After nearly 40 years of research, scientists have discovered evidence that challenges long-held assumptions about forest soils. The world’s longest-running soil warming experiment suggests that even carbon, once thought to be stable, can begin to break down as temperatures rise, releasing additional carbon dioxide into the atmosphere.
Jerry Melillo, a distinguished scientist at the Marine Biological Laboratory, has spent the past 37 years studying the hot region of Harvard Forest in central Massachusetts. During the experiment, the researchers kept the soil 5 degrees Celsius warmer than the surrounding ground throughout the year.
Melillo said the research team chose the 5-degree increase because it represented the upper bound of global warming projections when the experiment began decades ago.
“Microorganisms are important components of soil ecosystems because they break down organic matter and recycle elements essential for plant growth,” Melillo explains. “Warming can accelerate the loss of carbon from soils as microbial communities reshape.”
Rising temperatures will change how forest soils store carbon
Decades of experiments allowed researchers to observe how soil reacts over an unusually long period of time. During four decades of warming, it was observed that stable parts of soil organic matter, once thought to be resistant to decomposition due to warming, also began to decompose.
As these long-term carbon stores decompose, additional CO2 is released into the atmosphere. The finding suggests that as warming continues, forest soils may be contributing more carbon to the atmosphere than scientists previously expected.
Average global temperatures have already increased by about 1.1 to 1.4 degrees Celsius since the Industrial Revolution. Melillo points out that future warming will largely depend on actions taken to reduce greenhouse gas emissions.
“The projected increase would be even lower if we significantly reduced carbon dioxide emissions from fossil fuel combustion or reduced deforestation,” Melillo explains.
Better climate models through long-term research
The newly observed stable soil carbon decomposition indicates that climate feedback loops may become stronger. As the Earth warms, soils can release more carbon, which can add more CO2 to the atmosphere and contribute to further warming.
The researchers say incorporating this newly identified process into climate models should improve predictions of future climate change and provide a more complete picture of how the global carbon cycle will respond to rising temperatures.
