The carbon cycle reveals its secrets


Today, thanks to the work of Kristof Van Oost’s team at the UCL Earth and Life Institute, we have a better understanding of the carbon cycle. Specifically, they have discovered a process that offsets carbon emissions caused by deforestation.

When a forest is cut down, the carbon in the biomass and soil is immediately released into the atmosphere in the form of CO2, a greenhouse gas that contributes to global warming. Understanding this process is essential. ‘Since the dawn of agriculture,’ explains the UCL Earth and Life Institute’s Kristof Van Oost, ‘countless forests have been cut down and huge quantities of carbon released into the atmosphere. But this has always been difficult to quantify.’

An original approach

To gain a better understanding, he and his colleague Zhengang Wang focused not on deforestation but on the erosion that follows it. ‘When trees are cut down,’ Dr Van Oost says, ‘the land is subjected to severe erosion that lasts several years and leads to the formation of sediment in lakes, oceans, ice, and alluvial plains. We wanted to study this sediment’s impact on the carbon cycle.’ They carried out an extensive study of sediment core samples taken from all over the world in areas with different climates during the Holocene .

                  cycle carbone - Kristof Van oostcycle carbone - Kristof Van oost

Carbon trapped in sediment

This approach allowed them to study thousands of soil profiles over a period of 8,000 years and to make an astonishing discovery: ‘We noticed that carbon emitted rapidly into the atmosphere after deforestation didn’t stay there indefinitely: 30 to 40% was reabsorbed by the ground, then trapped and stored by sediment. Rapid carbon emission caused by deforestation is thus followed by a slower process of post-erosion sediment reabsorbing this same carbon. It’s a very valuable discovery that shows we overestimated the impact of deforestation.’

Two opposing theories reconciled?

In addition to adding to our knowledge of the carbon cycle, the study, published in the journal Nature Climate Change, reconciled two theories concerning the impact of deforestation on the quantity of carbon in the atmosphere during the Holocene.

To date, two schools of thought have developed: the first holds that the impact was very great since the beginning of the Holocene, because that is when agriculture began; the second cites the low quantity of carbon isotope traces associated with this period in glacier core samples as an indication that the impact was weak and only became greater with the onset of the Industrial Revolution. Dr Van Oost concludes, ‘Our work shows that these traces represent only half the quantity of deforestation carbon emissions. The human impact was great during both the beginning of the Holocene and the Industrial Revolution.’


Elise Dubuisson


A glance at Kristof Van Oost's bio

kristof van oost

2003                  PhD, Sciences, KU Leuven

2004-2006        EU Marie Curie Fellow, Earth System Science Group, University of Exeter, UK

2006-2007        Postdoctorate, FWOVlaanderen

2007-2015        FNRS Research Associate, Earth and Life Institute, TECLIM, UCL

Since 2016       FNRS Senior Research Associate, Georges Lemaître Centre for Earth and Climate Research, Earth and Life Institute, UCL

Published on April 11, 2017