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Posted: Mar 23 2005, 07:57 PM
Joined: 12-February 05
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Catastrophic releases of methane gas from hydrates (clathrates) have the potential to cause rapid climate changes. Today, methane hydrates are stored along continental margins (i.e. at intermediate water depths, from 250 m to several thousand meters water depth), where they are stabilized by water pressure and temperature. Methane hydrates may become unstable under influence of ocean warming or slope instability1-2. The estimated present-day reservoir of carbon stored in methane hydrates1,3 is about 10,000 Gt (giga ton), which is a substantial amount compared to 38,000 Gt carbon stored in the oceans, 2000 Gt in soils and plants, and 730 Gt in the atmosphere4 . This implies that instability of these hydrates and the subsequent release of methane gas into the atmosphere could potentially cause strong climatic warming through an enhancement of the greenhouse effect.
The Paleocene/Eocene thermal maximum (PETM, ~55.5 Million years ago) is a well-known example from the past of a period with drastic climate change due to massive releases of methane from hydrates5-6. Carbon isotope measurements in ocean cores with sediments from the PETM suggest that 1500-2000 Gt of methane carbon was released within a few thousand years5,7-9. This massive methane release had a profound effect on climate. Paleoceanographical evidence from ocean cores indicates that ocean temperatures increased abruptly by 1°C to up to 8°C, depending on the location10-11. It has also been suggested that large temperature swings during the last glacial have been caused by abrupt releases of methane hydrates12-13. In addition, there is growing concern that the expected future global warming may lead to hydrate instability and thus to an enhanced emission of methane, imposing a strong positive feedback that amplifies anthropogenic warming. It is thus very important to quantify the impact of such a methane hydrate scenario on the climate system.
To study the climatic response to a massive methane release from gas hydrates, we have carried out two 2500-year long numerical experiments performed with a coupled atmosphere-sea ice-ocean model.