FROZEN HEAT | Volume 1

3.1 INTRODUCTION

As discussed earlier in this report, methane in the atmos- phere is a potent greenhouse gas. Methane’s radiative forcing value, a measure of how it changes Earth’s balance between incoming and lost solar energy, is about 0.5 watts per square metre, second only to the 1.66 watts per square metre of car- bon dioxide (IPCC 2007). The atmosphere contains about 3.7 Gt of methane carbon (IPCC 2007). This value is reasonably constant because of a delicate balance between atmospheric methane input and removal rates, both in the range of 0.45 Gt of methane car- bon per year (IPCC 2007). Taking the midrange estimate of 5 000 Gt of carbon held as methane sequestered in gas hydrates (see Volume 1 Chapter 1), an instantaneous release of just a tenth of a per cent of Earth’s gas hydrates to the

atmosphere would more than double the IPCC’s estimated atmospheric methane concentration.

Methane’s greenhouse potency, combined with the amount of methane stored in gas hydrates, has led researchers to sug- gest methane released from dissociating gas hydrates played a significant role in past climate changes, and could be an important factor in future climate change. This chapter pre- sents an example of how gas hydrates have been connected to past climate change and discusses key factors in establishing the role of gas hydrates in future climate change. Future cli- mate change scenarios and the possible response of marine and permafrost gas hydrate deposits are then considered. The chapter concludes with a summarized assessment of the deposits that are most susceptible to change.

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