---

Here’s a pop quiz to help us through the midwinter blahs, followed by a two-part look at the seemingly bipolar ways that extreme eruptions can affect climate (and perhaps, in the past, also cat evolution).

The Quiz

---

Deep in Earth’s mantle, a plume of extra-hot rock rises off the edge of Jason, far below the Pacific Plate, and takes millions of years to ooze its way up to the surface.

When it finally erupts, will the resulting Hawaiian hotspot volcanoes:

• a. Help warm Earth by outgassing greenhouse gasses, particularly CO₂?
• b. Chill things down?
• c. Have no global effect at all?

---

---

Don’t peek!

Okay, it’s a. Kilauea is among the world’s top ten CO₂-producing volcanoes, although its daily output alone isn’t enough to change global climate.

Smaller contributions elsewhere also count — so much so that Earth’s volcanoes, taken together, do regulate natural carbon dioxide levels in our atmosphere. (Fischer et al.)

And since CO₂ is a greenhouse gas, volcanoes help to keep our planet’s surface warm.

Note: I’m intentionally ignoring humanity’s greenhouse gas contribution here, both to highlight natural processes that likely affected cat evolution and because no people were around during the events that these two series cover: the early evolution of animals, cats, and the modern natural world (much of which is built upon Miocene (23 to 5.3 Ma) systems that in turn have deeper roots going back into the Precambrian).

H. sapiens didn’t show up until late in the Pleistocene epoch, just during its last few hundred millennia; Family Felidae, on the other hand (paw?), goes back almost 30 million years, while animals have been evolving for hundreds of millions of years! (Gradstein et al., 2012; Mukherjee et al.; Werdelin et al.)

Getting back to volcanoes, their substantial CO₂ emissions currently more than balance the amount taken out of the air by other global processes (Piombino), including:

• Photosynthesis:
  

  ---

  

  ---

• The ocean
• Plate tectonics
• Mineral weathering.

Those links are for anyone who might be interested in more information about Earth’s carbon cycle.

You don’t need to look them up in order to get the basic idea:

1. Today (and probably all through geological time), lots of natural carbon dioxide comes out of volcanoes. Right now there’s enough of this natural greenhouse gas left over, after planetary processes have taken their share, to warm the planet.
2. If the output from volcanism dropped, or if one of the other Earth systems got stronger — say, a new mountain chain arose, increasing the weathering that removes CO₂ from the atmosphere — then the total amount of this greenhouse gas in our atmosphere would decrease, as would the greenhouse effect, and the planet would cool down.
3. If more and/or bigger eruptions occurred AND the other global processes couldn’t up their game enough to handle the increased CO₂, Earth would warm up.

So fire begets fire, or at least a “warm to hot” setting on the climate thermostat.

---

---

Kilauea, October 2021. Champagne isn’t the only liquid that CO₂ bubbles out of!

---

Ice

I specified Hawaiian volcanoes up there to keep things simple — their eruptions usually aren’t very violent.

At more explosive volcanoes, sometimes fire does beget ice — well, a temporary switch to “cool to cold” settings.

If option b on that quiz looked good, then you might have been thinking of another common volcanic gas: sulfur dioxide. That indeed can lower surface temperatures.

How?

If enough SO₂ is blown into the stratosphere (at least 5 to 10 teragrams, or 5 to 10 million metric tons), it will form a veil of sulfate aerosols that, among other effects, reduces the amount of sunlight reaching the ground. (Oppenheimer)

The violent eruption of an Indonesian volcano in 1257 A.D., for instance, blasted out enough sulfur dioxide to cool the planet, possibly (with help from other big eruptions) all the way into a six-century-long Little Ice Age. (Rathi)

In case you’re wondering about the big blast from Tonga’s volcano on January 15th of this year, experts agree that the column definitely reached the stratosphere, but their satellite measurements show that, fortunately, there wasn’t enough SO₂ in it to affect climate very much.

As is often the case when talking about volcanoes and climate, the connection between big eruptions and the Little Ice Age of the 13th to 19th centuries is complicated by other changes in Earth’s systems that happened around the same time.

Our planet is a sort of machine that makes entropy (whatever that is) (Gan et al.); Earth systems, large and small, work very much like enmeshed gears in that machine.

Change one little thing, and the whole machine responds: in positive ways, negative ways, or (perhaps most often) both. It’s very, very complex.

I think this is one reason why reputable scientists are careful not to claim in their papers, for instance, that large eruptions definitely cause mass extinctions or other major disruptions of Earth’s carefully balanced systems.

