We used to think rocks helped scrub carbon from the atmosphere, but they might be a big source of emissions instead!

When we think of climate change’s biggest culprits, most might imagine giant soot-riddled chimneys of smoke emanating from monotone factories. But a host of natural processes also contribute significantly to the warming phenomenon, such as natural release from volcanoes and, surprisingly enough, the weathering of rocks.

Rock weathering via the actions of water and wind is as natural as a phenomenon can get, with most experts regarding the process as a silent hero in healing and helping our planet. But a recent study found that this might also be a significant source of carbon dioxide emissions!

The previously held notion was that after precipitation, the rainwater — being a weak acid — would interact with certain rock minerals, dissolving carbon dioxide and removing it from the atmosphere. But there’s always more to things than meets the eye.

The Earth's crust is a dynamic landscape. As major and minor tectonic plates push against each other, many long-buried fragments of rocks emerge from the depths. This is how mountains like the Himalayas and the Andes continue to grow taller in size.

However, from the cold oceanic depths comes another long-forgotten foe. The tectonic upheaval pries to the surface corpses of ancient plants and animals, now in the form of carbon-rich rock sediments.

As these carbon sources weather and encounter water and air, oxygen mixes with the exposed carbon, creating the infamous carbon dioxide that we have all come to know and despise. The team found that the amount of carbon dioxide expelled into the atmosphere via this process is no joke either, rivalling the levels released by volcanoes around the world!

To calculate the full extent of such weathering processes worldwide however was a task. Scientists had to measure levels of rhenium, an element released into water when rock carbon interacts with oxygen, and use it to try to estimate how much carbon is released into the atmosphere by these sources.

After deciphering how much organic carbon is available in surface-level rocks and where erosion was most prevalent — such as tall mountains where water flows at fantastic speeds — they identified the resultant carbon source hotspots, which included the eastern Himalayas, the Rocky Mountains and the Andes.

All in all, models revealed that the process may be releasing about 68 megatons of carbon per year, around the weight of a pod of 450,000 blue whales. While this is still 100 times lesser than present day human CO2 emissions from fossil fuel burning (which just goes to show how extravagantly we use the resource), it is significant enough to be considered when calculating Earth's natural carbon cycles, scientists argue.

Moreover, this number could increase. As rocks face more warming at the hands of climate change, we could be looking at greater carbon leaks from such sources.

"While the carbon dioxide released from rock weathering is small compared to present-day human emissions, the improved understanding of these natural fluxes will help us better predict our carbon budget” explains Jesse Zondervan, the lead author of the study.

The findings of this research have been published in Nature and can be accessed here.

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