Methane the greenhouse gas-Box 2

	Published by Australian Academy of Science
Excuse me! The problem with methane gas Box 2 \| The oceans’ massive methane reserves

While atmospheric methane levels are a concern, some researchers believe the real threat is methane trapped in our oceans.

As well as the methane that exists below permafrost on the land in polar regions, there are vast reserves stored in ocean floor sediments as methane hydrates. Here, methane molecules are each surrounded by a water crystal ‘cage’, so they are basically encased in ice. Although at the high pressures experienced in the deep ocean, these can exist at temperatures well above zero degrees Celsius. These hydrates, or clathrates, are the largest reserves of methane in the world, and by some estimates consist of more than half of all fossil fuels.

The vast stores of methane hydrates under the oceans are methane molecules trapped within water crystal ‘cages’.
(Image: USGS)

The concern is that rising sea temperatures will melt the hydrates, and lead to massive releases of methane. This could give way to a cycle in which the released gas results in more warming, causing more hydrates to melt, and the release of even more methane. This is what’s known as the ‘clathrate gun hypothesis’ which has been put forward to explain the mass extinction of marine and land-based life in the Permian era some 250 million years ago.

To some people, such a scenario is the stuff of science fiction, and the clathrate gun hypothesis has already featured in several novels.

But the clathrate gun might not go off – at least not just yet. Recent groundbreaking research involving Australian scientists has helped allay such concerns. The research involved scientists from CSIRO and Australian Nuclear Science and Technology Organisation (ANSTO), along with researchers from Denmark, New Zealand, and the United States. They used accelerator mass spectrometry and carbon dating to analyse the methane trapped in bubbles in ice cores from Greenland. The ice cores dated back to the end of the Younger Dryas period – known as the Big Freeze – about 12,000 years ago when there was a 50 per cent increase in global methane levels.

The good news is that the research found that the big increases in methane were produced from wetlands, and not hydrates under the ocean.

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