Meltdown

One of the most frustrating things about human behavior is that we can receive repeated hints and warnings that if we keep doing what we're doing, bad stuff will happen, then when we continue and bad stuff does indeed happen as predicted, we act all surprised.

We've seen it before with volcanic eruptions, a topic I just dealt with in more detail last week.  As I pointed out, it's impossible (as science currently stands) to predict exactly when volcanoes will erupt, and sometimes they still take us completely by surprise, such as the May 2021 eruption of Mount Nyiragongo in the Democratic Republic of Congo.  But a much better-known example of an eruption geologists saw coming was the March 1980 eruption of Mount Saint Helens, which killed 57 people, a significant fraction of whom were leisure hikers hoping to get close to the mountain, some of whom deliberately went around signs and barricades warning of the danger.

There's something in human nature that makes us say, "Oh, c'mon, that sign isn't meant for me.  We'll be fine."

Which is why we're now in the position of being presented with a study from the University of South Florida confirming what climatologists have been saying for decades -- that anthropogenic climate change, generated by the burning of fossil fuels, is going to melt the on-land ice masses in Antarctica and Greenland, and produce catastrophic sea level rise.

The first person who connected atmospheric carbon dioxide levels with global average temperature was, I shit you not, the Swedish chemist Svante Arrhenius, 126 years ago.  That's how long we've known about this.  It started being the subject of serious study (and concern) in the 1970s, and in the 80s and 90s popularizers such as James Burke and Al Gore brought it to the public notice with (respectively) After the Warming and An Inconvenient Truth.  But it's easy to ignore people if paying attention to them means having to change your lifestyle; easier to listen to knuckle-draggers like Oklahoma Senator James Inhofe, who famously brought a snowball onto the floor of the Senate as "proof" that the world wasn't warming up.

Unfortunately for Senator Inhofe, nature continues to operate by the laws of physics and not the financial interests of the fossil fuel industry, because the temperature has continued to climb.  And just last week, a new study in Nature has shown that the Thwaites Glacier in Antarctica has lost contact with the rocky basin it rests on, and is in the process of collapse -- something that could raise global sea levels by three meters.

"Thwaites is really holding on today by its fingernails," said marine geophysicist and study co-author Robert Larter from the British Antarctic Survey.  "We should expect to see big changes over small timescales in the future -- even from one year to the next -- once the glacier retreats beyond a shallow ridge in its bed."

If that doesn't drive the point home hard enough, the authors point out that according to the United Nations, roughly forty percent of the human population lives within a hundred kilometers of the coast.

The edge of Thwaites Glacier [Image is in the Public Domain courtesy of NASA]

I feel like the climatologists, and also science writers like myself, have been jumping up and down yelling ourselves hoarse for years trying to get people to wake up, and for God's sake, do something.  But the USF study is the most recent indication that whatever window we had to mitigate the effects of human-induced climate change might well have closed.  I hate to be a doom-and-gloom purveyor, and I wish I had good news; but at the moment, this is what we have.  We've allowed people like Senator Inhofe and their mouthpieces over at Fox News to convince the public that somehow we climate activists want bad things to happen, so we're exaggerating them for our own malign purposes.  And all the while, the voters have been climbing over the signs saying "Danger, Do Not Proceed Past This Point," saying, "Ha ha, this can't be meant for me."

I'm very much afraid that the result is we're in the latter half of "Fuck around and find out."

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Caught in the sea's net

The specter of climate change is getting difficult to ignore.  While you still can't point at a particular event and say "that happened because of anthropogenic climate change" -- as I said about a million times to my students, "climate isn't the same as weather" -- we've had enough anomalous heat waves, droughts, floods, and storms in the past ten years that it's getting harder and harder to deny unless you go around with blinders on or are just plain stupid.  (The latest being the catastrophic tornadoes that tore through Kentucky a couple of weeks ago, despite it being December, usually a low point in tornado occurrence and intensity.)

