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sediment and may cause submarine landslides and simultaneously release methane
into the atmosphere. The methane released from the reservoir to the atmosphere can
contribute to the climate change. Submarine landslides can cause tsunamis and catastrophic coastal flooding. The thickness of the gas hydrate stability zone (GHSZ) in
continental margins depends on water depth (hydrostatic pressure), water temperature,
geothermal gradient, and gas composition [1,60] (Tohidi, 2013, pers. comm.).
Methane is a powerful greenhouse gas. Despite its short atmospheric half-life of
seven years, methane has a significant global warming potential [1–15] (Harrison,
2010, pers. comm.). Recent research carried out in 2008 in the Siberian Arctic has
shown millions of tons of methane being released [153,162,166,168,169,176] (Kennett,
2012, pers. comm.), with concentrations in some regions reaching up to 100 times
above normal [1–16] (Harrison, 2010, pers. comm.). Past and future climate changes
can be linked to methane released from gas hydrates.
Currently, the link between stability of gas hydrates and global warming is being
examined. Since methane warms the environment 15–20 times more than carbon
dioxide, the release of methane can create a chain reaction for global warming, leading to more hydrate instability with additional release of methane. Methane release
in air eventually (within 10 years) is converted to carbon dioxide, another greenhouse gas [117–180] (Kennett, 2012, pers. comm.).
The analysis of the link between gas hydrate and climate warming can be divided
into five parts [117–180] (Kennett, 2012, pers. comm.):
Region 1: Thick (≥300 m) onshore permafrost. Gas hydrates that occur within
or beneath thick terrestrial permafrost will remain largely stable even if climate warming lasts hundreds of years. The warming could, however, cause
hydrates at the top of the stability zone, about 625 ft below the earth’s surface to dissociate over thousands of years [117–180] (Kennett, 2012, pers.
comm.). It contributes <1% of the total hydrates, and its effect on climate
change will be minimal.
Region 2: Subsea permafrost on the circum-Arctic shelves. The shallow water
continental shelves that circle the parts of the Arctic Ocean were formed
when sea-level rise during the past 10,000 years inundated permafrost that
was at the coastline. The methane hydrates in subsea permafrost that is
thawing beneath these continental shelves is being released now. While this
methane can rise to ocean surface and then to atmosphere, the amount is
only considerably less than about 1% of the world gas hydrates [117–180]
(Kennett, 2012, pers. comm.).
Region 3: Upper edge of stability (or deep-water marine hydrates at the
feather edge of GHSZ). Gas hydrates on upper continental slopes beneath
1000–1600 ft of water lie at the shallowest water depth for which methane
hydrates are stable. The upper continental slopes that ring all the continents
could host gas hydrates in zones that are roughly 30 ft thick. Within the next
100 years, warm water can completely dissociate these hydrates, but they
are more likely to be oxidized in water than released in the atmosphere.
These hydrates contribute about 3.5% of the earth’s total hydrates [117–180]
(Kennett, 2012, pers. comm.).