Scientific shortcomings in environmental impact statements internationally

Abstract Governments around the world rely on environmental impact assessment (EIA) to understand the environmental risks of proposed developments. To examine the basis for these appraisals, we examine the output of EIA processes in jurisdictions within seven countries, focusing on scope (spatial and temporal), mitigation actions and whether impacts were identified as ‘significant’. We find that the number of impacts characterized as significant is generally low. While this finding may indicate that EIA is successful at promoting environmentally sustainable development, it may also indicate that the methods used to assess impact are biased against findings of significance. To explore the methods used, we investigate the EIA process leading to significance determination. We find that EIA reports could be more transparent with regard to the spatial scale they use to assess impacts to wildlife. We also find that few reports on mining projects consider temporal scales that are precautionary with regard to the effects of mines on water resources. Across our sample of reports, we find that few EIAs meaningfully consider the different ways that cumulative impacts can interact. Across countries, we find that proposed mitigation measures are often characterized as effective without transparent justification, and sometimes are described in ways that render the mitigation measure proposal ambiguous. Across the reports in our sample, professional judgement is overwhelmingly the determinant of impact significance, with little transparency around the reasoning process involved or input by stakeholders. We argue that the credibility and accuracy of the EIA process could be improved by adopting more rigorous assessment methodologies and empowering regulators to enforce their use. A free Plain Language Summary can be found within the Supporting Information of this article.