FROZEN HEAT | Volume 1

Teragrammes Methane mass released per year

Primary sources of methane release

231

100

Minimum Maximum

Ruminant emissions

Biomass burning

Wetlands

90

80

Landfills

70

Oil andGas (Burned as fuel)

Rice Paddies

60

Coal (Burned as fuel)

50

40

Termite emissions

30

Geological sources

Wild animal emissions

20

Wildfires

Oceans

Gas hydrates

10

0

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.

A GLOBAL OUTLOOK ON METHANE GAS HYDRATES 35

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