The Great Forgetting

It had only snowed a dusting the day before, but my brother Jebsen had gone snowboarding at the local hill anyway. He and his friends had discovered a secret spot behind a small shopping plaza in Saugerties, New York, where they would build jumps on an undeveloped hillside in the woods. The packed piles of snow were more resistant to melting, so all they needed was a thin layer to freshen things up and they would disappear there for the day.

As my mother and I pulled up to the curb to pick him up, I noticed an unusual tiredness hung in his hunched shoulders. He had a dull stare that seemed to barely register our arrival, and his snowboard was sprawled halfway into the parking lot, as if he couldn’t be bothered to tend to it.

Slumping into the back seat, he complained of a headache. It came out a few miles down the road that he had hit his head on a rock and blacked out after going off one of the jumps. He said he wasn’t sure how long he was out for, but when he regained consciousness, he decided to shake it off and keep snowboarding with the guys for the rest of the day.

I could hear my mother’s deep inhalation, her eyes flipping up to assess him in the rearview mirror. “You probably have a concussion,” was her matter-of-fact assessment, masking the sudden tension that had set in. Back then, concussions were viewed as unfortunate but passing injuries, and Jebsen had many previous concussions that seemed to resolve just fine. Rather than view his prior record as a risk factor for more serious brain damage, it was easier to see it as evidence of resilience. “You should take it easy for a few days,” my mother said.

At a stoplight, however, we noticed something different this time. When my mother mentioned events of the previous day, Jebsen didn’t know what she was talking about. I laughed, thinking he was kidding, but when I swung my head back to exchange a smile with him, his face was slackened with confusion.

We volleyed back and forth on the way home, checking the big stuff first—names, people, places—until we homed in on the line that divided his intact memory from the events that had been swept clean: two weeks. The past two weeks of his life had been eroded at a sharp contact, like an underwater turbidity current that sweeps off the topmost sediment as it barrels downslope.

I was relieved that everything important, everything central to his identity, was still intact. On the surface, it seemed a minor loss, an otherwise mundane cache of daily routines. But it would be a lie to omit the unease I felt emanating from that scarp in his memory. It was like a sinkhole that suddenly pockmarks the ground; we rope it off with caution tape and cones, trying to reassure ourselves that the dangers have been safely delineated.

As a paleoclimatologist, my work revolves around the tenet that the past provides context and constraints for better understanding the future. Knowing how much the planet warmed when atmospheric carbon dioxide was as high or higher than it is today provides insight into the possible future trajectories of climate under rising greenhouse gases.¹

Earth records provide us with this information: Ice cores, tree rings, ocean sediments, stalactites and stalagmites in caves, growth rings in corals, tusks, and mollusks. These archives accrete memories on time periods varying from months to millions of years, allowing us to see a spectrum of Earth changes on various temporal and spatial scales—how biology, ocean, and ice respond to climate change in signature patterns, and the points at which those systems are pushed past thresholds.

How does a billion years of Earth’s history go missing?

This is one of the most important insights that paleoclimate archives provide: They show us how the real world breaks. How resilience folds into catastrophic failure. They show us the edges and asymmetries of the climate system: the thresholds of tolerance in ecological networks; the slow steady slog of diversification and the quick ax of extinction; the long timescales it takes for ice sheets to grow—accumulating million-year memories—and how fast they can melt, puddling history into storm surges that erode the banks of our futures.

As I watch the unfolding of extreme events across our planet, I find myself continuously relocated to that moment in the car with my brother. The sense of fracturing that ripples from a single shock event, even if the full extent of damage is yet to reveal itself.

We didn’t go to the hospital that day after my brother’s snowboarding accident. We went home instead. My mother cooked dinner. Jebsen retreated to his room to lie down. But from that point on, he continued to retreat farther and farther from us.

