Methane actively dissociating from a hydrate mound

It is known that gas hydrates in natural environments are highly unstable. Although human activity in deep water has the potential to initiate small-scale and local hydrate dissociation, these impacts are likely to be negligible in a global climate context. However, there are many ongoing natural phenomena, including sediment deposition and erosion (including occasionally catastrophic failure of continental slope), subsidence and uplift of the sea floor, global climatic cycles, changes in ocean circulation patterns, and changes in global sea level, that continually alter the temperature and pressure profiles in the shallow sea-bottom sediments. These processes, which operate at continental to global scales, continually impact the stability of natural methane hydrate, resulting in occasional, and potentially massive, destabilization of natural gas hydrates. If this methane somehow enters the atmosphere, it will reside there for roughly 10-20 years, during which time it will act as a very efficient greenhouse gas (gases that trap solar radiation and therefore, in sufficient quantities, have the potential to contribute to global climate change). In fact, methane gas has roughly 10 times more heat-trapping capacity than carbon dioxide (CO2), the most notorious greenhouse gas. Over the longer term, the atmospheric impact of methane will continue at lesser levels as the methane slowly dissipates through oxidation into water and CO2.

Current research is focused on determining the scale and nature of gas hydrate occurrence (how much is there, where is it, what lithology is it encased in, etc.) and whether the methane in hydrates is securely sequestered, or if it can, either slowly and methodology, or through rare catastrophic events, find its way to the atmosphere. Arctic gas hydrates may be the most likely to reach the atmosphere if destabilized, however, the volume of hydrate in the arctic is relatively small when compared to marine sources. Most of the methane introduced into the sea from marine gas hydrates will likely not reach the atmosphere, due to mixing and intense biological oxidation in the water column. However, it has been suggested that rare events in Earth history, such as the Paleocene-Eocene Thermal Maxima (55 million years ago) may be related to massive releases of methane from hydrates from multiple locations over geologically-short time scales triggered by changes in sea-water circulation patterns and sea-bottom temperature, or to reductions in sea-floor pressures due to dramatic lowering in global sea-level. Such large-scale releases may overwhelm the capability for the ocean to sequester the methane, resulting in vast amounts of methane introduction to the atmosphere that lead to changes in global climate. Much more needs to be known, including the routine flux and fates of methane emissions from the seafloor, as well as the potential for large-scale destabilization of gas hydrates, the ability of dissociated methane to reach the sea-floor surface (and related issues of sea-floor stability and large-scale failure of the continental slope), the potential for such releases to reach the atmosphere, and the attendant impact the global oceanic carbon cycle, and global climate. Critical to this effort will be studies of both current processes through deep sea observation and numerical modeling, as well as study of the geologic record of past abrupt climate change and the potential role that methane from gas hydrates may have played

Geological evidence, including remnants of past ice-ages and chemical analyses of ancient air trapped in the thick ice sheets of Greenland and Antarctica, confirms that the Earth’s global climate has changed significantly and continually through time. In the geologically recent past, these changes have been marked by periodic ice ages. Most scientists explain these changes as results of regular perturbations in both the Earth’s orbit and the inclination of the Earth’s axis relative to the sun. However, one item was difficult to explain - although ice ages appeared gradually, they seemed to end abruptly. Analyses of ice cores indicates that atmospheric contents of CO2 and methane show the same pattern; slow reduction at the onset of the ice ages and rapid increase roughly coincident with the end of the ice age. Presently, there is no consensus on what natural processes best explain rapid methane build-up in the atmosphere. One intriguing possibility is the large-scale dissociation and release of methane from natural gas hydrate deposits.

Alternative Estimate of the Distribution of Organic Carbon Within the Earth