In California, cow poop is a big problem for the climate.

Manure management at California dairy farms accounts for 26% of the state’s point-source methane emissions, a figure equal to the point-source emissions from the oil and gas sector, according to research reported in fall 2019 in Nature.

A single dairy cow can produce around 150 pounds of feces each day. For much of human history, this manure would have been used to fertilize agricultural fields, providing them valuable organic matter and nutrients. But in modern dairy production, cow poop is typically considered a waste product, destined to languish in manure lagoons that release vast amounts of methane, a potent greenhouse gas.

Manure lagoon
Manure lagoon (Photo credit: USDA Natural Resources Conservation Service)

These issues aren’t unique of course to California. Throughout the United States, manure has become an unwanted commodity as farmers have shifted toward synthetic fertilizer. “Over the last several decades, the usage of inorganic [chemical] fertilizer has increased dramatically,” said Linda Schott, an assistant professor at the University of Idaho who studies the impact of livestock manure management on soil health. “It’s a pretty similar trend of the increase of farmable acres.” Productive use of manure, on the other hand, has not increased.

Agriculture’s shift away from manure has roots in World War II, with a dramatic spike in the production of nitrogen – a key ingredient in both explosives and fertilizer. After the war ended, the government turned its attention to feeding a growing population. Generous state funding for research into chemical fertilizer set the stage for widespread adoption. In the post-WWII period, farmers used approximately 2 million tons of chemical fertilizer each year; by 2014, this figure had risen tenfold.

Researcher: ‘Flush and forget method is flawed.’

This shift has climate impacts beyond lagoon-bred methane. Energy-intensive chemical fertilizer production generates its own emissions. Fields treated with synthetics miss out on the mitigation and adaptation benefits of manure application, ranging from enhanced carbon sequestration capacity to improved soil health.

For Schott, the solution lies partially in helping people once again see manure as something to be valued, not wasted. “In the manure-management realm, there’s a lot of us working on this – just changing mindsets and perceptions,” she said.

From night soil to flush-and-forget

In the modern era, ideas about human excrement have followed a similar resource-to-waste trajectory. Anthropologist Nick Kawa became interested in how different cultures handle their poop when he was studying Brazilian farms located on Amazonian dark earth, a rich soil that owes much to centuries of composting and treatment with manure – some of it human-derived. Today, he encourages his students at Ohio State University to consider the role of feces in broader social and ecological systems.

“People have been managing what’s referred to as ‘night soil’ for thousands of years, and entire economies have been built around it. Up until the 1970s, in parts of China, when somebody would come to collect your so-called waste, they’d pay you for it,” he said. “That’s just a fundamentally different way of thinking about it.”

Others agree that it’s time to reconsider people’s relationship to their excreta. “Waste absolutely is a resource that, when managed effectively, is not a toxic substance,” said Gabby Black, a researcher at the University of California, Davis, whose Ph.D. focused on the chemistry of treated sewage. “The flush-and-forget treatment method is flawed. It was developed for good reason, but we need to rethink how we treat and reuse our waste in the developed world.”

Mitigation and adaptation in sanitation

One organization working on these issues is the Sustainable Sanitation Alliance (SuSanA), a global network dedicated to incorporating a wide range of social and environmental considerations into the sanitation and waste management sectors. In the past few years, it has added climate change to its list of priorities.

Conventional sewer systems emit greenhouse gases both directly and indirectly. Direct emissions result when feces decompose in settings where no oxygen is present (e.g., treatment ponds and landfills). Indirect emissions include, among others, those generated by the fossil fuels burned to power energy-intensive sewer infrastructure and produce the chemical fertilizers used in lieu of excreta-based crop nutrients.

According to Kim Andersson, a sanitation expert at the Stockholm Environment Institute who helps lead SuSanA’s climate work, more research is needed to understand emissions from different sanitation systems and determine exactly which mitigation efforts would have the greatest impact. “For example, there are major uncertainties about emissions from on-site sanitation systems (such as septic tanks, soak pits, and pit latrines),” he wrote in an email.

