New! Sign up for our email newsletter on Substack.

Study: Soils Could Release Much More Carbon Than Expected as Climate Warms

Soils could release much more CO2 than expected into the atmosphere as the climate warms, according to new research by scientists from the Department of Energyโ€™s Lawrence Berkeley National Laboratory (Berkeley Lab).

Their findings are based on a field experiment that, for the first time, explored what happens to organic carbon trapped in soil when all soil layers are warmed, which in this case extend to a depth of 100 centimeters. The scientists discovered that warming both the surface and deeper soil layers at three experimental plots increased the plotsโ€™ annual release of CO2 by 34 to 37 percent over non-warmed soil. Much of the CO2 originated from deeper layers, indicating that deeper stores of carbon are more sensitive to warming than previously thought.

They report their work online March 9 in the journal Science.

The results shed light on what is potentially a big source of uncertainty in climate projections. Soil organic carbon harbors three times as much carbon as Earthโ€™s atmosphere. In addition, warming is expected to increase the rate at which microbes break down soil organic carbon, releasing more CO2 into the atmosphere and contributing to climate change.

But, until now, the majority of field-based soil warming experiments only focused on the top five to 20 centimeters of soilโ€”which leaves a lot of carbon unaccounted for. Experts estimate soils below 20 centimeters in depth contain more than 50 percent of the planetโ€™s stock of soil organic carbon. The big questions have been: to what extent do the deeper soil layers respond to warming? And what does this mean for the release of CO2 into the atmosphere?

โ€œWe found the response is quite significant,โ€ says Caitlin Hicks Pries, a postdoctoral researcher in Berkeley Labโ€™s Climate and Ecosystem Sciences Division. She conducted the research with co-corresponding author Margaret Torn, and Christina Castahna and Rachel Porras, who are also Berkeley Lab scientists.

โ€œIf our findings are applied to soils around the globe that are similar to what we studied, meaning soils that are not frozen or saturated, our calculations suggest that by 2100 the warming of deeper soil layers could cause a release of carbon to the atmosphere at a rate that is significantly higher than today, perhaps even as high as 30 percent of todayโ€™s human-caused annual carbon emissions depending on the assumptions on which the estimate is based,โ€ adds Hicks Pries.

The need to better understand the response of all soil depths to warming is underscored by projections that, over the next century, deeper soils will warm at roughly the same rate as surface soils and the air. In addition, Intergovernmental Panel on Climate Change simulations of global average soil temperature, using a โ€œbusiness-as-usualโ€ scenario in which carbon emissions rise in the decades ahead, predict that soil will warm 4ยฐ Celsius by 2100.

To study the potential impacts of this scenario, the Berkeley Lab scientists pioneered an innovative experimental setup at the University of Californiaโ€™s Blodgett Forest Research Station, which is located in the foothills of Californiaโ€™s Sierra Nevada mountains. The soil at the research station is representative of temperate forest soils, that in turn account for about 13.5 percent of soil area worldwide.

The scientists built their experiment around six soil plots that measure three meters in diameter. The perimeter of each plot was ringed with 22 heating cables that were vertically sunk more than two meters underground. They warmed three of the plots 4ยฐ Celsius for more than two years, leaving the other three plots unheated to serve as controls.

They monitored soil respiration three different ways over the course of the experiment. Each plot had an automated chamber that measured the flux of carbon at the surface every half hour. In addition, one day each month, Hicks Pries and the team measured surface carbon fluxes at seven different locations at each plot.

A third method probed the all-important underground realm. A set of stainless steel โ€œstrawsโ€ was installed below the surface at each plot. The scientists used the straws to measure CO2 concentrations once a month at five depths between 15 and 90 centimeters. By knowing these CO2 concentrations and other soil properties, they could model the extent to which each depth contributed to the amount of CO2 released at the surface.

They discovered that, of the 34 to 37 percent increase in CO2 released at the three warmed plots, 40 percent of this increase was due to CO2 that came from below 15 centimeters. They also found the sensitivity of soil to warming was similar across the five depths.

The scientists say these findings suggest the degree to which soil organic carbon influences climate change may be currently underestimated.

โ€œThereโ€™s an assumption that carbon in the subsoil is more stable and not as responsive to warming as in the topsoil, but weโ€™ve learned thatโ€™s not the case,โ€ says Torn. โ€œDeeper soil layers contain a lot of carbon, and our work indicates itโ€™s a key missing component in our understanding of the potential feedback of soils to the planetโ€™s climate.โ€

The research was supported by the Department of Energyโ€™s Office of Science.

Fuel Independent Science Reporting: Make a Difference Today

If our reporting has informed or inspired you, please consider making a donation. Every contribution, no matter the size, empowers us to continue delivering accurate, engaging, and trustworthy science and medical news. Independent journalism requires time, effort, and resourcesโ€”your support ensures we can keep uncovering the stories that matter most to you.

Join us in making knowledge accessible and impactful. Thank you for standing with us!



1 thought on “Study: Soils Could Release Much More Carbon Than Expected as Climate Warms”

  1. We will have to reduce CO2 emissions by 200%. No new emission from fossil energy, filter CO2 out of the atmosphere, split it to C and O. Requires 8 kWh per kg, 1 million squarekilometer photovoltaic in a sunny desert for 36 billion tons a year.

    Reply

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.