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A GLOBAL OUTLOOK ON METHANE GAS HYDRATES
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Gas
hydrates
Oceans
Wetlands
Primary sources of methane release
0
10
20
30
40
50
60
70
80
90
100
Wild
animal
emissions
Wildfires
Termite
emissions
Geological
sources
Coal
(Burned as fuel)
Oil andGas
(Burned as fuel)
Landfills
Biomass
burning
Ruminant
emissions
Rice
Paddies
Teragrammes
Methane mass released per year
Minimum
Maximum
231
Source: IPCC (2007)
Figure 2.2:
Primary methane emissions to the atmosphere per year. Methane emissions due to human-related activities, shown to the right
of the volcano, account for approximately 70 per cent of the total emissions (Reeburgh 2007; Colwell and Ussler III 2010). Gas Hydrates
are currently estimated to contribute about 5 Tg (Tg = 10
12
grammes) of methane (3.5 Tg carbon) per year to the atmosphere (IPCC, 2007).
Emission rates for gas hydrates are highly speculative, however, and may overestimate the atmospheric methane contribution by not
fully accounting for methane consumed by microbes in the sediment and water column (Fig. 2.3). Additional research will be required to
constrain the methane flux from gas hydrates that reaches the atmosphere.