FROZEN HEAT | Volume 1

Estimates of the global methane content in gas hydrates fell as researchers began linking gas hydrate occurrence to the supply of organic material from which methane could be generated. Since the early 1980s, global estimates have varied widely (blue region in Fig. 1.6), reflecting continued uncertainties regarding the amount of methane delivered to, and subsequently stored in, the hydrate stability zone (Buf- fett and Archer 2004; Wood and Jung 2008). Significant reduction of the uncertainty associated with global estimates will require additional mapping and coring to define local and regional patterns of gas hydrate distribu- tion (Archer 2007) and to improve our basis for estimating porosity and gas hydrate saturation in unexplored regions. Such assessments are now underway, resulting in more rigorously constrained estimates for some of the world’s promising production regions (see Volume 2 Chapter 2), as well as for regions that are sensitive to climate change (see Volume 1 Chapter 3). As shown in Figure 1.7, even a median estimate of 5 000 Gt of methane carbon in methane hydrate represents a sig- nificant fraction of the world’s organic carbon, and is of similar magnitude to the combined estimates of carbon in traditional global fossil fuel resources, such as oil, coal, and natural gas. Not only is the gas hydrate estimate uncertain, however, but not all gas hydrates are equally accessible as an energy resource (see Volume 2 Chapter 2) (Boswell and Collett 2011). Nonetheless, with annual global consump- tion estimated at 1.8 Gt of methane carbon in 2011 and 2.15 Gt in 2020 (U.S. Energy Information Administration 2010), recovering even a small fraction of the methane in gas hydrates could significantly affect the global energy mix (see Volume 2).

Carbon mass in gas-hydrate-bound methane compared to other sources of organic carbon

0 1 000 2 000 3 000 4 000 5 000 6 000 10 000 Gigatonnes of Carbon

Gas hydrates Energy resources Other major pools

Natural gas Coal Oil

Peat Vegetation Detrital organic matter

Frozen soils Non-frozen soils Dissolved in water

Figure 1.7: Carbon mass in gas-hydrate-bound methane compared to other sources of organic carbon. A 2008 workshop estimated the global methane content in gas hydrates to range from 1 000 to 10 000 gigatonnes of carbon (GtC) (Krey et al. 2009). Taking a midrange value of 5 000 GtC as an example, gas hydrates would account for ~33 per cent of Earth’s organic carbon (excluding dispersed carbon such as bitumen and kerogen). Other major carbon pools and their mass estimates in GtC are presented here in top-to-bottom order as they are displayed in the figure. Values for vegetation and non-frozen soil are taken from Sabine et al. (2004), frozen soils from Tarnocai et al. (2009), peat from Limpens et al. (2008b, a), detrital matter from Matthews (1997), and atmospheric values from Blasing (2013). All other values are from Sundquist and Visser (2003).

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