Abstract
Abstract. The effect of Land Use Change and Forestry (LUCF) on terrestrial carbon fluxes can be regarded as a carbon credit or debit under the UNFCCC, but scientific uncertainty in the estimates for LUCF remains large. Here, we assess the LUCF estimates by examining a variety of models of different types with different land cover change maps in the 1990s. Annual carbon pools and their changes are separated into different components for separate geographical regions, while annual land cover change areas and carbon fluxes are disaggregated into different LUCF activities and the biospheric response due to CO2 fertilization and climate change. We developed a consolidated estimate of the terrestrial carbon fluxes that combines book-keeping models with process-based biogeochemical models and inventory estimates and yields an estimate of the global terrestrial carbon flux that is within the uncertainty range developed in the IPCC 4th Assessment Report. We examined the USA and Brazil as case studies in order to assess the cause of differences from the UNFCCC reported carbon fluxes. Major differences in the litter and soil organic matter components are found for the USA. Differences in Brazil result from assumptions about the LUC for agricultural purposes. The effects of CO2 fertilization and climate change also vary significantly in Brazil. Our consolidated estimate shows that the small sink in Latin America is within the uncertainty range from inverse models, but that the sink in the USA is significantly smaller than the inverse models estimates. Because there are different sources of errors at the country level, there is no easy reconciliation of different estimates of carbon fluxes at the global level. Clearly, further work is required to develop data sets for historical land cover change areas and models of biogeochemical changes for an accurate representation of carbon uptake or emissions due to LUC.
Highlights
Changes in the carbon pools for the terrestrial biosphere result in the uptake or release of carbon dioxide (CO2) from the atmosphere and shape climate change for the century
The terrestrial flux can be split into that part attributable to Land Use, Land Use Change and Forestry (LULUCF) and a residual component that accounts for other environmental changes (ENV)
The residual terrestrial flux can be associated with a wide range of environmental changes which include climate change, disease outbreaks, added nutrients (CO2 and nitrates), pollution damage (O3), and re-growth of vegetation in natural land that is not included under the United Nations Framework Convention on Climate Change (UNFCCC) reporting guidelines for LULUCF
Summary
Changes in the carbon pools for the terrestrial biosphere result in the uptake or release of carbon dioxide (CO2) from the atmosphere and shape climate change for the century. The terrestrial flux can be split into that part attributable to Land Use, Land Use Change and Forestry (LULUCF) and a residual component that accounts for other environmental changes (ENV). These LULUCF fluxes are mainly attributable to human activities and are reported for managed lands under the United Nations Framework Convention on Climate Change (UNFCCC) reporting guidelines, Published by Copernicus Publications on behalf of the European Geosciences Union. The Intergovernmental Panel on Climate Change (IPCC) and Food and Agriculture Organization (FAO) definitions and methodologies differ slightly as discussed in the IPCC Special Report on LULUCF (IPCC, 2000) In many cases these ENV fluxes may be indirectly attributed to human activities. As seen from the uncertainties above, it is difficult to separate LUCF and ENV emissions (House et al, 2003), much less to attribute national ENV fluxes
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