Article by Adrian Reid

1 November, 2019

Rising temperatures and a thaw in the world's vast reserves of methane, a potent greenhouse gas, delivered a series of lethal pulses in global temperatures 252 million years ago, in the final stages of the world's most deadly extinction, the Permian extinction. Scientists are drawing parallels with rising temperatures and methane levels today.

Article by Adrian Reid

1 November, 2019

A lesson for humanity

In a period of runaway climate change 252 million years ago, around 96% of sea life and 70% of life on land were wiped out. This period, the Permian extinction, experienced the largest loss of life in the Earth's history, and it was due to climate change. 

A study entitled "Methane hydrate: Killer cause of Earth's greatest mass extinction", conducted by Dr Uwe Brand, Brock University in Canada, and colleagues, says methane was the ultimate trigger for the mass extinction. The scientists say, this is "a lesson for humanity".

Wide-scale volcanic eruptions led to extremely high levels of carbon dioxide (CO2), followed later by dangerous amounts of methane gas. The result was an increase in global temperatures by about 10 degrees Celsius (18 °F), according to researchers.

With measurements of methane gas increasing dramatically and abruptly, particularly around the Arctic Ocean, it is a lesson we may not have much time to learn.

Methane gas

Although methane may get less attention than carbon dioxide (CO2), it is a greenhouse gas with much more power to heat the Earth. As a greenhouse gas, methane is 86 times stronger than CO2, over 20 years. Over 100 years, methane is 34 times stronger than CO2.

Methane is created from decaying organic matter such as dead plants or animals. Just like rotting food in a broken fridge, bacteria works to break down the material into CO2 or methane, depending on how much oxygen there is and how warm it is.

Over thousands of years, huge amounts of organic matter, such as leaves and trees, have become buried under permafrost in the Arctic region, across Siberia, Alaska, Northern Canada and parts of Scandinavia.

With global warming, this organic matter has now begun to thaw and decay, and break down into either CO2 or methane. Scientists are now detecting high levels of methane around the Arctic, in the air and bubbling up from lakes.

Methane under pressure

Methane also has a more ancient source. As ice ages came and went, some of the organic matter trapped in the permafrost thawed, converted into methane, and froze again. For millenia, the methane remained trapped deep in permafrost and under the Arctic Ocean. Under pressure, it formed an unusual, lattice-shaped molecule called methane hydrate, also known as "fire ice". 

Methane hydrate — methane trapped in an ice crystal

Methane hydrate is methane trapped within an ice crystal. It is a potentially explosive, flammable compound. Scientists estimate between 500-2000 gigatons of methane hydrate exist in the Arctic.

For millennia, permafrost has acted like a giant lid, a layer of frozen earth across the Arctic, that held methane hydrate securely underground. With increasing temperatures, that protection is quickly melting away.

Climate researchers predict that with global warming of 2  °C (3.6 °F), over 40% of the current permafrost area will disappear. If temperatures rise even further, to 5-6  °C (9.0-10.8 °F), they predict that the permafrost covered area could come close to disappearing.

The permafrost thaw has scientists worried. As glaciologist Dr Jason Box tweeted, there is so much methane trapped under the Arctic permafrost that if even a small fraction reaches the atmosphere, "we're f'd".

Rising methane levels

Measurements from all around the world show methane levels in the atmosphere are rising. But in some parts of the world, methane levels are rising in sudden, unpredictable ways.

In the South Pole, methane levels rise and fall regularly with the season.

South Pole methane measurements 2011-2019, plotted with the Interactive Atmospheric Data Visualization (IADV) Tool. USGS, NOAA, Public domain

In the Arctic, methane measurements show sudden, upward spikes in methane levels, and they are getting bigger each year.

Tiksi methane measurements 2011-2019, plotted with the Interactive Atmospheric Data Visualization (IADV) Tool. USGS, NOAA, Public domain

The methane must be coming from somewhere.

The Arctic environment

The large reserves of methane in the Arctic are due to its unique environment. Since the last Ice Age, the great Siberian and North American rivers have washed organic matter such as dead leaves or wood into the Arctic Ocean. Organic matter is then trapped under the icecap and frozen seafloor where it remains for thousands of years.

Microbes work even in this frozen environment to break down the organic matter, but without oxygen, they produce methane. Over time, microbes have produced enormous reserves of this gas.

The Arctic environment is now changing. In recent years the Arctic has been warming. The Arctic icecap has been shrinking, allowing more sunlight to warm the ocean and thaw the permafrost. Warmer currents from the Atlantic Ocean have made their way north, and the Arctic rivers have brought with them water warmed from the lower latitudes, melting the icecap and permafrost even more.

The Arctic Ocean is also the world's shallowest ocean. This is partly due to the Siberian Shelf, which is the world's largest continental shelf. Its average depth is 100 metres (110 yards) but it extends 1500 kilometres (932 miles) north of Russia. The ocean's shallowness also makes it both easier for the permafrost to thaw, and for the methane gas to escape from the sea floor into the atmosphere.

