Catastrophic Methane Hydrate Release Mitigation

This topic falls under the category of abrupt climate change as will be clear shortly. Methane hydrates or clathrates are combinations of water and methane in the form of an ice-like matrix. The methane is the result of the action of methanogenic bacteria on sediment over thousands of years. The methane is kept in an ice form where appropriate combinations of temperature and pressure exist.

Methane hydrates are widespread in sea sediments hundreds of meters below the sea floor along the outer continental margins and are also found in Arctic permafrost. Some deposits are close to the ocean floor and at water depths as shallow as 150 m, although at low latitudes they are generally only found below 500 m. The deposits can be 300-600 m thick and cover large horizontal areas. A nearby deposit nearly 500 km in length is found along the Blake Ridge off the coast of N.C. at depths of 2000-4000 m.

The total quantity of methane hydrates in the ocean sediment is estimated to be around 10,000 GtC. The methane hydrates in sediment considered part of U.S. territory alone could supply U.S. natural gas needs for 1000 years. Because of this enormous quantity, methane hydrates are being investigated as an energy source to replace petroleum and conventional sources of natural gas, although an extraction technology for ocean sediments does not presently exist.

There is some evidence that massive releases of methane from ocean sediment hydrate deposits may have been indirectly responsible for ending some of the ice ages. Were such releases to occur today because of warming of the oceans or as a result of seismic events, the result could be a sudden rise in atmospheric temperature, triggering feedback mechanisms that might lead to rapid melting of polar ice.

In the slides, the example of a 1 GtC release was used. That represents 0.01% of the total methane hydrates in the ocean. The quantity degassed to the atmosphere 15,000 years ago, at the end of the last ice age is now believed to be around 4 GtC as methane or 0.04%. The average temperature of the Earth increased from 30°F to 60°F within a few decades. The radiative forcing from the methane alone would have been insufficient to cause more than a 3°F increase. It is thought that feedback effects from additional methane released from melting permafrost, carbon dioxide and water vapor contributed to the rest of the warming. But the initial methane hydrate release from the ocean may have been the catalyst.