Dear Readers, I would like to take you on a short emotional journey. I was browsing science headlines, and I came across one that had me worried for a good minute. Past climate warming driven by hydrothermal vents, with a sub-header specifying methane release from these vents as the driver of a warming event 55 million years ago. I imagine many of you already know why this caught my attention. Methane is well-known as a potent greenhouse gas, emitted by both fossil fuel extraction, and animal agriculture. It also exists in massive sea-floor deposits called “clathrates” or “hydrates”, in which a combination of low temperatures and high pressure create stable ice formations. The clathrate gun hypothesis is a proposal to explain warming during the Quaternary period, and it basically suggests that these deposits can destabilize, release all their methane, which would bubble up through the water into the atmosphere, driving an increase in global temperature.

The fear for us has been that this could be triggered by the warming of the oceans, adding fuel to the fire that is global warming. Last October, I posted about new research indicating that this was not actually likely to be a serious problem. See, getting the right combination of temperature and pressure for clathrates to form requires them to be deep enough under water, that the gas released by them is pretty much entirely absorbed:

New research from scientists at the University of Rochester, the US Geological Survey, and the University of California Irvine is the first to directly show that methane released from decomposing hydrates is not reaching the atmosphere.

The researchers, including John Kessler, a professor in the Department of Earth and Environmental Sciences, and DongJoo Joung, a former research scientist in Kessler’s lab and now an assistant professor in the Department of Oceanography at Pusan National University in Korea, carried out the study in mid-latitude regions—Earth’s subtropical and temperate zones.

While the stability of the methane hydrate reservoir is sensitive to changes in temperature, “in the mid-latitude regions where this study was conducted, we see no signatures of hydrate methane being emitted to the atmosphere,” says Joung, the first author of the study, published in Nature Geoscience.

Reading about this research was a load off my mind. There are a number of ways in which global warming could make things go sideways really fast. The jaw-dropping spike in ocean temperatures that we’ve been seeing this year have, I think, alerted more people to that possibility, but for a while, the clathrate gun was the thing that worried me the most. A big part of the problem with global warming is the speed at which it’s happening. If it had taken us ten thousand years to warm the earth this much, ecosystems might have been able to adapt better, and we would have had a much easier time ending fossil fuel use. Unfortunately, it’s taken us something more like 150 years, and that’s already more than we can handle, based on how things are going. A sudden, massive release of methane into the atmosphere could speed that up even more, and that would try even my ability to be optimistic.

So, I see this new headline, about methane emissions from hydrothermal vents, and I immediately think of the hydrothermal vents with which I’m most familiar – the ones that exist deep in the ocean, surrounded by tube worms and furry crabs. The last month has been pretty stressful for me, and I was not looking forward to hearing confirmation that deep-sea methane could, in fact, reach the surface.

Fortunately, that is not what I read.

About 55 million years ago, the Atlantic Ocean was born. Until then, Europe and America were connected. As the continents began to move apart, the Earth’s crust between them ruptured, releasing large volumes of magma. This rift volcanism has led to the formation of large igneous provinces (LIPs) in several places around the world. One such LIP was formed between Greenland and Europe and now lies several kilometres below the ocean surface. An international drilling campaign led by Christian Berndt, Professor of Marine Geophysics at GEOMAR Helmholtz Centre for Ocean Research in Kiel, Germany, and Sverre Planke, Professor of Marine Geophysics at the University of Oslo, Norway, has collected extensive sample material from the LIP, which has now been evaluated.

In their study, published today in the journal Nature Geoscience, the researchers can show that hydrothermal vents were active at very shallow depths or even above sea level, which would have allowed much larger quantities of greenhouse gases to enter the atmosphere than previously thought [emphasis mine].

Phew! Looks like we’re still in the clear.

With that anxiety now quelled, let’s take a look at how the researchers came to this conclusion, because it was quite the endeavor:

“At the Paleocene-Eocene boundary, some of the most powerful volcanic eruptions in Earth’s history took place over a period of more than a million years,” says Christian Berndt. According to current knowledge, this volcanism warmed the world’s climate by at least five degrees Celsius and caused a mass extinction – the last dramatic global warming before our time, known as the Paleocene-Eocene Thermal Maximum (PETM). Geologists have not yet been able to explain why, as most modern volcanic eruptions cause cooling by releasing aerosols into the stratosphere.

Further studies of the Karoo large igneous province in South Africa revealed an abundance of hydrothermal vents associated with magmatic intrusions into the sedimentary basin. This observation among others led to the hypothesis that large amounts of the greenhouse gases carbon dioxide and methane could have entered the atmosphere through hydrothermal venting. “When our Norwegian colleagues Henrik Svensen and Sverre Planke published their results in 2004, we would have loved to set off immediately to test the hypothesis by drilling the ancient vent systems around the North Atlantic,” says Christian Berndt. But it wasn’t that easy: “Our proposal was well received by the Integrated Ocean Drilling Program (IODP), but it was never scheduled because it required riser drilling, a technology that was not available to us at the time.”

As the research progressed hydrothermal vent systems were discovered that were within reach of riserless drilling. Thus, the drilling proposal was resubmitted, and the expedition could finally begin in autumn 2021 – 17 years after the first proposal was submitted.

Around 30 scientists from 12 nations took part in the IODP (now the International Ocean Discovery Program) research cruise to the Vøring Plateau off the Norwegian coast on board the scientific drilling ship “JOIDES Resolution”. Five of the 20 boreholes were drilled directly into one of the thousands of hydrothermal vents. The cores obtained can be read by scientists like a diary of the Earth’s history. The results were compelling.

The authors show that the vent was active just before the Paleocene Eocene Thermal Maximum and that the resulting crater was filled in a very short time, just as the global warming began. Quite unexpectedly, their data also show that the vent was active in a very shallow water depth of probably less than 100 metres. This has far-reaching consequences for the potential impact on the climate. Christian Berndt: “Most of the methane that enters the water column from active deep-sea hydrothermal vents today is quickly converted into carbon dioxide, a much less potent greenhouse gas. Since the vent we studied is located in the middle of the rift valley, where the water depth should be greatest, we assume that other vents were also in shallow water or even above sea level, which would have allowed much larger amounts of greenhouse gases to enter the atmosphere”.

As far as today’s climate warming is concerned, there are some interesting conclusions to be drawn from the cores. On the one hand, they do not confirm that the global warming at that time was caused by the dissolution og gas hyrates [sic] – a danger that has been much discussed in recent years. On the other hand, they show that it took many millennia for the climate to cool down again. So the Earth system was thus able to regulate itself, but not on time scales relevant to today’s climate crisis.

Reading that feels a bit like reading about a city built on top of another city, with the ancient ruins still down there to be explored. I get that in principle, this isn’t much different from taking any other geological core samples, but it feels different to me for some reason.

Regardless, while the researchers did not make this connection in these materials, I think that for our purposes, we can take some comfort from the shallowness of these ancient vents. Obviously, global warming is a crisis that demands great urgency, and this changes that not one bit. Clathrate gun or no, we are running out of time. The reason I wanted to share this (aside from it just being interesting research), is that I think it’s genuinely helpful to know at least one of the ways in which everything could get suddenly worse, isn’t something we need to worry about.

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