Currently, California does not monitor these emissions, prompting a coalition of environmental groups, including Friends of the River and Tell the Dam Truth, to petition the California Air Resources Board (CARB) for regulatory oversight.
Environmental Groups' Petition
The coalition submitted a petition urging CARB to require reports on greenhouse gas emissions from dams and reservoirs. They argue that the unaccounted methane emissions from these water bodies represent a "blind spot" in California's climate strategy, which aims to reduce methane emissions to 40% below 2013 levels by 2030. Keiko Mertz, policy director of Friends of the River, emphasized the importance of addressing this issue, stating, “You can’t have such a potent greenhouse gas just going unaccounted for.”
Scientific Insights and Estimates
Research indicates that reservoirs contribute significantly to methane emissions. The U.S. Environmental Protection Agency (EPA) reported in 2024 that "flooded lands," including reservoirs, are a major source of methane, estimating emissions from these areas at 44.4 million metric tons of carbon dioxide equivalent in 2022. Studies suggest that the methane emitted from the world’s dams ranges between 10 million and 22 million metric tons annually, accounting for approximately 3% to 7% of total human-caused methane emissions.
Challenges in Measurement
Estimating methane emissions from reservoirs poses unique challenges. Unlike emissions from landfills or natural gas wells, methane from reservoirs is more dispersed, making it difficult for satellite sensors to detect. However, advancements in aerial monitoring technology are expected to improve detection capabilities in the coming years.
Perspectives on Regulation
While some experts, like John Harrison from Washington State University, advocate for better data to inform hydropower decisions and emissions management, others express skepticism about the feasibility of reducing emissions from reservoirs. Steven Hamburg, chief scientist at the Environmental Defense Fund, noted that while having more information is beneficial, strategies for mitigating emissions from reservoirs are less clear compared to other sources.
Official Responses
The California Air Resources Board plans to respond to the environmental groups' petition by the end of July. CARB spokesperson Lindsay Buckley acknowledged the petition's significance, stating, “This petition raises important questions that CARB would like to consider.”
Conclusion
As California strives to meet its climate goals, the emissions from reservoirs present a complex challenge that requires further investigation and regulatory action. The ongoing discussions among scientists, environmental groups, and regulatory bodies will shape the future of hydropower and its environmental impact in the state.
Verbatim Quotes
- “You can’t have such a potent greenhouse gas just going unaccounted for,” — Keiko Mertz, Policy Director, Friends of the River
- “In building any new facilities, we want to carefully look at those impacts and minimize them.” — Steven Hamburg, Chief Scientist, Environmental Defense Fund
- “the value of having higher quality data is unclear to me.” — Steven Hamburg, Chief Scientist, Environmental Defense Fund
- “This petition raises important questions that CARB would like to consider,” — Lindsay Buckley, Spokesperson, California Air Resources Board
