Overestimating climate warming-induced methane gas escape from the seafloor by neglecting multiphase flow dynamics

Continental margins host large quantities of methane stored partly as hydrates in sediments. Release of methane through hydrate dissociation is implicated as a possible feedback mechanism to climate change. Large-scale estimates of future warming-induced methane release are commonly based on a hydrate stability approach that omits dynamic processes. Here we use the multiphase flow model TOUGH+hydrate (T+H) to quantitatively investigate how dynamic processes affect dissociation rates and methane release. The simulations involve shallow, 20-100m thick hydrate deposits, forced by a bottom water temperature increase of 0.03 degrees Cyr(-1) over 100years. We show that on a centennial time scale, the hydrate stability approach can overestimate gas escape quantities by orders of magnitude. Our results indicate a time lag of>40years between the onset of warming and gas escape, meaning that recent climate warming may soon be manifested as widespread gas seepages along the world's continental margins.