The intersection of freshwater and climate is a frequently ignored but critical element of the climate problem, according to a new study from Sweden that explores the link and offers solutions that will help lower emissions. 

Two years in the making, the study, “The Essential Drop to Reach Net-Zero: Unpacking Freshwater’s Role in Climate Change Mitigation,” published by the Stockholm Resilience Centre, identifies forests and freshwater wetlands as a crucial depository of carbon. More than 30 percent of estimated global carbon emissions are sequestered in wetlands. So the need to protect and restore them is urgent. 

“The global water supply is the bloodstream of the Earth and the foundation of any successful mitigation action, since Earth’s climate system and water cycle are deeply intertwined,” said  Malin Lundberg Ingemarsson, program manager at the Stockholm International Water Institute and the study’s lead author. “Ours is the first-ever summary of current research on the role of water in climate mitigation.”

Swamps, bogs and marshes cover 118,000 square miles in the U.S., an area larger than the state of Arizona. More than half of the wetlands the U.S. originally held have been lost due to farming and development, even though wetlands have one of the highest stores of soil carbon in the Earth’s biosphere. The best known wetland in the U.S. is the Florida Everglades. Despite its vast expanse, the Everglades is only 50 percent of its original size—much has been drained for development. Other famous wetlands include the Okavango Delta in Botswana, the Mekong Delta in Vietnam and the Pantanal, an area of Bolivia, Brazil and Paraguay which covers an area larger than England.

“Water is continuously overlooked in discussions about climate,” said  Juliet Christian-Smith, Western States Regional Director at the Union of Concerned Scientists, who was not involved in the study. “This report gives great advice. It’s very unwise not to consider water as part of the solution.”

The study also concludes that water loss caused by climate change can severely affect power production. Dams with poor siting, design and management can result in lower power generation and higher climate emissions. 

Drought conditions in the Southwest, long predicted by climate experts, threatens hydropower production at Lake Mead and Hoover Dam in Nevada and Arizona, for example, where water levels are at their lowest since 1937, when the reservoir was first filled.

Lake Mead is currently at 27 percent capacity, according to NASA. Hydropower is a vital source of alternative energy and generates power without climate emissions. Freshwater is also vital for other forms of carbon-free energy production, such as nuclear power plants, which need freshwater for cooling. Over the summer, two reactors in France were shut down entirely because prolonged drought reduced the amount of available cooling water. Several other French nuclear plants along the Rhone and Garonne Rivers were forced to reduce their output.

The transition to renewable energies can reduce the pressure and effects on water resources from energy production, largely due to the low water demands of solar and wind.

The study also examines wastewater as a major source of emissions, both from treatment plants and untreated waste. Greenhouse gases, primarily methane, are created by biological processes taking place in untreated wastewater. In the U.S., wastewater also contains nitrogen and phosphorus from human waste, food, fertilizer, soaps and detergents.

More than 2 million people in the U.S. live without access to adequate wastewater infrastructure. By some estimates, nearly half of wastewater released into the global environment is untreated. Treatment plants globally account for roughly 3 percent of greenhouse gas emissions.

Emissions from wastewater treatment plants, however, can be cut with improved design and management, the study says. Energy efficiency measures can lower emissions, and wastewater plants can install anaerobic digesters that produce methane, which can be burned for heat and power.

Much of the wastewater from cities and rural areas around the world is either untreated or partially treated, and emissions from untreated sewage is an estimated three times higher than emissions from conventional wastewater treatment plants. The expansion of wastewater collection and treatment systems will be critical to reducing climate change in the future, according to the study.

“Water is rarely taken into account when we look for climate solutions,” said Ingemarsson. “We need to take an integrated approach. We can no longer work in silos.”

Looking forward, Ingemarsson called for further research in the role water plays in climate mitigation and hopes for broader dissemination of the study, especially at an important U.N. conference on water in New York in March 2023. It will be the most important water conference of its kind since the 1970s.

This study led by Ingemarsson, included contributions from the Potsdam Institute for Climate Impact Research (PIK), the Stockholm Resilience Centre (SRC), Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ), and the United Nations Development Programme (UNDP). 

Charlie Miller is a writer living in Baltimore who covers climate change and other environmental issues.