• Earth’s top 2 meters (6 feet) of soil hold 2.5 trillion metric tons of carbon — more than is held in living vegetation and the atmosphere combined. But soil carbon sinks are under threat — global warming could trigger a positive feedback loop that seriously accelerates soil emissions, just as we take steps to decarbonize society.
• The effects of elevated temperature and atmospheric CO₂ on soil carbon have been factored into climate models. But those models don’t currently capture the true complexity of the soil carbon sink, in part because scientists don’t fully understand the mechanisms that influence soil carbon gains and losses.
• Major knowledge gaps urgently need to be addressed: How are long-term soil carbon stores protected from microbial consumption (and CO₂ release)? And how will global warming alter microbial communities, deep soil carbon, and the climate sensitivity of tropical soils (which store a third of global soil carbon)?
• Improved understanding of soil carbon dynamics could offer an opportunity to better manage agricultural and forest soils for carbon sequestration. With proper management, degraded soils could sequester a billion tons of additional carbon annually, making them a key ally in the fight against climate change.

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