To validate our implementation, we compared Earthster’s results against the EXIOBASE-ImpactWorld+ (IW+) benchmark. The EXIOBASE-ImpactWorld+ benchmark contains the official ImpactWorld+ characterization factors adjusted for EXIOBASE exchanges. The table below shows the relative difference between Earthster and EXIOBASE-ImpactWorld+.
Legend: Values represent the relative difference as a percentage (0% = identical results; 100% = maximum difference).
Indicator | Mean difference (%) | Median difference (%) | Maximum difference (%) |
Mineral resources use | 11.2 | 5.1 | 100 |
Fossil and nuclear energy use | 7.7 | 6.4 | 100 |
Climate change, long term | 0 | 0 | 0.2 |
Climate change, short term | 0 | 0 | 0.2 |
Terrestrial acidification | 0 | 0 | 0 |
Marine eutrophication | 0 | 0 | 0 |
Freshwater acidification | 0 | 0 | 0 |
Freshwater eutrophication | 0 | 0 | 0 |
Particulate matter formation | 0 | 0 | 0 |
Human toxicity non-cancer | 0 | 0 | 0 |
Human toxicity cancer | 0 | 0 | 0 |
Water scarcity | 0 | 0 | 0 |
Photochemical ozone formation | 0 | 0 | 0 |
Ionizing radiations | 0 | 0 | 0 |
Land transformation, biodiversity | 0 | 0 | 0 |
Ozone layer depletion | 0 | 0 | 0 |
Analysis of Divergences
While the majority of categories show a near-perfect match (<1% difference), Earthster intentionally differs from the benchmarks in the Fossil and nuclear use and Mineral resources use categories.
1. Fossil Fuel Energy Content
The 7.7% average divergence in Fossil Energy Use is driven by differing assumptions regarding the energetic content of raw fuels. The reference benchmark utilizes values that appear to be at the lower range of physical likelihood for several key resources.
Benchmark Values: The benchmark assigns 19.1 MJ/kg to bituminous and anthracite coal. This is significantly lower than the standard minimum thresholds usually observed for these fuel types in global energy reporting.
Earthster Approach: We utilize Higher Heating Values (HHV) that reflect more typical industrial ranges (e.g., 32.6 MJ/kg for anthracite). This prevents a systematic underestimation of the total energy extraction in the model.
Natural Gas Liquids (NGL): Additionally, Earthster characterizes NGLs, which are currently omitted in the reference benchmark results.
2. Mineral Mass-Balance Corrections
The 11.2% divergence (with a 100% maximum) is due to a significant "Ore vs. Metal" discrepancy in the reference benchmark’s logic.
Over Characterization in Benchmark: For Uranium and Platinum Group Metals (PGMs), the benchmark erroneously applies pure-metal characterization factors to the total weight of the gross ore. This inflates the impact of these minerals by several orders of magnitude.
Earthster’s Physical Realism: We apply global average concentration factors to map only the actual metal content within the ore. This ensures that the resource scarcity results reflect the physical depletion of the metal rather than the weight of the surrounding rock.
Completeness: The benchmark omits Chromium, Manganese, and Fertilizer minerals n.e.c. Earthster includes these (using a Phosphate proxy for fertilizers) to ensure a complete representation of global material flows.