But the broad outlines of how to reduce the sector’s emissions are known. Feces, and the infrastructure that manages it, can be used to create renewable energy in the form of biogas, heat recovery, or hydropower (through turbines in wastewater systems); this energy can, in turn, help power sewer systems. Excreta can even be turned into a solid fuel; in Kenya, one local sanitation utility makes poop-based briquettes for use instead of charcoal for cooking. To avoid emissions generated when sewage is land-filled or incinerated, and when fertilizers are produced, treated feces can be applied to agricultural fields or used as a soil amendment in other settings such as forests.

Conventional sewer systems also pose challenges from a climate adaptation perspective. Flooding and extreme weather events can overwhelm wastewater infrastructure, as was seen during Hurricane Sandy, when billions of gallons of sewage spilled into waterways around New York City.

Hurricane Sandy damage
Aftermath of Hurricane Sandy. (Photo credit: Pamela Andrade / Flickr)

Flush-based systems also consume vast amounts of fresh water – an increasingly precious commodity in a warming world. “The amount of water that we pollute with our waste is incredible,” said Gabby Black. “And that’s all drinking water-quality water; we don’t use graywater to flush our toilets unless you live in a super-sophisticated new building.”

Food security is another adaptation-related concern. Soil amendments derived from human poop can improve soil health, an important consideration as rising temperatures and changing weather patterns put new stresses on agricultural production.

Container-based toilets

Sanitation’s mitigation and adaptation challenges aren’t limited to wealthy countries with elaborate sewer systems. Around the world, 700 million city-dwellers lack access to adequate bathroom facilities, according to the Sustainable Sanitation Alliance. Of this number, 80 million are forced to relieve themselves in the open. Providing safe, dignified waste management for everyone while minimizing climate risks requires careful consideration.

“Globally, there has been a strong focus on ‘People need a toilet.’ The big thing has been to promote access to toilets,” said Kim Andersson. “[But] we also have to make sure that the toilet doesn’t contribute to the vulnerability of communities – that you have one flood and then they will not be able to use it, or that it pollutes their environment and drinking water sources.”

One nonprofit in Haiti has spent more than a decade working through these issues. In a country where inadequate sanitation played a key role in a deadly cholera outbreak, SOIL has developed and deployed more than 1,000 waterless, container-based household toilets specially designed to prevent leakage and contamination during floods and other disasters.

Each week, the containers are collected by SOIL staff, a system that creates stable jobs in the local community and avoids households needing to handle their own excreta. The waste is then brought to a treatment facility where contents are transformed into compost through a natural process that relies on heat-loving microbes. This compost is then applied to agricultural fields or used in soil restoration projects.

SOIL Executive Director Sasha Kramer holds a Ph.D. in ecology from Stanford, and the organization has collaborated with a number of scientists to better understand its systems and their impact. Gabby Black helped confirm that its thermophilic composting process eliminates the human gut bacteria and pathogenic bacteria present in untreated feces. Rebecca Ryals, an environmental scientist at the University of California, Merced, has studied the climate mitigation and adaptation implications of its work.

In one project, Ryals worked with postdoctoral researcher Gavin McNicol to compare emissions from SOIL’s composting operations to those from a near-by government-run waste stabilization pond, as well as a grass field where untreated waste is regularly dumped. Their team’s findings: the compost piles produced significantly fewer greenhouse gases.

More recently, Ryals looked at how different compost management strategies might further reduce SOIL’s emissions, and at how soil compost additions affect plant growth over time.

Poop and policy

Ryals first became interested in feces management when researching soil carbon sequestration. She’s now convinced that sanitation deserves more attention within the climate community. “All these things are very connected and important, and also super unappreciated in the world of climate change and climate change solutions.”

Andersson of SuSanA agrees. “We have been studying policy and climate finance, and [sanitation] is not really considered. If we look at the whole portfolio of Green Climate Fund, for example, there is a very small percentage of even the water-related investments that go into sanitation.”

Poop isn’t normally a topic of polite conversation. But as the world looks for ways to prevent the worst outcomes of climate change, this attitude may need to change.

Sarah Wesseler is a Brooklyn-based writer focusing on cities, culture, and climate change.