A recent study from Oxford University in the United Kingdom challenges the long-standing view that natural rock erosion acts solely as a climate sink for carbon dioxide. Instead, the research shows that CO2 can be released by rocks reaching the atmosphere through erosion and uplift, becoming a meaningful source of emissions that can rival volcanic output. The findings were reported in Nature and could influence how climate change is modeled and managed.
Rocks contain vast stores of carbon derived from ancient plant and animal matter that lived millions of years ago. This carbon forms part of what scientists call the geological carbon cycle, a planetary thermostat that helps regulate the Earth’s temperature over deep time.
During chemical weathering, rainwater carries acid that reacts with minerals in rocks, absorbing CO2 from the atmosphere. This process helps offset emissions from volcanic activity and is an integral piece of the Earth’s natural carbon cycle. In turn, the cycle contributes to a stable surface environment capable of supporting life for billions of years.
New evidence shows that rock-derived CO2 release into the atmosphere is a natural process
For the first time, researchers document that CO2 can be released from rocks during erosion as part of normal geological processes. The work indicates that emissions from this rock-derived CO2 are comparable in scale to volcanic emissions across the globe. Given its novelty, many climate and carbon-cycle models have not yet integrated this pathway.
Rocks that emit gas instead of trapping it
The mechanism unfolds when ancient seabed rocks, formed when organisms were buried in sediments, are brought to the surface by tectonic forces that raise mountains. In exposed settings such as the Himalayas or the Andes, organic carbon in these rocks meets air and water, triggering reactions that release CO2. The result is that eroded rocks can contribute to atmospheric CO2 rather than merely sequester it.
Measuring this CO2 release from rocks composed of organic carbon has been a challenge. In the new study, researchers used a trace element released when organic carbon reacts with oxygen to track the process. Sampling river waters to gauge these traces offers a way to quantify emissions, though projecting a global estimate would require extensive, perhaps impractical, data from rivers worldwide.
To translate these findings to a planetary scale, the researchers pursued two tasks. First, they assessed how much organic carbon remains near the surface in rocks. Second, they identified regions most susceptible to erosion, with emphasis on high-elevation, steep terrains where sedimentary rocks are exposed.
Led by a senior researcher from the Department of Earth Sciences, the team faced a central challenge: combining global maps with river data while accounting for uncertainties. They transferred the data to a high-performance computing system to simulate the complex interactions among physical, chemical, and hydrological processes. The result is a robust estimate of the total CO2 released as rocks erode and reveal ancient carbon to the atmosphere.
These rock-derived CO2 flows are comparable to the amounts released when silicate minerals weather under natural conditions. The research highlights large areas where weathering acts as a source of CO2, prompting a reconsideration of how weathering influences the carbon cycle.
Massive mountain ranges as CO2 sources
The analysis identifies key emissions hot spots among tall mountain belts that expose sedimentary rocks. Regions including the Eastern Himalayas, the Rocky Mountains, and the Andes emerge as significant sources. The global emission estimate from the erosion of organic carbon in rocks lands around several dozen megatons of carbon per year.
In commentary, the project’s lead scientist notes that the scale of rock-derived CO2 is about one hundredth of current human CO2 emissions from fossil fuel burning, and is similar in magnitude to volcanic fluxes. This finding positions rock erosion as a meaningful component of the Earth’s natural carbon cycle, rather than a passive process.
The researchers acknowledge that these fluxes may have varied across Earth history, particularly during periods when mountain building exposed large stocks of organic matter. They also anticipate that ongoing climate warming could enhance rock weathering and related emissions as mineral surfaces become more reactive.
Questions remain about how rock-derived CO2 emissions might evolve over the next century. While the team can produce robust global forecasts, they caution that precise changes require further study.
Reference work: Nature 2023 study documenting these revelations.
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Endnotes and data notes follow the study with a focus on secure, reproducible research practices.