Book 2.indb - US Climate Change Science Program

Abrupt Climate ChangeThese recent studies highlight the fact that keyuncertainties remain in our understanding ofnatural methane emissions from wetlands andtheir susceptibility to climate change as wellas in our ability to predict future emissions.Among the most important uncertainties in ourunderstanding and required improvements toprocess-based models are (1) the contributionof ebullition and changes in ebullition to totalmethane emissions; (2) the rate of change inpermafrost distribution and active layer thicknessand associated changes in distribution ofwetlands and lakes as well as, more generally,terrestrial ecosystems; (3) model representationof soil thermal and hydrologic processesand their response to climate change; (4) thecontribution that shifts in vegetation andchanges in peatland functioning will have onthe methane cycle; and (5) representation of thehighly variable and regionally specific methaneproduction and emission characteristics. Evenwith resolution of these issues, all predictionsof future methane emissions are basedon the accurate simulation and prediction ofhigh-latitude climate. Improvements of manyaspects of modeling the high-latitude climatesystem are required, including improvementsto the treatment of snow, polar clouds, subsoilprocesses, subpolar oceans, and sea ice in globalclimate models.7. Final PerspectivesAlthough the prospect of a catastrophic releaseof methane to the atmosphere as a result ofanthropogenic climate change over the nextcentury appears very unlikely based on currentknowledge, many of the processes involvedare still poorly understood, and developing abetter predictive capability requires furtherwork. On a longer time scale, methane releasefrom hydrate reservoirs is likely to be a majorinfluence in global warming over the next 1,000to 100,000 years. Changes in climate, includingwarmer temperatures and more precipitation insome regions, will likely increase the chronicemissions of methane from both meltinghydrates and natural wetlands over the nextcentury. The magnitude of this effect cannot bepredicted with great accuracy yet, but is likelyto be equivalent to the current magnitude ofmany anthropogenic methane sources, whichhave already more than doubled the levels ofmethane in the atmosphere since the start ofthe Industrial Revolution.201