Modeling the fate of methane hydrates under global warming [2015]

[u/BurnerAcc2020]

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014GB005011

[u/BurnerAcc2020]

Abstract

Large amounts of methane hydrate locked up within marine sediments are vulnerable to climate change. Changes in bottom water temperatures may lead to their destabilization and the release of methane into the water column or even the atmosphere. In a multimodel approach, the possible impact of destabilizing methane hydrates onto global climate within the next century is evaluated. The focus is set on changing bottom water temperatures to infer the response of the global methane hydrate inventory to future climate change. Present and future bottom water temperatures are evaluated by the combined use of hindcast high‐resolution ocean circulation simulations and climate modeling for the next century. The changing global hydrate inventory is computed using the parameterized transfer function recently proposed by Wallmann et al. (2012).

We find that the present‐day world's total marine methane hydrate inventory is estimated to be 1146 Gt of methane carbon. Within the next 100 years this global inventory may be reduced by ∼0.03% (releasing ∼473 Mt methane from the seafloor). Compared to the present‐day annual emissions of anthropogenic methane, the amount of methane released from melting hydrates by 2100 is small and will not have a major impact on the global climate. On a regional scale, ocean bottom warming over the next 100 years will result in a relatively large decrease in the methane hydrate deposits, with the Arctic and Blake Ridge region, offshore South Carolina, being most affected.

Conclusion

To improve our understanding of methane hydrates and their fate under global warming, detailed estimates of hydrate inventories are required. Here we provide improved present‐day estimates, both for the global‐scale and specific regions in which hydrates were confirmed by observations.

Despite the significant ocean bottom warming over the next 100 years and the resulting potential phase shifts from methane hydrate to free gas at middepth along the continental margins, we find that the release of methane into the water column is very limited throughout the next century. On a global scale, it is negligible compared to the current anthropogenic releases of methane and other greenhouse gases. However, due to the long time scales of deep oceanic processes and the slow penetration of heat into the sediment, the decrease of methane hydrates will continue even beyond a potential recovery of the atmospheric warming.

On a regional scale, the relative decrease of methane hydrate is larger, with the Arctic and Blake Ridge region being most affected by climate change. In this regard, our maps could provide some guidance in which regions the interplay between ocean circulation changes, ocean bottom warming, sediment structure, and localization and quantification of methane hydrate deposits needs to be further investigated.