An international group of researchers has discovered that nitrogen emissions resulting from fertilizers and fossil fuels contribute to a net cooling influence on the climate. However, they caution that rising nitrogen levels in the atmosphere have additional harmful environmental effects, urging an immediate reduction in greenhouse gas emissions to combat global warming.
A global research team has revealed that nitrogen emissions from fertilizers and fossil fuels have a net cooling effect on our climate. Nonetheless, they caution that increased atmospheric nitrogen poses significant environmental risks, calling for swift action to cut greenhouse gas emissions and address global warming.
Published today in Nature, this study indicates that reactive nitrogen entering the environment through human activity results in a cooling effect of minus 0.34 watts per square meter. Although global warming would have progressed at a greater pace without human-induced nitrogen emissions, this nitrogen does not compensate for the greenhouse gases that are warming the atmosphere.
The research was led by the Max Planck Institute in Germany, with contributions from the University of Sydney. This finding arrives just after new information from the European Union’s Copernicus Climate Change Service reported that Sunday, July 21, marked the hottest day recorded in recent history.
The net cooling impact arises through four mechanisms:
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Short-lived nitrogen oxides created during fossil fuel combustion pollute the air by generating fine particles that reflect sunlight, which cools the climate;
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ammonia, a compound of nitrogen and hydrogen, released into the atmosphere from manure and synthetic fertilizers has a similar cooling effect;
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applying nitrogen to crops promotes plant growth, which enhances the absorption of CO2 from the atmosphere, contributing to a cooling effect;
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nitrogen oxides also assist in breaking down atmospheric methane, a very powerful greenhouse gas.
The researchers cautioned that an increase in atmospheric nitrogen is not an effective strategy for fighting climate change.
“Nitrogen fertilizers are harmful to water quality, and nitrogen oxides from fossil fuels contaminate the air. Hence, elevating nitrogen levels in the atmosphere as a means to address climate change is neither an appropriate compromise nor a viable solution,” explained Professor Federico Maggi from the University of Sydney’s School of Civil Engineering.
Sönke Zaehle from the Max Planck Institute noted: “While this may seem like encouraging news, it’s essential to recognize that nitrogen emissions carry numerous adverse effects, such as impacts on health, biodiversity, and the ozone layer. Thus, the current results should not excuse the negative consequences or suggest that additional nitrogen is a viable strategy against global warming.”
Elemental nitrogen, which constitutes about 78 percent of the air, is neutral in terms of climate impact. Nevertheless, other forms of reactive nitrogen can indirectly or directly influence global climate—sometimes contributing to warming and other times to cooling. Nitrous oxide (N2O) is nearly 300 times more effective as a greenhouse gas than CO2, while various nitrogen compounds can promote tropospheric ozone formation, intensifying global warming.
Professor Maggi emphasized the importance of this research in understanding how nitrogen emissions from agriculture impact the climate.
“This work exemplifies how complex planetary-level interactions cannot be accurately captured with overly simplistic assessment tools. It underscores the necessity of developing mathematical models to portray the emergence of nonlinear, or disproportionately large, effects across soils, land, and the atmosphere,” he stated.
“Even though it might appear counterintuitive, introducing reactive nitrogen into the environment, primarily as agricultural fertilizers, can lower overall warming. However, this is minimal compared to the significant reductions in greenhouse gas emissions needed to maintain the planet within safe operational limits.
“Cutting-edge computational tools are advancing our understanding of climate change science, but comprehension alone isn’t sufficient—we must urgently act to cut down greenhouse gas emissions.”
Achieving a Comprehensive Understanding of Nitrogen’s Impacts
The scientists assessed the total effects of nitrogen from human activities by first quantifying the various nitrogen compounds found in soil, water, and air.
They then integrated this information into models representing the global nitrogen cycle and its interactions with the carbon cycle, including how it promotes plant growth and affects CO2 and methane levels in the atmosphere. Based on these simulations, they used another atmospheric chemistry model to evaluate the impact of human-created nitrogen emissions on radiative forcing—the energy that strikes one square meter of Earth’s surface over time.
