Ancient carbon that was thought to be "sealed" has now returned to the atmosphere, not only surprising the scientific community, but also opening up a completely new perspective on the global carbon cycle, the foundation for humans to understand and control climate change - Photo: University of Bristol
In a global study led by the University of Bristol (UK) and published in the journal Nature , scientists have confirmed that a significant portion of the CO₂ released from rivers is not actually from fallen leaves or modern plant waste, but from ancient carbon stores deep in soil and rock.
Half of emissions come from ancient carbon
"The results were absolutely stunning. We previously thought that ancient carbon was 'locked away' in the ground for thousands of years. But it's now clear that a huge amount of ancient carbon is quietly returning to the atmosphere, much more than the models predicted," said Dr Josh Dean, a biogeochemist at the University of Bristol and lead author of the study.
The prevailing theory is that rivers act as carbon “transit stations,” transporting greenhouse gases from modern plant decomposition. But the team collected data from more than 700 river sections in 26 countries, measuring and analyzing the carbon-14 content to determine the “age” of the carbon.
The results showed that about 60% of the CO₂ and methane released from the river was ancient carbon, meaning it had been in the ground for hundreds to millions of years. The rest was “young” carbon, derived from vegetation that had decomposed within the last few decades.
"We have clearly established that half of the emissions come from ancient carbon, particularly carbon in deep soils and from the weathering of ancient rocks," said Professor Bob Hilton (University of Oxford), co-author of the study.
"Trees are working harder than ever"
Are these emissions a concern? The answer is yes. Very concerning.
Dr Gemma Coxon, a hydrologist at the University of Bristol, said: "Global rivers emit around 2 gigatonnes of carbon a year. Compared to human emissions (10-15 gigatonnes/year), this seems small. But the important thing is that most of it comes from carbon stores that we have long believed to be stable and not emitting."
This means that current climate models may be underestimating the true role and impact of rivers on atmospheric CO₂.
One positive from this study, however, is that plants and surface soils may be absorbing about 1 gigaton of CO₂ each year to compensate for the ancient carbon that is quietly leaking from deep soils and ancient rocks.
“We don’t yet know how human activities, such as land clearing, damming or deforestation, are affecting this ancient carbon flow. But it’s clear that trees and soils are working harder than ever to keep the climate system stable,” said Dr Josh Dean.
This finding further reinforces the importance of protecting forests, soils and natural vegetation, as the “last line of defence” that helps retain significant amounts of carbon, preventing it from being released into the atmosphere.
The study is just the beginning. Scientists plan to continue surveying more rivers in undocumented areas and study whether this ancient carbon flow is changing over time, especially as the planet warms and permafrost thaws.
The discovery that ancient carbon is "reviving" and escaping into the atmosphere could become one of the key factors helping us better understand climate change, something that seems so familiar but turns out to still have many unsolved mysteries.
And that reminds us once again: every river, every forest, every handful of soil... is part of the fight against climate change across the planet.
Source: https://tuoitre.vn/phat-hien-carbon-co-dai-dang-song-day-ro-ri-vao-khi-quyen-20250807211343962.htm
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