The role of food in climate change has emerged as one of the defining challenges of our time. The journey of a steak, fruit or salad from the vast farmlands to the plates on our tables leaves a significant footprint on the environment.
At the heart of this challenge is the prodigious use of fertilizers and the increasing demand for meat from a growing world population.
As earth, climate and atmospheric scientists, we monitor global greenhouse gas emissions and have just published the most comprehensive assessment to date of a potent greenhouse gas from food production: nitric oxide, or N₂O.
After carbon dioxide and methane, N₂O is the most consequential greenhouse gas that humans release into the atmosphere. Although there is less N₂O than carbon dioxide in the atmosphere, it is 300 times more powerful at warming the planet, and remains in the atmosphere for more than a century, trapping heat. Today, atmospheric N₂O levels are about 25% higher than before the Industrial Revolution, and they are still rising at an accelerating rate.
We found that fertilizers and animal manure management are leading the increase in N₂O emissions worldwide and their rapid accumulation in the atmosphere. This is more than a climate problem. N₂O also damages the ozone layer, which protects people from harmful solar radiation. And nitrogen runoff from fields pollutes waterways, increasing harmful algae blooms and creating oxygen-depleted dead zones.
The growth of N₂O emissions is alarming, but people today have the knowledge and many of the technologies needed to reverse the trend.
Where do N₂O emissions come from?
Before the Industrial Revolution, natural sources of N₂O from microbes living in forest soils and in the oceans were approximately equal to natural sinks consuming N₂O in the air, so N₂O concentrations in the atmosphere were relatively constant.
However, the human population and its demand for food have grown rapidly, throwing that natural balance out of control.
We found that human activities alone have increased N₂O emissions by 40% over the past four decades, with agriculture contributing approximately 74% of total anthropogenic N₂O emissions.
The largest human sources of N₂O are agriculture, industry and the burning of forests or agricultural waste.
Nitrogen fertilizers, which are widely used in agriculture, are one of the largest contributors. Fertilizers are responsible for 70% of total N₂O emissions in agriculture worldwide. Animal manure from intensive livestock farming contributes approximately 30%. A smaller source, but one that is growing rapidly, is aquaculture, such as fish farming, especially in China, where it has increased twenty-fivefold in the past forty years.
In addition to agriculture, industrial processes such as the production of nylon, explosives and fertilizers and the combustion of fossil fuels also contribute to N₂O emissions, but to a lesser extent than agriculture.
N₂O emissions by country
Emissions vary widely from country to country for a number of social, economic, agricultural and political reasons.
Emerging economies such as China and India have experienced sharply increasing N₂O trends over the past four decades as they have increased agricultural productivity to meet the food demands of their growing populations.
China is the largest producer and user of fertilizer. The Action Plan for Zero Growth in Fertilizer Use by 2020, released in 2015, has helped reduce these N₂O emissions. However, industrial N₂O emissions have continued to rise.
In Brazil and Indonesia, clearing and burning of forests to make room for crops and livestock, combined with increasingly intensive agricultural practices, has exacerbated nitrogen losses from natural sources and increased greenhouse gas emissions.
Africa has opportunities to increase food production without increasing nitrogen fertilization. However, North African countries have more than tripled their emissions growth over the past two decades, mainly due to substantial growth in livestock populations in Africa.
However, a few regions have managed to reduce some of their N₂O emissions with more sustainable practices.
The European Union, Japan and South Korea have all successfully reduced anthropogenic N₂O emissions over the past four decades, although they are still major emitters on a global scale; The reductions largely come from the chemical industry in the 1990s. Their nitrogen use in agriculture has also become more efficient; however, they still have work to do. Their emissions from direct fertilization and fertilization have decreased only slightly and have recently stabilized.
In the US, agricultural emissions continue to rise, while industrial emissions have declined slightly, leaving overall emissions fairly flat.
How to reduce N₂O emissions
Addressing the challenge of reducing N₂O emissions requires a combination of policy interventions, technological innovation and individual actions. For example:
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Similarly, livestock management innovations such as nutritional supplements and improved waste management practices can reduce the amount of N₂O from livestock.
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Industries, especially nylon and fertilizer manufacturing, can install existing, affordable technologies to reduce nearly all of their N₂O emissions. That’s an easy win for implementation and the climate. Most of the world has already done this, leaving China and the US responsible for most of the remaining industrial emissions of N₂O.
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Consumers can also make plant-based foods a larger part of their diets. You don’t have to go vegan unless you want to, but reducing the frequency and portion sizes of meat and dairy consumption can be healthy for both you and the environment. Environmentally friendly practices such as composting food waste and reducing the use of fertilizer on lawns also help.
Overall, a holistic approach that combines policy, technology and individual actions is needed to tackle N₂O emissions and combat climate change. As governments, industries and citizens all work towards a sustainable future, these strategies can help ensure food security and environmental sustainability for future generations.
This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Hanqin Tian, Boston College; Eric Davidson, University of Maryland, Baltimore; Pep Canadell, CSIROand Rona Louise Thompson, Norwegian Institute for Aerial Research
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Hanqin Tian receives funding from the National Science Foundation and the U.S. Department of Agriculture.
Eric Davidson has received funding from NSF, USDA, DOE, and NASA. He is affiliated with the University of Maryland Center for Environmental Science and Spark Climate Solutions.
Pep Canadell receives funding from the Australian National Environmental Science Program – Climate Systems Hub.
Rona Louise Thompson receives funding from the European Commission through the Horizon Europe Programme.