Wetlands are a potent source of the radiatively important gas methane (CH₄). Recent findings have demonstrated that sulfate (SO₄ ²⁻) deposition via acid rain suppresses CH₄ emissions by stimulating competitive exclusion of methanogens by sulfate-reducing microbial populations. Here we report data from a field experiment showing that a finite pulse of simulated acid rain SO₄ ²⁻ deposition, as would be expected from a large Icelandic volcanic eruption, continues to suppress CH₄ emissions from wetlands long after the pollution event has ceased. Our analysis of the stoichiometries suggests that 5 years is a minimum CH₄ emission recovery period, with 10 years being a reasonable upper limit. Our findings highlight the long-term impact of acid rain on biospheric output of CH₄ which, for discrete polluting events such as volcanic eruptions, outlives the relatively short-term SO₄ ²⁻ aerosol radiative cooling effect.