There are signs that even the science deniers are beginning to have some traces of second thoughts about the whole thing.  A study in Nature Scientific Reports a few weeks ago found that "climate contrarians" have of late begun to shift their ground, from outright denial that it's happening to attacking the researchers' integrities and the solutions they propose.  While this is still maddening to those of us who can actually read and understand a scientific paper, it's at least a tentative step in the right direction.  "I don't like the people who are saying this" and "the solutions won't work/are too expensive" are better than "this isn't happening" and "la la la la la la la not listening."

But the evidence that the situation is perilous keeps piling up.  One of the consequences of climate change most people don't think a lot about is sea level rise, mostly because the numbers seem insignificant; for example, a recent study showed that in the twenty-seven years between 1993 and 2020, the average sea level rose by a centimeter, and the rate of rise in the past ten years is triple what it was in the twentieth century.

It's easy to say, "a centimeter?  That's hardly anything."  But that ignores a couple of things.  First, that's an average; because of patterns of melt water, and sea and wind currents, some places have seen an increase of up to twenty centimeters, easily enough to cause devastating coastal flooding and infiltration of fresh-water aquifers with salt.  Second, there's geological evidence that when the sea level rises, it can happen in fits-and-starts, as ice shelves (primarily in Greenland and Antarctica) collapse.  Given how many people live in low-lying coastal areas, it wouldn't take much to cause a humanitarian catastrophe.

Another pair of studies that came out just last week have illustrated how vulnerable coastal communities have been -- and still are -- to changes in sea level.  Archaeologists uncovered evidence from two millennia ago in southern Brazil indicating that a drop in sea level due to increases in polar ice exposed shellfish beds that the coastal indigenous people depended on, and led to wide abandonment of settlements in the area.  The opposite happened in Greenland in the fourteenth century -- coastal communities that had been settled by Vikings three centuries earlier got swamped, eradicating coastline and driving the settlers up against uninhabitable glacial regions.  They were caught between the rising seas and the rising ice, trapped in an ever-shrinking strip of land that eventually disappeared completely.

[Image licensed under the Creative Commons Jensbn, Greenland scenery, CC BY-SA 3.0]

My initial reaction to the latter paper was puzzlement; the fourteenth century was the height of the Little Ice Age, so you'd think the freeze-up would have lowered sea level, not raised it.  But I was failing to take into account isostasy, which is the phenomenon caused by the fact that the continents are literally floating in the magma of the mantle.  Just like adding weight to a boat causes it to ride lower in the water, adding weight to a continent causes it to sink a little into the mantle.  So when the ice sheets built up on Greenland, it pushed it downward, submerging habitable coastline.  (The opposite has happened as the glaciers have melted; in fact, it's still happening in Scandinavia, Canada, and Scotland, the latter of which is still undergoing isostatic rebound at a rate of ten centimeters of uplift per century.)

The deniers are right about one thing; the Earth has certainly experienced climatic ups and downs throughout its long history.  What's terrifying right now is the rate at which it's happening.  A study from the International Panel on Climate Change found persuasive evidence that the rate of temperature increase we're seeing is higher than it's been since the Paleocene-Eocene Thermal Maximum, over fifty million years ago.

If that doesn't scare you, I don't know what would.

It's the humanitarian cost that's been on my mind lately, not just because of today's climate change, but the changes that have occurred historically.  I was so captivated by the tragedy of the disappearance of the Norse settlements in Greenland that years ago, it inspired me to write a poem -- one of the few I've ever written.  What would it be like to be the last person alive in a place, knowing no one would come to rescue you?  I can only hope humanity's fate won't be so bleak -- but whenever I think about our reckless attitude toward the environment, this haunting image comes to mind, and I thought it would be a fitting way to end this post.

Greenland Colony 1375

He goes down to the sea each day and walks the shore.
Each day the gray sea ice is closer, and fewer gulls come.
He wanders up toward the village, past the empty and ruined rectory.
The churchyard behind it has stone cairns.  His wife lies beneath one,
And there is one for Thórvald, his son,
Though Thórvald's bones do not rest there; he and three others
Were gathered ten years ago in the sea's net
And came not home.

Since building his son's cairn,
He had buried one by one the last four villagers.
Each time he prayed in the in the stone church on Sunday
That he would be next,
And not left alone to watch the ice closing in.

