Development of a policy-based distance-to-target weighting method in life cycle impact assessment for Nigeria

Abstract Purpose Weighting in LCA is important as it supports decision-making by prioritising and determining which impact categories are more important. However, the lack of weighting factors in developing countries forces LCA practitioners to adopt weighting values developed for other countries, leading to a less transparent decision-making process. One transparent and easily reproducible distance-to-target (DtT) weighting method that can be applied in Nigeria is the Swiss-developed ecological scarcity method. This method is based on the ratio of the current environmental situation of a country, region or product to the desired policy targets. The purpose of this study was to apply the ESM to develop weighting factors and eco-factors for Nigeria. Methods The normalization and current flows data for emissions and resource use in 2010 (base year) were collected from official data sources, and the critical flows were extracted from corresponding policy targets of the Government of Nigeria in 2030 (target year). The ESM was then applied to the aggregated data to derive Nigeria-specific weighting factors and eco-factors as the quantitative indicators for the emissions and resources. Results and discussion Weighting and eco-factors for emissions and resources were developed for 25 environmental issues in Nigeria. NOx, total petroleum hydrocarbon and land use weigh heavily. Except for carcinogenic substances in the air, emissions to water resulted in high eco-factors: TPH, phenol, total nitrogen, nitrate, ammonia and heavy metals (human and ecotoxicity). Policymakers in Nigeria need to set quantitative emission reduction targets for substances and such as carcinogenic substances in the air, oil spills and metal mineral resources. Conclusions The ESM was used to develop Nigeria’s eco-factors as quantitative indicators for emissions or resource use using the normalization and current flows in 2010 obtained from government data sources as base year data. The critical flows were extracted from the policy targets of the government of Nigeria, with 2030 as the target year. The eco-factors can support environmental sustainability decision-making in Nigeria. Future methodological development should apply updated policy targets and more data to calculate eco-factors for missing substances such as waste (radioactive and non-radioactive), heavy metal emissions to air and soil, emissions to groundwater, photochemical ozone creation substances and phosphorous in surface water and soil.