There are so many other factors involved.

But they can’t overlook those massive eruptions, any more than a store owner can overlook the sudden appearance of a bull in the fine china aisle: no matter what that shopkeeper does, something valuable is going to get broken. And if conditions are right, the whole shop might get trashed.

Oddly enough, this metaphor carries over to the real world. Sometimes (but not always), enormous eruptions, long since ended but still recorded in stone, appear to have broken the planet’s systems.

Some researchers associate episodes of intense, large-scale volcanism with such catastrophes as Snowball Earth episodes (because of lowered CO₂ from increased weathering of all that lava after the eruption is over) or major mass extinctions from overheating and other effects of a sudden overload of volcanic gases.

Either world-changing fire or global ice, depending on the era, might have been produced, at least in part, by intense volcanism. (I’ll give you a couple of examples in the next post.)

How extreme does an eruption have to be to do that?

Bigger than anything that’s happened here for the last 16 million years or so.

These bullish eruptions, called LIPs (large igneous provinces), do keep occurring — on average, every 30 million years or so (Ernst et al.) — so it’s good to know something about them, in case the next one, wherever it breaks out, jumps the gun a bit.

Large igneous provinces (LIPs)

It’s hard to wrap your mind around the scale of a LIP eruption.

Imagine this —

---

---

Part of Iceland’s largest lava flow in more than three centuries.

---

— but with much more volume and power behind it and with many more flows, each one covering the last in a geological blink of the eye:

---

---

That’s a lot of lava.

How do the physical laws that sometimes bring fire or ice apply to large igneous province eruptions?

We’ll look at that in Part 2.

---

Featured image: Surapong/Shutterstock

---

Sources:

Bryan, S. E., and Ernst, R. E. 2008. Revised definition of large igneous provinces (LIPs). Earth-Science Reviews, 86(1-4): 175-202.

Ernst, R. E.; Bond, D. P.; Zhang, S. H.; Buchan, K. L.; and others. 2021. Large Igneous Province Record Through Time and Implications for Secular Environmental Changes and Geological Time‐Scale Boundaries. Large Igneous Provinces: A Driver of Global Environmental and Biotic Changes, 1-26.

Fischer, T. P.; Arellano, S.; Carn, S.; Aiuppa, A.; and others. 2019. The emissions of CO₂ and other volatiles from the world’s subaerial volcanoes. Scientific Reports, 9(1): 1-11.

Gan, Z.; Yan, Y.; and Qi, Y. 2004. Entropy budget of the earth, atmosphere and ocean system. Progress in Natural Science, 14(12): 1088-1094.

Gradstein, F. M.; Ogg, J. G.; and Hilgen, F. G. 2012. On the geologic time scale. Newsletters on Stratigraphy. 45(2): 171-188.

Keller, G. 2005. Impacts, volcanism and mass extinction: random coincidence or cause and effect?. Australian Journal of Earth Sciences, 52(4-5): 725-757.

McNamara, A. K. 2019. A review of large low shear velocity provinces and ultra low velocity zones. Tectonophysics, 760: 199-220.

Mukherjee, I.; Large, R. R.; Corkrey, R.; and Danyushevsky, L. V. 2018. The Boring Billion, a slingshot for complex life on Earth. Scientific Reports, 8(1): 1-7.

Oppenheimer, C. 2011. Eruptions That Shook the World. Cambridge: Cambridge University Press. Retrieved from https://play.google.com/store/books/details?id=qW1UNwhuhnUC

Palin, R. M., and Santosh, M. 2020. Plate tectonics: What, where, why, and when?. Gondwana Research. (PDF)

Pastor-Galán, D.; Nance, R. D.; Murphy, J. B.; and Spencer, C. J. 2019. Supercontinents: myths, mysteries, and milestones. Geological Society, London, Special Publications, 470(1): 39-64

Piombino, A. 2016. The heavy links between geological events and vascular plants evolution: a brief outline. International Journal of Evolutionary Biology, 2016. (PDF

Rathi, A. 2013. Indonesia’s Samalas volcano may have kickstarted the Little Ice Age. https://arstechnica.com/science/2013/09/indonesias-samalas-volcano-may-have-kickstarted-the-little-ice-age/

Werdelin, L.; Yamaguchi, N.; Johnson, W. E.; and O’Brien, S. J.. 2010. Phylogeny and evolution of cats (Felidae), in Biology and Conservation of Wild Felids, eds. Macdonald, D. W., and Loveridge, A. J., 59-82. Oxford: Oxford University Press.

---

---