  As the global economy continues to grow, ecosystem services tend to stagnate
or decline. Economic theory has shown how such shifts in relative scarcities
can be reflected in the appraisal of public projects and environmental-economic
accounting, but empirical evidence has been lacking to put the theory into
practice. To estimate the relative price change in ecosystem services that can
be used to make such adjustments, we perform a global meta-analysis of
environmental valuation studies to derive income elasticities of willingness to
pay (WTP) for ecosystem services as a proxy for the degree of limited
substitutability. Based on 861 income-WTP pairs, we estimate an income
elasticity of WTP of around 0.79 (95-CI: 0.60 to 0.97). Combining these results
with a global data set on shifts in the relative scarcity of ecosystem
services, we estimate relative price change of ecosystem services of around 2.2
percent per year. In an application to natural capital valuation of non-timber
forest ecosystem services by the World Bank, we show that their natural capital
value should be uplifted by more than 50 percent (95-CI: 32 to 78 percent),
materially elevating the role of public natural capital. We discuss
implications for relative price adjustments in policy appraisal and for
improving estimates of comprehensive national accounts.
