Thawing of Methane Hydrates

Introduction

(click image to enlarge)
Methane Escaping from the East Siberian Arctic Shelf
Image Courtesy of the National Science Foundation

One potentially important environmental issue in the case of natural gas does not bear on the use of natural gas as a fuel, but arises from the fact that methane has extensive presence in the soil and waters of frozen regions in and surrounding the Arctic Ocean. Those regions have recently been warming as a result of increasing global temperatures, and methane is being released.


Methane is a greenhouse gas, about 20 times as powerful as carbon dioxide. It is present in large quantities in:

  • the Arctic in natural gas deposits,
  • in the permafrost layer on both exposed land and the submerged floor of the East Siberian Arctic Shelf,
  • and as submarine methane hydrates.
As these areas warm, they release frozen methane into the atmosphere at increasing rates.


The effects of Arctic warming on the global climate are as yet uncertain, but the potential for abrupt climate change due to this phenomenon has become a major concern for scientists worldwide. Some scientists have proposed that this could become the "tipping point" that sends climate change on the earth into an irreversible, positive feedback loop of increasing global warming.

Methane Hydrate Characteristics

Methane Hydrate
(water: red and white; methane: silver and green)
source: USGS

A methane hydrate is a type of clathrate, which is a molecular lattice containing an entrapped compound. In the case of a methane hydrate, the clathrate is a lattice "cage" formed of water molecules (H2O), within which is trapped one or more methane (CH4) molecules.


In order to preserve the hydrate structural stability, the temperature and pressure must be at levels that maintain the system in an ice form. Methane hydrates have been found in the permafrost of such land areas as Siberia and Alaska, where the year-round temperature does not rise above 0° Celsius. In ocean environments methane hydrates are extensive in sediments at shallow depths, not exceeding 2000 meters below the surface. In all cases the temperature is sufficiently low to maintain the ice structure year round. Methane hydrates have also been found in fresh water lakes in polar regions of Siberia.


Environment

The environmental dangers associated with methane hydrates center around:

  • the extensive amount of methane hydrates present in both oceanic and land-based, permafrost environments,
  • the vulnerability of frozen hydrates to increases in temperature, and
  • the powerful greenhouse gas properties of methane, when compared to carbon dioxide.


In the case of permafrost, the potential for release of methane due to global warming is considerable and could lead to a "snowball" effect. If global warming produced an extensive thawing of permafrost, resulting in a release of copious amounts of methane into the atmosphere, this release would result in a positive feedback loop, with further warming of the environment, causing more thawing of permafrost, with the subsequent release of even more methane and more heating of the environment.