After nearly four decades of poking dirt in Massachusetts, scientists have discovered that forest soils are even worse at keeping carbon to themselves than previously thought. The world's longest-running soil warming experiment, led by Jerry Melillo of the Marine Biological Laboratory, kept plots in the Harvard Forest at a toasty 5 °C above ambient for 37 years. That temperature was chosen because it represented the upper range of global warming projections when the experiment began - back when scientists still believed in reasonable timelines.

Melillo explains that microbes, the unsung heroes of soil ecosystems, usually break down organic matter and recycle nutrients. But as warming reshapes microbial communities, they start eyeing the long-term carbon stores - the kind everyone assumed would stay put. During the fourth decade of the experiment, those stable carbon pools began decomposing, releasing extra CO₂ into the atmosphere. This suggests that forest soils may be a bigger carbon leak than models currently account for.

Global average temperatures have already risen by 1.1 - 1.4 °C since the Industrial Revolution, and future warming depends on how seriously we take emission reductions. "If we dramatically cut CO₂ emissions from fossil fuel burning, or reduce deforestation, the projected increase would be lower," Melillo notes, presumably while wondering if anyone is listening.

The newly observed breakdown of stable soil carbon points to a stronger climate feedback loop: warmer planet → more soil carbon released → more warming. Researchers say incorporating this into climate models should improve projections, which is good, because the current ones apparently needed more bad news. The study was provided by the Marine Biological Laboratory, and no, they did not warm the soil by arguing with it.