A new study analysed the extent to which changing land-use practices, such as deforestation, can affect carbon emissions.

Role of terrestrial biosphere in counteracting climate change may have been underestimated

New research suggests the capacity of the terrestrial biosphere to absorb carbon dioxide (CO2) may have been underestimated in past calculations due to certain land-use changes not being fully taken into account.

It is widely known that the terrestrial biosphere (the collective term for all the world’s land vegetation, soil, etc) is an important factor in mitigating climate change, as it absorbs about 20% of all fossil fuel CO2 emissions.

But its role as a net carbon sink is affected by land-use changes such as deforestation and expanded agricultural practice.

A new study, conducted by an international team including scientists from the University of Exeter, has analysed the extent to which these changing land-use practices affect carbon emissions – allowing the levels of CO2 uptake by the terrestrial biosphere to be more accurately predicted.

The results, published in the journal Nature Geoscience, not only show that CO2 emissions from changing land-use practices are likely to be significantly higher than previously thought, but also imply that these emissions are compensated for by a higher rate of carbon uptake among terrestrial ecosystems.

Co-author Professor Stephen Sitch, from the University of Exeter, said: “The results imply that reforestation projects and efforts to avoid further deforestation are of the utmost importance in our pursuit to limit global warming to below 2oC, as stated in the Paris climate agreement.”

Co-author Professor Pierre Friedlingstein, from the University of Exeter said: "The terrestrial biosphere is the least constrained component of the global carbon cycle. It is often estimated as the residual from how much of our fossil fuel CO2 emissions remain in the atmosphere or are absorbed by the ocean. Also it's a source of carbon following deforestation but it's also a carbon sink as a response to atmospheric CO2 increase.

"This study is a bit of a good news/bad news story. Bad news first: It shows that land-use changes emissions are larger than previous estimates. God news is: this implies that the land carbon sink is also larger than assumed before."

Co-author Dr Tom Pugh, from the University of Birmingham, said: “Our work shows that the terrestrial biosphere might have greater potential than previously thought to mitigate climate change by sequestering carbon emissions from fossil fuels. However, to fully realise this potential we will have to ensure that the significant emissions resulting from land-use changes are reduced as much as possible.”

In addition to the researchers from the Universities of Birmingham and Exeter, this paper is co-authored by researchers affiliated with the following institutions: Department of Atmospheric Environmental Research (Germany), Max Planck Institute for Meteorology (Germany), Imperial College London (UK), ETH Zürich (Switzerland), LSCE (France), NASA Goddard Space Flight Center (US), Aix-Marseille Université (France), University of Maryland (US), German Federal Institute of Hydrology (Germany), The Institute of Applied Energy (Japan), Lund University (Sweden), Met Office Hadley Centre (UK), Max Planck Institute for Biogeochemistry (Germany).

Date: 30 January 2017

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