Wobbly planet triggered massive methane burps

Three huge eruptions of methane 180 million years ago triggered a catastrophic increase in global temperatures, according to research funded by the Natural Environment Research Council (NERC). The results, which are published in the current issue of Nature, could provide clues about the global warming process most scientists agree we are experiencing today.

Geochemical analysis of mudrocks along the Yorkshire coast suggest that the methane was released when gas hydrate, a frozen mixture of water and methane, escaped from the seabed in huge quantities. The hydrate would have melted during one of the slight wobbles in the Earth’s orbit that bring our planet closer to the Sun. This can warm the oceans, enough to melt the reserves of hydrate.

PhD student Dave Kemp explains that once the methane was released into the atmosphere, it would have reacted with oxygen to form carbon dioxide, a much longer-lived greenhouse gas. The CO₂ would then have been responsible for the prolonged period of warming.

The Open University's Dr. Angela Coe and Dr. Anthony Cohen, explain that the methane burps triggered an increase of around 10°C in average global temperatures, which in turn caused the extinction of a large number of species.

Dr. Coe goes on: "We've known about this event for a few years through earlier work by our team and others, but there’s been a great deal of uncertainty about its precise size, duration, and underlying cause. What our present study shows is that this methane release was not just one event, but 3 consecutive pulses that occurred within a 60,000 year interval."

Each individual pulse was very rapid, she continues, and although the release was very quick, global recovery took much longer, occurring over a few hundred thousand years.

The researchers say that the work provides an accurate picture of how the planet reacts to a sudden increase of atmospheric CO₂.

"Today we are releasing large amounts of carbon dioxide to the atmosphere, primarily through the burning of fossil fuels. It is possible that the rate at which carbon dioxide is being added to the atmosphere now actually outstrips the rate at which it was added 180 million years ago," says Dr. Cohen. "Given that the effects were so devastating then, it is extremely important to understand the details of past events in order to better comprehend present-day climate change."

Dr. Lorenz Schwark of the University of Cologne also contributed to the research. ®