Methane Emissions & Global Warming

Natural Seeps Produce Methane

As seep bubbles rise to the ocean surface, substantial amounts of hydrocarbons dissolve in the water column, forming a subsurface gradient of dissolved hydrocarbons, principally methane. The remaining seep bubbles that do not dissolve continue to the surface and burst, releasing the gaseous components to the atmosphere.

http://www.sbcountyplanning.org/energy/information/seepspaper.asp#naturalSeeps

Methane is a Greenhouse Gas

The addition of methane to the atmosphere can have the following negative impacts (Wikipedia.org/Methane):

  • Methane is a relatively potent greenhouse gas with a high global warming potential (i.e., warming effect compared to carbon dioxide)
  • The major source of methane is extraction from geological deposits known as natural gas fields, which includes [offshore] natural gas seeps

Greenhouse Gases Contribute to Global Warming

  • Methane in the earth’s atmosphere is an important greenhouse gas with a huge global warming potential.  During the next 100 years, 1 ton of methane emission will have 25 times the impact on  the earth’s temperature as 1 ton carbon dioxide emission
  • Methane has a large effect for a brief period (about 10 years), whereas carbon dioxide has a small effect for a long period (over 100 years). Because of this difference in effect and time period, the global warming potential of methane over a 20-year time period is far greater (25 times more) than that of carbon dioxide.
  • Since 1750, the methane concentration has increased by about 150% and it accounts for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases.
  • At high pressures, such as are found on the bottom of the ocean, methane forms a solid clathrate with water, known as methane hydrate. An unknown, but possibly very large quantity, of methane is trapped in this form in ocean sediments. One source estimates the size of the methane hydrate deposits of the oceans at 10 trillion tons (10 exagrams). Theories suggest that this methane could again be suddenly released into the atmosphere  should global warming cause the oceans to heat up sufficiently.
  • The sudden release of large volumes of methane from such sediments into the atmosphere has been suggested as a possible cause for rapid global warming events in the earth’s distant past, such as the Paleocene-Eocene thermal maximum of 55 million years ago.