Toward net-zero emissions nitrogen fertilizers

Washington, DC—Nearly 4 billion people rely on food that is grown using synthetic nitrogen fertilizers, which are made using energy-intensive, greenhouse gas-emitting processes. For the agricultural system to achieve net-zero carbon emissions, new fertilizer strategies will be necessary. New work from Carnegie Staff Associate Lorenzo Rosa and Paolo Gabrielli, a visiting investigator from ETH Zurich, probed various possibilities for achieving this crucial climate goal without creating unintended environmental consequences. Their findings are published in Environmental Research Letters.

For centuries, nitrogen availability limited agricultural productivity. Then, in the early 20th century, a breakthrough technological innovation, called the Haber-Bosch process, enabled the atmospheric nitrogen to react with hydrogen and form ammonia, which could, in turn, be used to synthesize fertilizers.

This technological advancement powered an agricultural boom, improving nutrition and underpinning population growth. But it requires fossil fuels such as natural gas or coal to supply the necessary hydrogen for creating ammonia. As a result, the production of nitrogen fertilizers is responsible for two percent of global energy consumption and emits about 310 megatons of carbon dioxide pollution each year.

Additionally, much of the world is dependent on importing nitrogen fertilizer. Likewise, the natural gas used in the ammonia synthesis process is also often imported. This leaves the global food supply vulnerable to disruptions like pandemics and wars.

“Looking ahead, we will need to double food production around the world by 2050 in order to keep up with population growth,” Rosa said.

“But this increased demand will require us to secure food production against future crises, as well as improving agricultural sustainability to meet our climate goals,” Gabrielli added.

Rosa and Gabrielli analyzed a variety of options for lowering the carbon footprint of the fertilizer industry to net-zero emissions without diminishing the global food supply, including:

• Capturing the carbon produced from ammonia synthesis before it reaches the atmosphere and permanently storing it underground.
• Using biomass to capture and contain the carbon produced by ammonia production.
• Supplying the hydrogen molecules to create ammonia using a process called water electrolysis, which is based on carbon-free electricity.

“These solutions can reduce agriculture’s dependence on fossil fuels, but they will require more land, water, and energy than current methods of nitrogen fertilizer production,” Gabrielli said. “There is no one-size-fits-all solution for every country and different approaches will probably need to be tailored on a case-by-case basis depending on local resources.” 

Added Rosa: “It’s not only about achieving net-zero emissions. It’s about being aware of unintended environmental consequences. We have to be careful about where we deploy these processes to avoid stressing water systems or repurposing natural areas.”

This finding suggests a potential restructuring of the international chemicals trade, with fertilizer production moving from countries with large fossil resources to countries with abundant renewable energy infrastructure, land and water resources.

Rosa and Gabrielli’s work also emphasizes that reducing overall inefficiencies in the agricultural system, including food waste, and adopting less meat-heavy diets, would decrease the need for nitrogen fertilizers and help reduce food production’s carbon footprint. Currently only 20 percent of the fertilizer produced is actually used to grow food and the vast majority is lost or wasted.

This work is a key component in Rosa’s ongoing research in understanding challenges and opportunities in ensuring global food, water, and energy security.  Ecologists at Carnegie are focused on informing the sustainability of the Earth system, including exploring how we can provide sustainable access to energy, food, and water, and how we can deploy climate mitigation strategies sustainably.