Reported evidence of greenness co-benefits on health, climate change mitigation, and adaptation: a systematic review of the literature

This systematic review aims to appraise the quality of evidence on greenness co-benefits of climate change and health. Although there is evidence of the co-benefits of greenness on climate change and health, the research is of poor quality when it comes to addressing the connections and identifying mediators of greenness and climate change mitigation associations. The evaluation sought to identify areas where there was little or no evidence to guide future research. Current published studies mainly cover six health outcome categories (birth outcomes, physical activity, mental wellbeing, obesity, mortality, and cognitive function). For adaptation, greenness and climate change, associated studies included (a) cooling down effects and urban heat island impacts, (b) air quality improvement, and (c) flood mitigation. For each outcome, we performed a systematic search of publications on Web of Science, PubMed, Google Scholar, and Science Direct databases from 2000 to July 2021. After retrieving records in which full papers were assessed and non-English articles were excluded, a total of 173 articles, including research articles and reviews, were chosen. To ascertain the strength of the evidence, all interventions were assessed using the GRADE approach. The quality of evidence ranged from moderate to high for most categories of health outcomes (birth outcomes, mental wellbeing, mortality). GRADE assessment provided low-quality evidence for studies on air quality, flood mitigation, physical activity, and obesity due to poor study design (observational or limited data) and high heterogeneity (some data provided variability), and the review concluded that there is insufficient evidence on firm recommendations for public health interventions. Due to a huge amount of low-quality evidence and several areas of overlapping study, this evaluation recognized the co-benefits of greenness on climate change and health as an understudied field and hence as a research gap. The evidentiary foundation for greenness-climate change mitigation links was generally weak. Future research on climate change greenness co-benefit interventions should pay special attention to flood prevention, air quality interactions, and health effects including physical activity and obesity.