Fear of ancient methane ignores the greater climate crisis issue, scientists say

20 Feb 2020

Image: © Perytskyy/Stock.adobe.com

Researchers have looked at the potential damage caused by ancient methane reservoirs, and said that humans are still the greatest climate threat.

With the climate crisis showing no signs of abating, there are now fears that enormous quantities of potent greenhouse gases such as methane will emerge and rapidly speed up the destruction of Earth’s climate. These sources come from vast reservoirs of ancient carbon that emerge from permafrost in the soil and methane hydrates deep in the ocean.

However, researchers from the University of Rochester have analysed what potential impact the release of methane reservoirs would have on our planet, revealing that such fears of a surge in atmospheric methane are the least of our problems.

Their research, published to Science, found that even if methane is released from these large natural stores, very little actually reaches the atmosphere.

“One of our take-home points is that we need to be more concerned about the anthropogenic emissions – those originating from human activities – than the natural feedbacks,” said graduate student Michael Dyonisus.

What are methane hydrates?

Permafrost often contains organic carbon frozen for years at a time, originally sourced from dead plants. As temperatures rise and the ice melts, the underlying soil becomes waterlogged, creating the perfect environment for microbes to consume the carbon and create methane.

On the other hand, methane hydrates are mostly found in ocean sediments along the greatest depths of continental margins. In methane hydrates, cages of water molecules trap methane molecules inside. When ocean temperatures rise, so too will the temperature of the ocean sediments, causing the methane hydrates to destabilise and release the methane gas.

As part of this latest study, the researchers collected ice core samples from Antarctica – time capsules from Earth’s last deglaciation period between 8,000 and 15,000 years ago. Analysing the carbon-14 isotope of methane in the samples, the group found that methane emissions from the ancient carbon reservoirs were small.

“The likelihood of these old carbon reservoirs destabilising and creating a large positive warming feedback in the present day is also low,” Dyonisus said.

Benefit of ‘natural buffers’

In explaining why this is the case, the researchers said it is likely due to several “natural buffers”.

In the case of methane hydrates, if the methane is released in the deep ocean, most of it is dissolved and oxidised by ocean microbes before it ever reaches the atmosphere.

Meanwhile, if methane in permafrost is formed deep enough in the soil, it might be oxidised by bacteria that eat methane. Or the carbon in the permafrost may never become methane and, instead, be released as CO2.

Vasilii Petrenko said that human methane emissions are currently larger than wetland emissions “by a factor of about two”.

“Our data shows we don’t need to be as concerned about large methane releases from large carbon reservoirs in response to future warming; we should be more concerned about methane released from human activities,” he said.

Colm Gorey was a senior journalist with Silicon Republic