There are parallels between today’s and past greenhouse gas-driven climate changes
August 1, 2017 — Coincidence doesn’t prove causality, as they say, but when the same two things happen together over and over again through the vast span of geological time, there must be a causal link. Of some 18 major and minor mass extinctions since the dawn of complex life, most happened at the same time as a rare, epic volcanic phenomenon called a Large Igneous Province (LIP). Many of those extinctions were also accompanied by abrupt climate warming, expansion of ocean dead zones and acidification, like today.
Earth’s most severe mass extinction, the “Great Dying,” began 251.94 million years ago at the end of the Permian period, with the loss of more than 90% of marine species. Precise rock dates published in 2014 and 2015 proved that the extinction coincided with the Siberian Traps LIP, an epic outpouring of lava and intrusions of underground magma covering an area of northern Asia the size of Europe.
But those rock dates presented science with a new puzzle: why was the mass extinction event much shorter than the eruptions? And why did the extinction happen some 300,000 years after the lava began to flow?
Now in a new study published in Nature Communications, Seth Burgess of the US Geological Survey, along with James Muirhead of Syracuse University and Samuel Bowring of MIT, think they have the answer. As Burgess told me:
Burgess noticed that the beginning of the mass extinction, as well as a jolt to the carbon cycle and abrupt climate warming, coincided exactly with a switch in the style of volcanic activity in the Siberian Traps. During the initial 300,000 years of the eruptions, basalt lava poured over a vast area of Siberia building to several kilometers thick. In this time there was some stress to life in the Northern Hemisphere, but no mass extinction. Life only began to disappear across the globe at exactly the same time that lava stopped erupting above ground, and instead began to inject as sheets of magma underground.
In other words, it wasn’t the lava, it was the underground magma that started the killing, by releasing greenhouse gases.
Norwegian scientist Henrik Svensen had earlier identified hundreds of unusual volcanic vents called “diatreme pipes” all over Siberia that connected underground intrusions of magma (“sills”) to the atmosphere, showing signs of violent gas explosions. This new work emphasizes the importance of Svensen’s 2009 conclusions:
Svensen, who was not involved in Burgess’ study, commented:
Greenhouse gas as a killer
While other scientists have proposed that an array of killers may have been involved in the end-Permian mass extinction, from mercury poisoning to ultraviolet rays and ozone collapse to acid rain, Burgess argues that it was principally greenhouse gas emissions triggered by magma intrusions that caused the extinction through abrupt global warming and ocean acidification. I asked him to outline the evidence for that.
He went on to explain various lines of evidence that point to the source of that carbon being methane and carbon dioxide resulting from magma intruding and cooking organic-rich sediments. He continued:
And then the third line of evidence is a physiologic selectivity to the marine mass extinction. Organisms that make their shells out of calcium carbonate suffer much higher mortality than organisms that make their shells out of silica, for example, which suggests that the ocean was acidified, and you get that by pumping gases like CO2 into the atmosphere.
That’s not to say that other factors had no role in ruining the environment:
A series of associated events
Coincidentally, Joshua Davies of the University of Geneva and colleagues have just narrowed down the trigger for the end-Triassic mass extinction, another of Earth’s biggest mass extinctions, to the underground phase of its associated Large Igneous Province. The Central Atlantic Magmatic Province (CAMP) is another enormous igneous province which stretches from Maine to South America, and includes the Palisade Sill visible from Manhattan.
They too used high precision rock dates on a vast sill that intruded organic rich sediments in the Amazon Basin, and found that this underground magma intrusion also coincided with the extinction. Like Burgess, Davies also argues that greenhouse gas baked from sediments drove climate change, which drove the mass extinction in a smaller repeat of the end-Permian events, this time 201.5 million years ago.
“I think CAMP is very similar to the Siberian Traps and that’s the reason why there’s an extinction at that time. I’m not surprised that they got similar results,” said Burgess.
Diatreme pipes from magma intrusions have also been identified as a likely cause for a more recent global warming and very minor extinction event – the Paleocene–Eocene Thermal Maximum (PETM) 56 million years ago. Again, prodigious quantities of greenhouse gases erupted from oil-rich deposits, although in that case it’s been hard to locate and date the “smoking gun” intrusions due to the fact that they are under the Atlantic Ocean.
A predictive model
Burgess’ insight makes a testable prediction:
This may explain why some Large Igneous Provinces are tied to mass extinctions, and some are not. Burgess thinks that the Deccan LIP, which happened at the time when the dinosaurs disappeared at the end of the Cretaceous, would not have triggered a major mass extinction on its own:
The more science learns of these past greenhouse gas-driven events, the more uncomfortable the parallels to today become. I asked Burgess if it was ridiculous to make the comparison.
Geologically fast buildup of greenhouse gas linked to warming, rising sea-levels, widespread oxygen-starved ocean dead zones and ocean acidification are fairly consistent across the mass extinction events, and those same symptoms are happening today as a result of human-driven climate change. Even though the duration of those past events was longer, and the volume of emissions was larger than we will produce, we are emitting greenhouse gases around 10 times faster than the most recent, mildest example – the PETM. The rapidity of today’s emissions prompted scientists Richard Zeebe and James Zachos to observe in a 2013 paper:
When the promises made for the 2016 Paris Agreement on climate change are added up, they aim to limit peak warming this century to about 3.3ºC compared to about 4.2ºC for the business-as-usual scenario, and the 2ºC limit the world is aiming to stay under. It’s sobering to compare those numbers to the majority of mass extinctions in the geological record which were characterized by abrupt warmings typically around 6-7ºC.