Newly analyzed data from researchers at Oxford challenges the long-held idea that natural rock weathering acts as a simple carbon sink. Instead, the Earth’s crust is also a source of carbon dioxide, releasing a level of greenhouse gas comparable to all the volcanoes on the planet. The findings appear in a respected scientific journal and are changing how scientists think about the carbon cycle.
Rocks hold carbon from ancient plant and animal matter that dates back millions of years. In addition, certain minerals can convert carbon dioxide from the atmosphere into solid minerals when rainwater, mildly acidic, interacts with them. This dual role — both storage and release — complicates the picture of how carbon moves through Earth systems.
For the first time, researchers quantified the natural release of CO2 from rocks entering the atmosphere, a process that has often been ignored in standard natural carbon cycle models. The team measured how carbon stored deep underground is liberated as rocks are uplifted from the sea floor to land, where oxidation drives carbon back into the air as CO2.
The study explains that, during the formation of mountains, rocks rich in ancient carbon release CO2 as they undergo chemical reactions with oxygen. This upward flow of gas is part of the same cycle that shaped major mountain ranges and influenced regional climates for eons. Measuring emissions from organic carbon within rock through geology has historically been difficult. To overcome this, researchers used a trace element released when organic carbon reacts with oxygen, providing a way to track the signal of rock-derived CO2 in water bodies that carry it away from the source.
Where this release is most pronounced appears to align with major orogenic belts that host some of the world’s most dramatic landscapes. Notable hotspots include the Himalayas, the Rocky Mountains, and the Andes. On a global scale, estimates show that weathering of rock organic carbon contributes around 68 megatons of carbon per year to the atmosphere. While this amount is small compared with human emissions from burning fossil fuels, it is still a meaningful piece of the planetary carbon ledger and mirrors the scale of volcanic CO2 fluxes in a given year.
Commenting on the significance, a senior scientist from the Earth sciences community notes that, although this rock-derived CO2 is far smaller than the vast human contribution, it represents a substantial natural flux that needs to be accounted for when modeling long-term carbon cycles and climate interactions. The realization that rocks can act as both a reservoir and a source of CO2 underscores the complexity of Earth system science and helps explain part of the variability seen in atmospheric carbon over geological time scales.
From an ecological and policy perspective, the new findings also touch on strategies for carbon management. While planting trees is often promoted as a quick fix for offsetting emissions, experts warn that this approach alone may be insufficient or misapplied if it does not consider ecological balance and biodiversity. The broader lesson is that carbon management requires a nuanced approach that respects natural processes, recognizes different sources and sinks, and avoids overreliance on a single strategy. The study’s insights emphasize the need for integrated climate policies that balance human emissions with a sophisticated understanding of natural carbon dynamics and their regional expressions across the globe.