A systematic review of benefits to health from exposure to natural environments reported that significantly lower negative emotions, such as anger and sadness, were experienced after exposure to a natural environment in comparison with a more synthetic environment in a subset of studies where these were measured (Fig. S3.2; Bowler et al. 2010). But as this work is new, with limited generalised findings on the relationships between nature and mental health, we note this as a knowledge gap and do not assess progress to this target (Fig. 3.13).