What is IMPACT World+ ?
Most of the impacts modelled in LCIA are regional or local. However, LCIA methodologies currently offer generic characterization factors (CFs) representing average conditions for a specific area (country or continent) that do not account for the spatial variability of impacts.
IMPACT World+ was developed in response to the need of regionalized impact assessment covering the whole world, implementing state-of-the art characterization modelling approaches developed as a joint major update to IMPACT 2002+, EDIP, and LUCAS. It includes uncertainty information encompassing both spatial variability and model uncertainty. It provides factors for each continent and allows to regionally assess any geo-referenced emission/resource use, such as provided by ecoinvent 3.0, and to determine the uncertainty related to an unknown emission location by associating the corresponding geographical variability of each CF at a given geographical scale.
This LCIA methodology has been developing by a group of leading LCIA expert and researchers* with the support of their respective teams.
Features of IMPACT World+
Regionalization, uncertainties and geographical variability
We have developed characterization models for local and regional impact categories, each of them based on an appropriate spatial scale. The latter is defined around the most sensitive and spatially variable modeling parameters, such as watersheds for water use impacts, biomes for land use impacts, or based on an archetype approach for example urban/rural archetypes for respiratory impacts (the most sensitive parameter being population density) or soil and water archetypes for metal toxic impacts (the most sensitive parameters being some soil/water properties such as pH etc.).
Particular attention has been given to the harmonization of modelling assumptions between different impact pathways. The uncertainty associated with the CFs for each of these “fine scale” models has been estimated. These fine scale CFs have subsequently been aggregated at the country, subcontinental, and global scales using the likely geographical distribution of emissions (or emission proxis) as weighting factors. This resulted in CFs at different geographical resolutions, each with its own associated uncertainty and spatial variability. Regionalized CFs were calculated for the following impact categories: respiratory effects, human and ecosystem toxic impacts, ionizing radiations, water use, acidification, eutrophication and land use. For these impact categories, characterization factors are available at the following spatial scales:
- global default,
- continental (nine regions),
- fine resolution (e.g. sub-watershed or ecoregion), that vary depending of the impact category going from biome scales down to 0.5 x 0.5 degrees grid scale).
Each generated CF (regionalized or not) has its own associated uncertainty and spatial variability, the latter depending on the scale and thus decreasing with increasing spatial resolution.
The global framework adopted is presented in Figure 1. The novelties introduced in IMPACT World+ are numerous:
- USEtox model for toxic impacts is included for the first time in a comprehensive LCIA method with continent-specific factors and consistent spatialized alternatives
- Water use impacts are also included for the first time in a comprehensive LCIA method with continent-specific factors and consistent spatialized alternatives
- Major modelling improvements have been developed for land use with the inclusion of ecosystem services, acidification with an improved modelling of the atmospheric fate, resource use with the introduction of an extraction-consumption-competition approach, respiratory effects with new epidemiologically derived factors, the inclusion of pesticide residues impacts, and finally, for eutrophication with a world model at 0.5 x 0.5 degrees.
- For a few categories, midpoint indicators could be further divided into midpoint subcategories: for example, the “human toxicity” category is composed of non carcinogen, carcinogen, respiratory inorganics and ionizing radiation on human health, while ecotoxicity is further subdivided into freshwater exotoxicity, marine ecotoxicity, terrestrial ecotoxicity, and ionizing radiation impacts on ecosystems.
- While midpoint indicators can be reported and interpreted separately, each midpoint impact is also modeled up to the three areas of protection, human health, ecosystem quality, and ecosystem services & resources, allowing their respective contribution to be put into perspective. The latter area of protection includes the impacts on human society with no direct consequences on health such as abiotic ressource use, as well as depreciation of ecosystem services.