Halving of the northern wetland CH₄ source by a large Icelandic volcanic eruption

Northern temperate and high-latitude wetlands are a major source of the greenhouse gas methane (CH₄). Here, we estimate the sensitivity in the strength of this source to the effects of large Icelandic volcanic eruptions such as the Laki eruption of 1783-1784. We applied spatially explicit modeled sulfate aerosol and S deposition fields from a Laki eruption simulation to a climate-sensitive model of CH₄ emissions from wetlands. We estimate that the combined influence on climate and S deposition from the Laki eruption halved the output of CH₄ from wetlands north of 30°N for the first 12 months following the eruption. The largest short-term component responsible for the CH₄ suppression is the aerosol-influenced surface cooling, although the effect of large-scale S deposition on CH₄ emissions provides a longer-term suppressive effect on emissions. Together, we estimate this combination of processes to result in an annual suppression of ∼20 Tg CH₄ in the year of the eruption and two subsequent years. Further, the impact of the eruption on atmospheric CH₄ concentration extends beyond the likely duration of suppressed emission. The modeled effect of this large Icelandic eruption is consistent with ice core records of atmospheric CH₄ concentrations at the time and is equivalent, in size, to the current estimated suppressive effect of industrially derived S pollution on the global wetland CH₄ source.