Major hydrate GHG release unlikely

A comprehensive review of research publications indicates an absence of evidence for significant methane release into atmosphere

ALAN BAILEY

Petroleum News

People have speculated that the massive release of methane from methane hydrate deposits under the seafloor, as the Earth’s climate warms, could accelerate the warming process. Methane is a greenhouse gas that is much more potent than carbon dioxide, the bête noire of the global warming debate. The release of methane from warming hydrates could trigger what is referred to as a positive feedback, in which the methane accelerates the warming trend, thus causing increasing quantities of hydrate to break down.

But a recently completed interpretive review by the U.S. Geological Survey and the University of Rochester of research publications has indicated that a massive release of methane from hydrates is unlikely to happen, the USGS has announced.

Methane hydrate is an ice-like solid with methane trapped in a lattice of water molecules. The material, which can hold high concentrations of methane, is stable within a certain range of relatively high pressures and low temperatures. The hydrates occur naturally in various parts of the world, in situations where pressure and temperature conditions are appropriate to the material’s stability. Elevate the temperature above the hydrate stability zone, and the material will break down, releasing the methane.

The new review says that hydrates probably are currently breaking down at some locations because of the warming of ocean waters. But the methane emissions from this phenomenon are much less than the emission of greenhouse gases from human activities. And most of the methane released from hydrates never reaches the atmosphere. Instead, the methane often remains trapped in subsea sediments, becomes dissolved in the seawater or is converted to carbon dioxide by microbes.

Although some studies have noted elevated rates of methane moving from the ocean to the atmosphere in the Arctic, none of this methane has been traced to the breakdown of hydrates as a consequence of climate change. Nor is there any evidence that the methane emissions relate to longer term warming of the Earth since the last ice age, the USGS says.

“Our review is the culmination of nearly a decade of original research by the USGS, my co-author Professor John Kessler at the University of Rochester, and many other groups in the community,” said USGS geophysicist Carolyn Ruppel, the scientist who oversees the USGS Gas Hydrates Project. “After so many years spent determining where gas hydrates are breaking down and measuring methane flux at the sea-air interface, we suggest that conclusive evidence for release of hydrate-related methane to the atmosphere is lacking.”