Tuesday, June 10, 2014

New paper finds tropical lands are a net source of CO2 to the atmosphere

A new paper published in Global Change Biology finds "that tropical lands are on average a small carbon [dioxide] source to the atmosphere," attributed to deforestation, degradation, harvesting and peat fires [rather than the use of fossil fuels]. The CO2 from these sources is found by the authors to be 2.5 times greater than that from use of fossil fuels in the tropics. 

The tropical lands were previously assumed to be a net CO2 sink instead of a source, but this new paper adds to many others published over the last 2 years overturning prior major assumptions of the global carbon cycle. 

Perturbations in the carbon budget of the tropics

John Grace et al

The carbon budget of the tropics has been perturbed as a result of human influences. Here, we attempt to construct a ‘bottom-up’ analysis of the biological components of the budget as they are affected by human activities. There are major uncertainties in the extent and carbon content of different vegetation types, the rates of land-use change and forest degradation, but recent developments in satellite remote sensing have gone far towards reducing these uncertainties. Stocks of carbon as biomass in tropical forests and woodlands add up to 271 ± 16 Pg with an even greater quantity of carbon as soil organic matter. Carbon loss from deforestation, degradation, harvesting and peat fires is estimated as 2.01 ± 1.1 Pg annum−1; while carbon gain from forest and woodland growth is 1.85 ± 0.09 Pg annum−1. We conclude that tropical lands are on average a small carbon source to the atmosphere, a result that is consistent with the ‘top-down’ result from measurements in the atmosphere. If they were to be conserved, they would be a substantial carbon sink. Release of carbon as carbon dioxide from fossil fuel burning in the tropics is 0.74 Pg annum−1 or 0.57 MgC person−1 annum−1, much lower than the corresponding figures from developed regions of the world.

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