Agriculture is the main cause of seasonal carbon ups and downs, according to a recent study led by Colorado State University. While the overall amount of carbon dioxide in the atmosphere has been steadily increasing due to human activities and climate change, the fluctuations between the highest and lowest levels of carbon dioxide each year have also been widening. This trend has been seen as a consequence of warming temperatures and more carbon dioxide, but the new study suggests that agriculture plays a key role in these seasonal variations.
The study, published in Nature Communications, highlights that while climate and carbon dioxide concentrations contribute to annual fluctuations, agricultural nitrogen fertilizer is the most significant cause. This finding underscores the impact of human actions and land management on the Earth’s carbon cycle. Lead author Danica Lombardozzi, an assistant professor of ecosystem science and sustainability, emphasized that agriculture’s role in the carbon cycle has been underestimated. While agriculture is often recognized for its potential to mitigate climate change, it has not been adequately represented in most Earth system models, limiting its inclusion in climate change projections.
The fluctuations in the carbon cycle show how much the biosphere grows each year. In spring, plants draw carbon dioxide from the atmosphere as they grow, and in fall, after crops are harvested and plants go dormant, carbon dioxide levels in the atmosphere rise again. Plants need nitrogen to absorb carbon dioxide and grow, and most crops are fertilized with nitrogen, which is necessary for food production. This nitrogen contributes to greater carbon absorption by plants, causing an increase in carbon flux.
The study found that agricultural nitrogen accounts for 45% of the increase in the annual carbon cycle fluctuations, with rising carbon dioxide contributing 40% and warming temperatures accounting for 18%. While these fluctuations do not directly affect carbon storage, as crops are harvested annually and return the absorbed carbon to the atmosphere, agricultural management practices can be adjusted to store more carbon in the soil over the long term. Such practices could help mitigate climate change by sequestering carbon in the soil, which would reduce the amount of carbon dioxide in the atmosphere.
Agricultural management practices are therefore crucial in shaping the global carbon cycle. With the increasing frequency of extreme weather events like wildfires, flooding, and droughts, the study’s findings offer an opportunity to rethink how agriculture can be used to counteract climate change. Many farmers are already adopting practices known as regenerative agriculture, which focus on improving soil health, enhancing crop production, and simultaneously reducing the carbon footprint of farming.
Previous studies that observed the increasing seasonal differences in carbon dioxide levels had not accounted for the role of agriculture, as earlier Earth system models did not include agricultural processes. However, the research team used the Community Earth System Model, developed by the National Center for Atmospheric Research, which integrates agricultural processes to assess the sources of these fluctuations. The study revealed that agricultural nitrogen is the largest contributor to the increased seasonal variability in carbon dioxide levels.
Earth system models are complex and include global processes related to the atmosphere, land, and oceans, along with their associated chemistry, biology, and physics. The Community Earth System Model is distinct because it incorporates agricultural processes, allowing researchers to assess their effect on the carbon cycle. Lombardozzi stressed that in order to accurately evaluate the carbon cycle, Earth system models must account for agriculture, particularly agricultural nitrogen. However, most current models still fail to include these factors.
Representing human decisions in Earth system models is challenging, but Lombardozzi believes it is necessary for improving our understanding of how agricultural practices influence the carbon cycle and climate change. By integrating agriculture into these models, scientists can gain a more accurate picture of the complex interactions between human activities and the Earth’s climate system, ultimately leading to better-informed strategies for climate change mitigation.
