Do Collective Actions Clear Common Air? The Effect of International Environmental Protocols on Sulphur Emissions

We consider the effects of voluntary international environmental protocols on emissions with regard to the 1985 Helsinki Protocol and the 1994 Oslo Protocol on the reduction of sulphur oxides. Our analysis utilizes panel data from 30 European countries for the period 1960–2002. We divide these countries into “participants” and “non-participants”, i.e., those that did and those that did not ratify the specific protocol. We use a difference-in-difference estimator that focuses on the difference in emissions before and after signing a specific protocol and compares it with this difference for non-participant countries. Difference-in-difference estimation methods rely on annual data and may induce serial correlations in the variables. We use randomly generated placebo protocols to test the estimated effects. In a panel data regression model, where we include country and year dummies, the effect of the Helsinki agreement in reducing sulphur emissions is around three per cent per year, and the effect of the Oslo agreement is around four per cent per year. Correcting the standard errors for serial correlation in both dependent and independent variables is important and overlooked in the previous empirical literature on the evaluation of international agreements.