In his father's time ships had come.  The last one came
Fifty years ago.
Storms and ice made it easy for captains to forget
The village existed.  For a time he prayed each Sunday
For a ship to come and take him to Iceland or Norway or anywhere.
None came.  Ship-prayers died with the last villager,
Three years ago.  He still prayed in the stone church on Sunday,
For other things; until last winter,
When the church roof collapsed in a storm.
The next Sunday he stayed home and prayed for other things there.

Now even the gulls are going,
Riding the thin winds to other shores.  Soon they will all be gone.
He will walk the shore, looking out to sea for ships that will never come,
And see only the gray sea ice, closer each day.

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I remember when I first learned about the tragedy of how much classical literature has been lost.  Take, for example, Sophocles, which anyone who's taken a college lit class probably knows because of his plays Oedipus Rex, Antigone, and Oedipus at Colonus.  He was the author of at least 120 plays, of which only seven have survived.  While we consider him to be one of the most brilliant ancient Greek playwrights, we don't even have ten percent of the literature he wrote.  As Carl Sagan put it, it's as if all we had of Shakespeare was Timon of Athens, The Merry Wives of Windsor, and Cymbeline, and were judging his talent based upon that.

The same is true of just about every classical Greek and Roman writer.  Little to nothing of their work survives; some are only known because of references to their writing in other authors.  Some of what we do have was saved by fortunate chance; this is the subject of Stephen Greenblatt's wonderful book The Swerve, which is about how a fifteenth-century book collector, Poggio Bracciolini, discovered in a monastic library what might well have been the sole remaining copy of Lucretius's masterwork De Rerum Natura (On the Nature of Things), which was one of the first pieces of writing to take seriously Democritus's idea that all matter is made of atoms.

The Swerve looks at the history of Lucretius's work (and its origin in the philosophy of Epicurus) and the monastic tradition that allowed it to survive, as well as Poggio's own life and times and how his discovery altered the course of our pursuit of natural history.  (This is the "swerve" referenced in the title.)  It's a fascinating read for anyone who enjoys history or science (or the history of science).  His writing is clear, lucid, and quick-paced, about as far from the stereotype of historical writing being dry and boring as you could get.  You definitely need to put this one on your to-read list.

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The stranded lagoon

When someone talks about getting a glimpse of prehistory from the modern landscape, usually what they're referring to is either (1) rocks, or (2) fossils.

There's no doubt that those are our best clues.  I saw a good example of this last weekend while we were visiting some friends in the Catskill Mountains.  We'd gone for a hike alongside the beautiful tumbling West Kill Creek, and I saw the unmistakable polished surface and parallel grooves of a slickenside -- a rock that had been carved and worn smooth by the passage of a glacier, probably the one that last covered this entire region on the order of twenty thousand years ago. 

Further back -- much further back -- the flaky, flat layers of gray shale and tan limestone that forms the majority of the bedrock around here is Devonian in age, something like three hundred million years old, when where I now sit was at the bottom of a shallow tropical ocean.  Those sediments were uplifted during the formation of the Appalachian Mountain range and have been slowly eroding ever since, with the outflow from the melting glaciers -- the same ones that left the scratches in the rocks I saw in the Catskills -- cutting the deep, steep-sided gorges this region is famous for.

Taughannock Falls -- right up the road from where I live

It turns out, though, that inferences about the past don't just come from rocks and fossils.  A much rarer, but even cooler, phenomenon comes from biology; it's called a relict population or peripheral isolate -- a cluster of individuals of a species left behind and/or cut off from the rest of the population by some major geological event.  An especially interesting one was just discovered recently, and was the subject of a paper in Proceedings of the National Academy of Sciences just published yesterday.  It concerns a clump of red mangrove trees (Rhizophora mangle) along the banks of the San Pedro Mártir River in the Yucatan Peninsula.  What tipped off the researchers that this was something weird was that red mangroves usually only grow in the brackish or salty shallows of tropical ocean shores -- and this one was 170 kilometers inland from the nearest mangrove marshes, along the banks of a freshwater river, with no individuals of that species in between.

