Drought, soil desiccation cracking, and carbon dioxide emissions: an overlooked feedback loop exacerbating climate change
Soil stores 80 percent of carbon on earth, yet with increasing cycles of drought, that crucial reservoir is cracking and breaking down, releasing even more greenhouse gases creating an amplified feedback loop that could accelerate climate change.
The accuracy of climate models depends on many factors -- greenhouse gas emissions from industrial and transportation activity, farm animal "emissions," urban growth and loss of forests, and solar reflections off snow and ground cover. Natural phenomena like volcanic eruptions also contribute and are incorporated into models.
However, some other natural processes have been overlooked. Farshid Vahedifard, professor and Louis Berger Chair in civil and environmental engineering, points to an important one that lies directly beneath our feet and covers most of our planet above water.
In a study published in Environmental Research Letters, Vahedifard notes that soil stores 80 percent of carbon on Earth, and with increasing cycles and severity of droughts in several regions, that crucial reservoir is cracking and breaking down, releasing even more carbon dioxide and other greenhouse gases into the atmosphere.
In fact, it may be creating an amplified feedback loop that could accelerate climate change well beyond current predictions."This process has not been sufficiently evaluated in the existing literature or incorporated into models," said Vahedifard. "If we don't consider the interplay of drought, soil desiccation cracking, and CO2 emissions, that could result in significant inaccuracies when modeling and predicting climate change. There are other repercussions as well. Poorer soil health can lead to reduced photosynthesis and lower carbon dioxide uptake, and it can compromise the structural integrity of earthen dams that protect against floods."
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But soil changes caused by drought could be as significant, if not more significant, than any of those factors. Drought, manifested by long periods of low soil moisture content and high temperature, leads to cracking in fine-grained soils, sometimes extending meters below the surface. The cracks result in more exposure to the air, increased microbial activity and breakdown of organic matter, released carbon dioxide, and loss of nutrients and ability to support plant growth, reducing carbon dioxide sequestering.
The deep cracks expose much older reserves of carbon that had previously been stable and protected. The permeation of air into the soil accelerates the release of not only carbon dioxide from organic matter but also other greenhouse gases like nitrous oxide.
Small animals like earthworms and millipedes that help turn the soil over are also affected by the reduced moisture and increased air exposure, being less able to play active roles in nutrient cycling and soil structure maintenance. That, in turn, increases the likelihood of soil cracking and aeration.
"The amplifying effect of soil carbon feedback loops and its interactions with other loops could carry us across tipping points and lead to even more severe and permanent shifts in climate," said Vahedifard.
more:
https://www.sciencedaily.com/releases/2024/03/240313135541.htm
