Abstract
The terrestrial biosphere currently absorbs about 30% of anthropogenic CO2 emissions. This carbon uptake over land results primarily from vegetation’s response to increasing atmospheric CO2 but other factors also play a role. Here we show that since the 1930s increasing population densities and cropland area have decreased global area burned, consistent with the charcoal record and recent satellite-based observations. The associated reduced wildfire emissions from increase in cropland area do not enhance carbon uptake since natural vegetation that is spared burning was deforested anyway. However, reduction in fire CO2 emissions due to fire suppression and landscape fragmentation associated with increases in population density is calculated to enhance land carbon uptake by 0.13 Pg C yr−1, or ~19% of the global land carbon uptake (0.7 ± 0.6 Pg C yr−1), for the 1960–2009 period. These results identify reduction in global wildfire CO2 emissions as yet another mechanism that is currently enhancing carbon uptake over land.
Highlights
The terrestrial biosphere currently absorbs about 30% of anthropogenic CO2 emissions
It is well known that the atmospheric CO2 concentration ([CO2]) is rising in response to increasing anthropogenic fossil fuel emissions of CO2 and due to land use change (LUC) emissions associated with deforestation of natural vegetation, as a result of increases in cropland and pasture area
The caveat with reduced wildfire fire emissions due to LUC associated with increase in crop area is that this reduction does not enhance the land carbon sink
Summary
The terrestrial biosphere currently absorbs about 30% of anthropogenic CO2 emissions. For the period 2006–2015, only 45% of the 9.3 ± 0.5 Pg C yr−1 anthropogenic emissions are estimated[3] to stay in the atmosphere while the land (30%, 3.1 ± 0.9 Pg C yr−1) and ocean (25%, 2.6 ± 0.5 Pg C yr−1) took up the rest This positive global net flux of carbon from the atmosphere to the land, which indicates a carbon sink, is the result of the response of the terrestrial vegetation to multiple forcings[5,6]. These well-recognized forcings include an increase in [CO2], anthropogenic LUC and nitrogen deposition, and climate change associated with increasing [CO2] and other greenhouse gases (GHGs), as well as changes in the concentration of atmospheric aerosols. This net carbon uptake results in an increase in the carbon density of vegetation and/or soil carbon pools
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