Soils are like giant carbon piggy banks, holding more than twice as much carbon as the air around us. But as the planet heats up, those piggy banks might start cracking open, letting carbon dioxide spill out and make climate change worse. A new study, shared on May 18, 2025, from the MARUM Center for Marine Environmental Sciences, shows that rising temperatures in tropical and subtropical regions could trigger a fast release of soil carbon, way more than scientists thought.

Digging into the Past

Instead of poking around in soil, Dr. Vera Meyer and her team got creative. They studied a sediment core from the Mediterranean seafloor near the Nile Delta, which acts like a time capsule of dirt washed down the Nile River from northeast Africa over 18,000 years. The Nile’s massive drainage area covers subtropical and tropical zones, picking up bits of soil carbon along the way. By looking at this core, the team could see how soil carbon changed since the last ice age.

“The Nile’s sediment tells us how old the carbon was when it got to the sea,” said Enno Schefuß from MARUM.

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Temperature, Not Rain, Is the Key

The big surprise? Rainfall and runoff didn’t change the age of soil carbon much. But temperature did. As the Earth warmed after the ice age, carbon in the Nile’s sediments got “younger,” meaning it was breaking down faster. Warm, humid conditions revved up microbes in the soil, which chowed down on organic matter and pumped out CO2. This breakdown was way stronger than what today’s climate models predict.

“Our models are missing the mark on how sensitive soil carbon is,” said Dr. Peter Köhler from AWI Bremerhaven.

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Why It’s a Big Deal

Soils aren’t just dirt—they’re climate players. In places like Africa’s tropics, where it’s warm and wet, microbes work overtime, turning soil carbon into CO2 quickly. The study shows this process is super sensitive to temperature spikes, which is bad news as the planet’s already warmed 1.2°C. If tropical soils keep heating up, they could flip from storing carbon to spitting it out, making it harder to hit climate goals like keeping warming below 1.5°C.

What’s Next?

The study, backed by MARUM’s “Ocean Floor” project, is just the start. The team wants to keep tracking how carbon moves from land to sea, especially in tropical zones where 50% of global soil carbon sits. Better models could help predict how much CO2 soils might add to the air by 2050, when warming could hit 2°C without action. For now, this research warns that ignoring soil carbon’s sensitivity could leave us blindsided by a faster-warming world.

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