The signs were subtle at first. He lost weight. He became more withdrawn, more angry about the world’s injustices, but it was hard to tease out what was the normal moodiness of a teenager and what veered off into stranger territory. He had been reading Krishnamurti at the time, and he seemed to take on the mantle of an ascetic—most acutely with food and eating, which he suddenly viewed as a grotesque act of consumption. I tried to be an ally, but everything I did was wrong—the simple act of eating dinner disgusted him.

One day, I came into the kitchen and saw him pouring orange juice onto our potted orange tree. When I asked what he was doing, he told me the tree would grow better if given more of the nutrients it needed to produce its fruit. “I don’t know if that’s how it works,” I said, a younger sister still afraid to contradict her older brother. “It might not be good for the soil.” He looked at me for a long time from across the room, more in pity than rebuff, and I could feel his eyes starting to perceive me as an outsider instead of a sibling who had shared the same chaotic upbringing.

On weekends, the two of us would still go to the junkyard where we grew up to work odd jobs for my father. But Jebsen became increasingly unreliable, unfocused, and when my father found him huffing gasoline one day, he kicked him off the junkyard and told him he wasn’t allowed back until he got his act together. My father thought it would shock the sense back into him, but for Jebsen it severed a touchstone of his identity.

As kids, the two of us were often left to navigate the treacherous, lost world realms of the junkyard together—acres of vine-encrusted carapaces of old cars, broken school buses, and rotting wooden ships, all scattered around the swamp and bluestone cliffs that ran through our property in upstate New York. We pillaged for presents for my mother in trunks of cars and burned-out trailers. We skated the swamp in winter, shoveling labyrinthine paths around the trees and root islands. We pretended to drive the crumpled convertibles and sail the ships that slowly filled with the soil of fallen leaves. As hostile a place it may have seemed to outsiders, to us the junkyard was an island of consistency, a comforting place with the aging faces of the cars that had stood watch over our childhoods. To be banished from the junkyard was to send my brother out to sea.

In geology, an “unconformity” represents an aberration in the normal accumulation of sediment, a glitch in the record-keeping of Earth’s history. “A stratum of amnesia in the geological record, where overlying rock, significantly younger than what lies below, represents some break in an otherwise continuous story of formation,” is how writer and poet Kim Stafford defined it.²

The longest lacuna in Earth’s history is known as the Great Unconformity. It represents a temporal gap ranging from a hundred million years to over a billion years, depending on the location. It’s visible in the Grand Canyon as the boundary between the Precambrian Vishnu Schist and the Cambrian Tapeats Sandstone, between which there is a billion years of missing time between about 1,600 and 600 million years ago. Looking at this line in the strata, it is hard to fathom all that would have conspired across that vast gulf of time, for which there is simply nothing. If it were instead to have been the last billion years that was erased, it would obliterate the entire history of complex life. No trace of a single animal having ever walked the land. No dinosaurs, no whales, no humans, no pyramids.

How does a billion years go missing? The Great Unconformity has long been a geological mystery, in no small part because it is a challenge to reconstruct history when records of history are missing.

He left, disappearing into the autumn chill without so much as a warm jacket.

It turns out, ice sheets are good shredders. Recent research³ suggests that the Great Unconformity may be a result of Snowball Earth—when the planet descended into deep cold (about 700 million years ago), and glaciers covered most of the land. A billion years of history was ground down by ice and bulldozed into the seafloor, where it was subducted into the Earth’s mantle and recycled into magma, ready to be remade into new history—albeit with a few hidden remnants of the past stored safely away in subterranean crystals.⁴

While the erosive action of ice sheets may have been responsible for the largest unconformity in the Earth’s lithosphere, ice sheets themselves are some of the best memory banks on our planet. Greenland stores over 100,000 years of history. Antarctica stores over a million. These ice sheets are written by the daily weather, each snowstorm condensed into the jagged rhythms of ice age cycles that steadily build into mile-high mountains—the great brains of our planet, perched on the poles.

