There are many examples where green infrastructure offers much better value for public investment than the alternative, for example natural water filtration and natural flood defence.
Alan Spedding over at RuSource had identified and summarized an important report with the less-than-exciting title "Natural England Research Report NERR033 ‘Microeconomic Evidence for the Benefits of Investment in the Environment – review’.
Natural climate control is much cheaper than the air-conditioning (or heating) it replaces. Natural air filtering is likely to be efficient compared to technical alternatives, particularly as trees provide so many other benefits. Access to greenspace and the promotion of active travel are extremely cost-effective ways to address Mental and physical ill-health.
From RuSource and Natural England