Major rivers carry organic matter like wood and leaves into the Arctic Sea. Over time this decomposes into methane. ©2004, ACIA/ Map ©Clifford Grabhorn, free for non-commercial use

Supersaturated seas

To hopefully dispel, or otherwise confirm fears about Arctic methane, research expeditions have made their way across the Arctic Ocean, measuring methane levels as they go.

Methane escaping into the atmosphere Tomsk Polytechnic University, Vitalii Sdelnikov, news@tpu.ru, sdelnikov@tpu.ru

In the deep Arctic Ocean north of Norway, between Svalbard and Greenland, scientists from the U.K.'s National Oceanography Centre found that the ocean is "supersaturated with methane".

Luckily little of the methane reached the atmosphere. In the deep water near Svalbard the methane could simply dissolve and float away. Or it could be eaten by methanotrophs — microbes which live off methane.

Russian scientists naturally focused on their backyard, the shallow East Siberian Arctic Shelf. There they found extreme supersaturation of methane in the ocean, up to 5000% more than in the atmosphere.

They also found that methane was reaching the atmosphere. About 70% of methane released from a depth of 6 metres (6.5 yards) reached the surface.

The Swedish research expedition, SWERUS, provided some confirmation for the Russians' results. The shallow waters of the East Siberian Arctic Shelf had higher levels of methane than anywhere else in the Arctic Ocean.

The high levels of methane in the East Siberian Arctic Shelf concerned the Russians and many others too, and provide support for to an alarming hypothesis.

The clathrate gun hypothesis

The clathrate gun hypothesis is the theory that methane can rapidly thaw and lead to sudden rises in global temperatures. It's a controversial topic among climate scientists. The concern is that it could be happening now.

Russian scientists, of which Dr Natalia Shakhova of the University of Alaska, Fairbanks is the most well-known, are more concerned about a clathrate gun.

They say "an abrupt release" of up to 50 gigatonnes of methane hydrate is "highly possible .. at any time", leading to "catastrophic greenhouse warming".

Their concern is that destabilisation of the permafrost in the shallow and seismically active East Siberian Shelf could occur unpredictably.

Reasons for this could be an earthquake, warmer temperatures, or even storm activity, any of which could result in the release of large amounts of methane.

Dr Carolyn Ruppel, leader of the USGS Gas Hydrates Project, believes there is no evidence of a clathrate gun. She says, there is "no conclusive proof that hydrate-derived methane is reaching the atmosphere".

In a related USGS blog, she states "most of the methane released by gas hydrates never reaches the atmosphere. Instead, the methane often remains in the undersea sediments, dissolves in the ocean, or is converted to carbon dioxide by microbes in the sediments or water column."

In an alternative literature review, U.K. Prof. Rachel James of the National Oceanography Centre and colleagues conclude that the methane does reach the atmosphere, as long as "the bubbles are large and water depth is shallow".

This conclusion seems to have been confirmed by the latest Russian expedition to the East Siberian sea. The team of 65 international scientists witnessed what they described as "megafountains" of methane at levels 9 times higher than normal.

Prof. Igor Semiletov, the head of the expedition says, "This result makes us radically revise a position that underwater permafrost is stable and will have melted only a few meters by the end of the 21st century."

Back to the Permian

The Permian extinction, like many other extinctions in the history of this planet, was due to climate change, and to carbon. The extinction began with wide-scale volcanic activity across Siberia, intense enough to cover the region in a kilometre-deep layer of lava. These eruptions also ignited huge amounts of coal buried underground, which over the next few thousand years released an estimated 3000 gigatonnes of carbon into the atmosphere.

With so much carbon in the atmosphere, there was runaway global warming. Earth scientist Uwe Brand found that "initial global warming of 8-11 degrees Celsius" during the Permian period was due to CO2 emissions, which then "triggered the release of .. methane from permafrost and .. methane hydrates", leading to the mass extinction of planetary life that followed. It took 20 million years for life to recover.

Are we on the same path again? Since the 1850s when the Industrial Revolution started, we have burned enough coal and oil to release about 600 gigatons of carbon. That is 20% of the 3000 gigatons released in the Permian extinction.

CO2 levels and temperature closely match. Philippe Rekacewicz, Emmanuelle Bournay, UNEP/GRID-Arenda, CC BY-NC-SA 2.0

As CO2 rises, temperatures follow. Ice samples show how temperature and CO2 levels have risen in the past. More than once, CO2 levels have come close to 300 parts per million (ppm), and each time, global temperatures have soared to 2-3 °C (3.6-5.4 °F) higher than normal. Now, CO2 levels are over 400 ppm, and are still climbing. Meteorologists describe this as "uncharted territory". In the history of the human race, we have never before been faced with a future such as this. 

During the Permian period, rising CO2 levels and temperatures were followed by a massive pulse of methane, which erased life in that era. At what temperature a methane 'burp' could take place again can only be estimated. Chances are, by that point, most of us will not be around to see it.