Apparently what happened is that these mangroves were left behind after a warm period of high sea level ended.  As the temperature cooled and more ocean water was locked up in the form of ice, the seas receded, cutting off the little clump of mangroves from their cousins.

The authors write:

Climatic oscillations during the Pleistocene played a major role in shaping the spatial distribution and demographic dynamics of Earth's biota, including our own species.  The Last Interglacial (LIG) or Eemian Period (ca. 130 to 115 thousand years B.P.) was particularly influential because this period of peak warmth led to the retreat of all ice sheets with concomitant changes in global sea level.  The impact of these strong environmental changes on the spatial distribution of marine and terrestrial ecosystems was severe as revealed by fossil data and paleogeographic modeling.  Here, we report the occurrence of an extant, inland mangrove ecosystem and demonstrate that it is a relict of the LIG.  This ecosystem is currently confined to the banks of the freshwater San Pedro Mártir River in the interior of the Mexico–Guatemala El Petén rainforests, 170 km away from the nearest ocean coast but showing the plant composition and physiognomy typical of a coastal lagoon ecosystem.  Integrating genomic, geologic, and floristic data with sea level modeling, we present evidence that this inland ecosystem reached its current location during the LIG and has persisted there in isolation ever since the oceans receded during the Wisconsin glaciation.  Our study provides a snapshot of the Pleistocene peak warmth and reveals biotic evidence that sea levels substantially influenced landscapes and species ranges in the tropics during this period.

"This discovery is extraordinary," said biologist Felipe Zapata, of the University of California - Los Angeles, who co-authored the paper.  "Not only are the red mangroves here with their origins printed in their DNA, but the whole coastal lagoon ecosystem of the last interglacial has found refuge here."

 It's fascinating that you can use the distribution of a modern species to infer the conditions hundreds of thousands of years ago -- and, conversely, that the prehistoric climate and geology have left a distinct fingerprint on our current ecosystems.  It makes me wonder what the scientists of the far-distant future will be able to figure out about our world.  One of the ways that humans have changed things the most is the introduction of exotic species; in my part of the world, noxious pests like garlic mustard and Japanese beetles come to mind, but it bears mention that pigeons, dogs, cats, and horses are all introductions to North America that have established feral populations, as are most of the commonly consumed fruits (apples, peaches, pears, apricots, blackberries, raspberries, cherries, and all the citrus fruits), clover, dandelions, barberry, and just about all the species of grass you'd find in your lawn.

I wonder if future biologists will figure out how House Sparrows (Passer domesticus) got here, when their nearest relatives are all the way across the Atlantic Ocean.

The Earth, of course, is not done changing.  Even apart from what we're currently doing to the climate, there is the natural process of plate tectonics moving the continents around, altering patterns of ocean and air circulation with inevitable effects on the living ecosystems.  Piecing together what happened in the past can be done by looking at the present -- especially when you find a clump of trees that "shouldn't be there."

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During the first three centuries C.E., something remarkable happened; Rome went from a superpower, controlling much of Europe, the Middle East, and North Africa, to being a pair of weak, unstable fragments -- the Western and Eastern Roman Empires --torn by strife and internal squabbles, beset by invasions, with leaders for whom assassination was the most likely way to die.  (The year 238 C.E. is called "the year of six emperors" -- four were killed by their own guards, one hanged himself to avoid the same fate, and one died in battle.)

How could something like this happen?  The standard answer has usually been "the barbarians," groups such as the Goths, Vandals, Franks, Alans, and Huns who whittled away at the territory until there wasn't much left.  They played a role, there is no doubt of that; the Goths under their powerful leader Alaric actually sacked the city of Rome itself in the year 410.  But like with most historical events, the true answer is more complex -- and far more interesting.  In How Rome Fell, historian Adrian Goldsworthy shows how a variety of factors, including a succession of weak leaders, the growing power of the Roman army, and repeated epidemics took a nation that was thriving under emperors like Vespasian and Hadrian, finally descending into the chaos of the Dark Ages.  

If you're a student of early history, you should read Goldsworthy's book.  It's fascinating -- and sobering -- to see how hard it is to maintain order in a society, and how easy it is to lose it.

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