IMPACT World+ / a globally regionalized method for life cycle impact assessment

IMPACT World+ is a life cycle impact assessment methodology which characterizes thousands of substances spanning across many compartments and sub-compartments of the environment. It differentiates 45 impact categories, both at midpoint and damage levels.

For more information on IW+, refer to our website (https://www.impactworldplus.org/) and scientific article (https://doi.org/10.1007/s11367-019-01583-0).

New in 2.0

Why do we change to 2.0? IW+ has been completely restructured in its management to provide a more robust and transparent generation of the characterization factors. In the process, many inconsistencies from previous versions have now been resolved. More on these corrections below.

The different files

• impact_world_plus_2.0_dev.xlsx - The dev file is a file useful for developers and maintainers of databases/datasets who wish to link IW+ 2.0 to their databases/datasets.
• impact_world_plus_2.0_ecoinvent_v3x.xlsx - These Excel files match IW+ to "pure" ecoinvent (as in unaltered by various software) in an Excel table
• impact_world_plus_2.0_ecoinvent_v3x_as_df.xlsx - These Excel files match IW+ to "pure" ecoinvent (as in unaltered by various software) in a pandas.DataFrame format, directly readable in Python (pandas. read_excel())
• impact_world_plus_2.0_exiobase.xlsx - This file links IW+ to the Exiobase GMRIO database (https://doi.org/10.5281/zenodo.5589597). Once the file is read through pandas (pandas.read_excel()), the resulting matrix can directly be multiplied to the environmental extensions of exiobase (S, F or F_Y if using the pymrio package).
• impact_world_plus_2.0_openLCA.zip - This file links openLCA elementary flows to IW+. It can be directly downloaded in the openLCA software as a JSON-LD file.
• impact_world_plus_2.0_simapro.csv - This file links SimaPro elementary flows to IW+. It can be directly downloaded in the SimaPro software.
• impact_world_plus_2.0_source.accdb - This is the source file. This file is only useful for the IW+ internal team. It is provided for transparency, as well as for users who wish to generate all these files themselves through the open-access code of IW+.
• impact_world_plus_20_brightway2.f61be652158aa231066614610cddcbd5.bw2package - This file links brightway2 elementary flows to IW+. The current file works with the biosphere3 version corresponding to ecoinvent3.8. To import the file, you need to pass through brightway itself (it cannot be done through the activity-browser for now). The function to import a .bw2packge file is bw2.BW2Package.import_file().

Corrections between previous versions and 2.0

• Long term emissions and time dependent impact categories

In IW+, there are some damage categories which are split between short and long term impact: Climate change (both human health and ecosystem quality), freshwater ecotoxicity, human toxicity (both cancer and non cancer) and marine acidification. For these damage categories, the total impact is split between a short term impact category and a long term one. 100 years is the time horizon chosen to differentiate between short and long term impacts.

The timely resolved characterization factors have been harmonized to the timely resolved inventory : short term emissions (i.e., most emissions in LCA inventory databases) have a shorter term impact (corresponding to what is happening in the first 100 years after the emission) and a long term impact (corresponding to the residual impact after 100 years). Long term emissions reported in some LCA inventory databases (for example the emissions identified in ecoinvent with a sub-compartment with "long-term" in its name, such as: "low-population density, long-term") are considered as having 100% of their impact at long term, hence only have a long term CF.

Note that the additivity of short and long term impacts in IW+ is only relevant for damage indicators. The midpoint indicators Climate change, short and long term should not be added together.

• Toxicity and ecotoxicity - Metal emissions in groundwater

The impact of metal emissions in the groundwater compartment cannot presently be determined. It is a current limitation of the environmental impact models : there is no groundwater compartment in USEtox accounting for metal fate to surface water. Therefore, IW+ makes the assumption of fixing the characterization factor of metal emissions emitted directly to the groundwater sub-compartments to zero. It also ensures consistency with the modeling approach for other impact categories and emissions. Some metals do end up in the groundwater and may reach surface water and have toxic or ecotoxic impact, but we are currently unable to assess their impact.

• Marine eutrophication - air emissions

Some emissions to air and some sub-compartments were missing. They are now all characterized.

• Land occupation and transformation update

CF values for land occupation and transformation elementary flows were updated for the following land use: annual crops, permanent crops and agriculture (mosaic).

• Ionizing radiations

CF values for the midpoint indicator and the human health damage indicator have been updated. New values for the water compartment and the ocean sub-compartment were integrated. Also, new substances have been added: Americium-241, Strontium-90, Thorium-230.

• Acidification and eutrophication midpoint categories

Midpoint values for these categories were not properly normalized in some previously generated versions of IW+. Now they have been properly normalized so that, e.g., the CF for the emission of 1kg SO2, GLO is 1 kgSO2eq for acidification.

• Water impact categories new elementary flows

Characterization factors for many regionalized elementary flows for the categories: Water scarcity / Water availability, human health / Water availability, freshwater ecosystem / Water availability, terrestrial ecosystem, were added for new sub-regions covered in LCA databases such as CN-AH or IN-AP. The country level CF values have been used as a proxy to characterize  these new elementary flows (i.e., the CF for CN-AH is equal to the CF for CN).

• Precise report of changes

The precise report of changes (flow by flow) can be found here: https://github.com/CIRAIG/IWP_Reborn/tree/master/Report_changes

Generating the files

For those interested in generating the files themselves, or who need to go check under the hood what assumptions were made, the code to generate these files is available on Github (https://github.com/CIRAIG/IWP_Reborn). The only file needed to generate all the others is the source file ( impact_world_plus_2.0_source.accdb ) available in this release.

What's next?

In the coming year (2023), IW+ will start to integrate major updates to its characterization factors. These updates will first stem from updates of other impact assessment methods, for example, updates of the IPCC, which is used for Climate Change categories in IW+ or updates of ReCiPe which is used for Photochemical oxydant formation categories. They will also stem from updates of environmental indicators developed by research teams associated with the development of IMPACT World+ on water availability, ecotoxicity, mineral resource depletion and a new plastic environmental indicator.
New features regarding the Ecosystem services area of protection, the concept of Areas of concern, the integration of native regional characterization factors (at a much smaller scale than currently) in the different software or the integration of the CF uncertainty due to geographical aggregation in LCA software will also be integrated to the method in the future.