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|Title:||Climatic Impact of Land Use in LCA - Carbon Transfers between Vegetation/Soil and Air|
|Authors:||MUELLER-WENK Ruedi; BRANDAO MIGUEL|
|Citation:||INTERNATIONAL JOURNAL OF LIFE CYCLE ASSESSMENT vol. 15 no. 2 p. 172-182|
|Type:||Articles in Journals|
|Abstract:||Background, aim, and scope Human use of land areas leads to impacts on nature in several ways. Within the framework of the UNEP-SETAC Life-Cycle Initiative, it was stated that LCA of land use should assess at least the impact on biodiversity, the impact on biotic production and the impact on the regulating functions of the natural environment. This study focuses on the climatic impact of land use, as determined by the CO2 transfers between vegetation/soil and the atmosphere in the course of terrestrial release and re-storage of carbon. Materials and methods Compared with the potential natural vegetation as a baseline, areas getting transformed by man (land transformations) as well as areas forced to maintain their existing non-natural state (land occupa-tions) may store reduced amounts of carbon in soil and vegetation, whereby the mobilized carbon is essentially transferred to the atmosphere in form of CO2, contributing to global warming. The size of this climatic impact is determined by the amount of carbon transferred per hectare, as well as by the duration of the carbon's stay in air. Generally, we consider this duration as limited by spontaneous reversal of vegetation and soil towards a more natural form as soon as human land use ends. Taking the mean stay in air of 1 ton carbon from fossil fuel com-bustion as a basis of comparison, 1 ton carbon released by e.g. a forest-to-cropland transformation can be ade-quately weighted by considering the timing of carbon backflow from air to the spontaneously re-growing forest. Results Carbon transfers to the air per hectare, as well as durations of carbon stay in air, are made available for the most important types of land transformation and land occupation, for locations in each of the terrestrial bi-omes of tropical forest, temperate forest, boreal forest, tropical grassland and temperate grassland. The carbon quantities are expressed as 'fossil-combustion-equivalent' tons of carbon so that they can be summed up with carbon amounts from fossil fuel combustion into the usual indicator for global warming potential. Discussion The results confirm that on a per hectare basis, transforming forests into cropland has a more serious climatic effect than continuing to occupy land as cropland for one additional year. But on a global basis, main-taining current cropland areas for one additional year is a serious driver of global warming, exceeding by far the contribution of the current annual rate of forest-to-cropland transformations. Further, forest-to-cropland trans-formations cause roughly similar carbon transfers to air per hectare in tropical, temperate or boreal zones, but due to slow forest restoration, transformation of boreal forests has a stronger influence on global warming. Conclusions and recommendations With the results of this study, impact assessment of land use with respect to global warming is feasible for LCA practice worldwide. Together with the two separate studies covering the impacts of land use on biodiversity and on biotic production, a tool will be available for a reasonably complete assessment of land use at global level.|
|JRC Institute:||Institute for Environment and Sustainability|
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