A new study led by Colorado State University has uncovered a surprising factor driving seasonal fluctuations in atmospheric carbon dioxide: agriculture. While the overall rise in carbon dioxide levels is well-documented and attributed to human activities and climate change, the increasing gap between annual peaks and lows in carbon dioxide levels was previously thought to be driven primarily by rising temperatures and elevated carbon dioxide concentrations. However, researchers now reveal that agricultural nitrogen fertilizer plays the most significant role in these seasonal shifts.
The study, published in Nature Communications, found that nitrogen-based fertilizers are responsible for 45% of the fluctuation increase in the annual carbon cycle, surpassing the influence of atmospheric carbon dioxide (40%) and rising temperatures (18%).
Lead researcher Danica Lombardozzi, an assistant professor of ecosystem science and sustainability, highlighted that while agriculture is often seen as a tool for climate change mitigation, its role in carbon cycle fluxes has been underestimated. According to Lombardozzi, agricultural processes have not been properly integrated into Earth system models, meaning climate projections may not fully account for their impact.
The annual carbon cycle reflects the balance of carbon dioxide absorbed and released by the biosphere. During spring and summer, plants, including crops, absorb carbon dioxide from the atmosphere to grow. After harvest, plant respiration slows, and carbon dioxide levels rise again.
However, modern agricultural practices, particularly the widespread use of nitrogen fertilizers, have amplified these fluctuations. Fertilizer use increases crop growth and carbon absorption, but since crops are harvested annually, the stored carbon is quickly released back into the atmosphere rather than being sequestered in the soil.
Despite the lack of long-term carbon storage from crops, experts suggest that agricultural management practices can be adapted to promote carbon sequestration in soils, potentially aiding climate change mitigation efforts.
Gretchen Keppel-Aleks, an atmospheric scientist at the University of Michigan and co-author of the study, emphasized the significance of these findings. With climate change already impacting lives through extreme weather events such as wildfires, floods, and droughts, understanding how agricultural management influences carbon cycles presents an opportunity to use these practices for environmental benefit.
The research team used the Community Earth System Model, developed by the National Center for Atmospheric Research, to analyze the sources of carbon cycle fluctuations. Unlike traditional Earth system models, this advanced model incorporates agricultural processes, allowing scientists to quantify the impact of nitrogen fertilizers more accurately.
Lombardozzi emphasized the urgent need for Earth system models to incorporate agricultural factors, particularly nitrogen fertilizers, to fully understand carbon cycle dynamics. Representing human decisions in climate models is a complex challenge, but tackling this issue is essential for accurately assessing and mitigating climate change.
As scientific understanding of agriculture’s role in the carbon cycle continues to evolve, the findings from this study highlight the need for policy and management strategies that recognize the power of sustainable farming practices.
The study provides valuable insights into how agricultural practices influence global carbon levels and highlights the need for better integration of farming activities into climate projections.
(Source: Colorado State University)
