These changes will have cascading effects on key regional bio-physical systems and cause global climatic feedbacks (very high confidence). (IPCC 2007, AR4 WG2 15) Methane Hydrate Instability / Permafrost Methane: Methane hydrates are stored on the seabed along continental margins where they are stabilised by high pressures and low temperatures, implying that ocean warming may cause hydrate instability and release of methane into the atmosphere. Methane is also stored in the soils in areas of permafrost and warming increases the likelihood of a positive feedback in the climate system via permafrost melting and the release of trapped methane into the atmosphere. Both forms of methane release represent a potential threshold in the climate system. As the climate warms, the likelihood of the system crossing a threshold for a sudden release increases. Since these changes produce changes in the radiative forcing through changes in the greenhouse gas concentrations, the climatic impacts of such a release are the same as an increase in the rate of change in the radiative forcing. (IPCC 2007, AR4 WG1 8.7.2.4) Global Climate Projections: [S]ome sources of future radiative forcing are yet to be accounted for in the ensemble projections, including those from land use change, variations in solar and volcanic activity […], and CH4 release from permafrost or ocean hydrates. (IPCC 2007, AR4 WG1 10.5.1) Assessing Key Vulnerabilities and the Risk from Climate Change: AR4 temperature range (1.1-6.4°C) accounts for this [climate-carbon cycle] feedback from all scenarios and models but additional CO2 and CH4 releases are possible from permafrost, peat lands, wetlands, and large stores of marine hydrates at high latitudes. (IPCC 2007, AR4 WG1 Table 19.1) Conclusion
These changes will have cascading effects on key regional bio-physical systems and cause global climatic feedbacks (very high confidence). (IPCC 2007, AR4 WG2 15) Methane Hydrate Instability / Permafrost Methane: Methane hydrates are stored on the seabed along continental margins where they are stabilised by high pressures and low temperatures, implying that ocean warming may cause hydrate instability and release of methane into the atmosphere. Methane is also stored in the soils in areas of permafrost and warming increases the likelihood of a positive feedback in the climate system via permafrost melting and the release of trapped methane into the atmosphere. Both forms of methane release represent a potential threshold in the climate system. As the climate warms, the likelihood of the system crossing a threshold for a sudden release increases. Since these changes produce changes in the radiative forcing through changes in the greenhouse gas concentrations, the climatic impacts of such a release are the same as an increase in the rate of change in the radiative forcing. (IPCC 2007, AR4 WG1 8.7.2.4) Global Climate Projections: [S]ome sources of future radiative forcing are yet to be accounted for in the ensemble projections, including those from land use change, variations in solar and volcanic activity […], and CH4 release from permafrost or ocean hydrates. (IPCC 2007, AR4 WG1 10.5.1) Assessing Key Vulnerabilities and the Risk from Climate Change: AR4 temperature range (1.1-6.4°C) accounts for this [climate-carbon cycle] feedback from all scenarios and models but additional CO2 and CH4 releases are possible from permafrost, peat lands, wetlands, and large stores of marine hydrates at high latitudes. (IPCC 2007, AR4 WG1 Table 19.1) Conclusion
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