The amount of nitrous oxide (N2O) in the atmosphere may increase as the climate continues to warm.
Researchers from the University of Minnesota have recorded the nitrous oxide levels every hour for six years from a tower 200 meters in the air, and found that the levels recorded were highest during the warmest years.
While current models estimate nitrous oxide from direct sources like fertilizer application, the researchers found that indirect emissions from streams and ditches were also a large source of nitrous oxide that showed significant seasonal and internal variability. This demonstrated that the regional emission factor is highly sensitive to climate.
During 2012, the warmest year in the six-year study, the researchers found that the emission factor was 7.5 percent, nearly double that of previous reports. They also found that indirect emissions associated with runoff and leaching dominated the interannual variability of total emissions.
The researchers used long-term measurements and modeling to suggest that emissions will likely increase significantly as temperature and precipitation increases.
The problem is often exacerbated by increased heavy rains associated with climate warming, as more rain means more nitrogen running off into waterways where it can be converted in to nitrous oxide.
In Minnesota and many other areas, rain is increasing in the spring when fertilizers are applied, worsening the problem because the bacteria that converts the nitrogen into nitrous oxide are also more active in warmer and wetter soils.
A nitrous oxide molecule is nearly 300 times more effective than carbon dioxide in terms of warming the planet. The greenhouse gas comes from many different sources, including emissions from farm fields and associated runoff.
The researchers wrote in the study that they fully expect the impact of nitrous oxide to continue to rise.
“Under current trends in climate and anthropogenic [nitrogen] use, we project a strong positive feedback to warmer and wetter conditions and unabated growth of regional N2O emissions that will exceed 600 Gg N2O-N⋅y−1, on average, by 2050,” the study states. “This increasing emission trend in the US Corn Belt may represent a harbinger of intensifying N2O emissions from other agricultural regions.”
The study was published in the Proceedings of the National Academy of Sciences of the United States of America.