Agriculture plays a surprising role in carbon dioxide fluctuations

It’s long been recognized that carbon dioxide concentrations in our atmosphere are continuously on the rise. This increase is a byproduct of human activity and an agent of climate change.

However, a less explored but puzzling trend is the growing gap between the highest and lowest annual carbon dioxide levels in the atmosphere.

This widening gap between the peaks and troughs of carbon dioxide concentration was previously attributed to rising temperatures and increased atmospheric carbon dioxide. However, a recent study explores another possible factor: agriculture.

The unexpected findings revise our concept of the carbon cycle and hold important implications for future climate change mitigation efforts.

How agriculture shifts carbon dioxide

The researchers found that, contrary to previous beliefs, nitrogen fertilizer used in agriculture is the chief contributor to the yearly ebb and flow of the carbon cycle. This highlights the impact of our actions and land management decisions on Earth system processes.

Study lead author Danica Lombardozzi is an assistant professor of ecosystem science and sustainability at Colorado State University.

“These findings are important because we have undervalued the role of agriculture in carbon cycle fluxes,” said Lombardozzi.

“A lot of people recognize that agriculture can help mitigate climate change, but because it’s not represented in most Earth system models, it’s not considered in climate change projections the way it should be.”

So, how does this all work? As plants sprout in the spring, they absorb carbon dioxide from the atmosphere to support the new growth. Once crops are harvested and other plants become dormant in the fall, less carbon dioxide is needed by plants and so the level in the atmosphere rises again.

Nitrogen, a common ingredient in fertilizer, is essential for plant growth and thus contributes to increased carbon absorption from the atmosphere during the growing season.

Carbon dioxide by the numbers

The study reveals that agricultural nitrogen contributes 45% to the rise in annual carbon cycle fluctuations.

Increased atmospheric carbon dioxide and warmer temperatures also contribute to the difference between high and low carbon dioxide levels within a year, but not to the extent that nitrogen fertilizers do.

Interestingly, this carbon cycle fluctuation caused by crop growth doesn’t directly affect carbon storage. This is because crops are harvested annually and the absorbed carbon returns to the atmosphere.

However, the study adds an exciting dimension: modifying agricultural practices can enhance long-term carbon storage in the soil, which is a potential weapon against climate change.

Agricultural practices and carbon fluxes

Gretchen Keppel-Aleks, a co-author of the study from the University of Michigan, emphasized the implications of these findings.

“Agricultural management practices are very important to shaping the world we live in,” she said Keppel-Aleks.

“At a time when many people feel like climate change has had profound and negative impacts on their lives through wildfire, flooding or droughts, we can use the fact that this study shows that agricultural management has a profound impact on carbon fluxes to think about how we can use agricultural management to our advantage.”

In line with this, many farmers are turning to regenerative agriculture – agricultural practices designed to improve soil health and crop yield while combating climate change.

Updating Earth system models

Despite evidence showing the crucial role of agriculture in carbon cycle fluctuations, it has been largely overlooked in the past because traditional Earth system models did not include agricultural processes.

The researchers used the Community Earth System Model, a tool developed by the National Center for Atmospheric Research and other institutions, to pinpoint the causes of fluctuation increase. Unsurprisingly, agricultural nitrogen emerged as the key player.

Accounting for agriculture, specifically agricultural nitrogen, in Earth system models is essential for a comprehensive understanding of the carbon cycle. Yet, the majority of the models do not take it into account.

“It is really hard to represent human decisions in an Earth system model, but we need to tackle it,” Lombardozzi said.

The research paints an empowering picture of agriculture’s role in climate change, along with its potential for significant impact on mitigation strategies.

The full study was published in the journal Nature Communications.

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