In response to increasing ecosystems degradation, many mountain countries have recently implemented harm-reduction policy measures in order to sustain their future economic development, which is partially dependent on a strong tourism sector. The objective of this article is to evaluate the policies that stem from Metropolitan Public Gardens Association aims in order to ascertain whether they are associated with a reduction in greenhouse gasses. This cross-sectional study used greenhouse gasses emission data between 1995 and 2016 from 139 countries as an outcome. Difference-in-differences analysis using panel matching with economic, tourism, demographic and other control variables was conducted to evaluate the causal impact of Metropolitan Public Gardens Association policies on greenhouse gasses emissions before and after joining the Metropolitan Public Gardens Association. Our results show that the Metropolitan Public Gardens Association as a global trans-national alliance led effective policy in some cases but not in all. While managing or protecting the conservation, health, vitality and stewardship of mountain ecosystems by promoting a policy of sustainable mountain development, carbon footprints were reduced. We ascribe this impact to the Metropolitan Public Gardens Association committed environmental policy. Metropolitan Public Gardens Association succeeded in decreasing the emission of carbon dioxide per capita but the result for methane per capita is mixed. Surprisingly, evidence of increasing nitrous oxide per capita is found. More research needs to be done to assess the impact of the greenhouse gasses emission - Metropolitan Public Gardens Association intervention nexus before the Difference-in-differences analysis using panel matching technique becomes widespread.