Ice sheets can recall the large volcanic eruptions that occurred throughout their lifetimes and the turn of the weather those years. Antarctica remembers the levels of carbon dioxide in the atmosphere 800,000 years ago and its natural variations since—the consistently bounded maximums and minimums of glacial and interglacial cycles,⁵ and the harrowing departure from those bounds in recent decades.⁶ Greenland remembers when Romans started smelting silver, as the toxic lead dust settled over the ice; it knows too when Rome fell, from the cessation of this dust.⁷ Information is best preserved on ice.

But the world’s glaciers are now hemorrhaging their histories. Mountain glaciers are peeling at their edges like smoldering paper, while Greenland sweats off a million tons a minute.⁸ On bad days, it is enough water to submerge entire states.⁹ Between 1994 and 2017, 30 trillion tons of ice have been lost globally,¹⁰ and things are just starting to heat up. In August of 2021, it rained on the summit of Greenland. A melt layer will form to mark the event—a dire sign for the top of an ice sheet. Coastal areas along Greenland have become too slushy to drill into, preventing scientists from retrieving ice cores in those regions, rendering its history inaccessible.¹¹

Antarctica has been the slowest beast to awaken, but the icy tentacles that reach out to moor the giant are starting to slip. These floating ice shelves extend out from where the ice sheet is grounded to the bedrock, helping to stabilize the interior, but now they are starting to weaken from the forces of ocean warming and rising seas. As the ice shelves disintegrate into the ocean, the ice upstream accelerates its descent, increasing sea level.

In 2022, double heat waves hit the Arctic and Antarctic, temperatures soaring close to 40 degrees Celsius higher than usual. The Conger ice shelf in East Antarctica said its final farewell following this heat wave. West Antarctica has long been considered the more vulnerable to near-term ice shelf loss, but now, even the East is starting to show its fray. Heat makes easy work of forgetting.

Months went by as my brother’s condition continued to deteriorate, but all attempts to get him to see a doctor had failed. When he turned 18, my mother couldn’t force him to go despite her efforts. Emaciated from self-starvation, his head bent over, he looked like a ghost of his former self. Any attempts to nudge him toward help were met with slammed doors and further retreat.

As I came back home one day from a hike in the woods, I noticed a wall of blackberries covering an old fence at the campground next to our property. I remember the distinct feeling of hope I had at the sight of them, the momentary illusion of a solution. I thought Jebsen would gladly eat the berries because they were wild and didn’t cost anything, so I hurried home and got a colander to collect them.

I wanted to believe in the limitlessness of resilience.

I knocked on his bedroom door, my colander full to the brim of blackberries. “Look what I found across the street,” I said, holding out the berries as a peace offering. He looked up at me and met my eyes for the first time in months. “What will the birds eat?” he asked, searching for my decency. So I took the colander full of berries and flung them back outside, along with my hopes of him getting better.

By autumn, my mother gave him an ultimatum: Go to the doctor or move out of the house. He left instead, disappearing into the autumn chill without so much as a warm jacket. A few weeks later, my mother found him living in our uninsulated outdoor basement. He had been sleeping on the ground next to the water heater, surrounded by mouse traps. She took him back in, thankful he was alive.

We hobbled along for a few more months, in the limbo of knowing something had to give. Finally, one night my mother told me, “It’s going to happen tomorrow. Uncle Bill is coming. And dad. The police will come.” When I got off the school bus that day, Jebsen wasn’t home. He had been committed to a psychiatric hospital. I asked my mother what happened, but she just shook her head. “They had to restrain him,” was all she said. In the following days, he was diagnosed with schizophrenia.

In the biosphere, resilience is deeply entwined with memory—it is the ability of a system to find its way back to an equilibrium state following a perturbation, which requires memory of previous states. For example, ecological memory in forest ecosystems can be thought of as containing “information and material legacies” that map out adaptive strategies to disturbances such as fire, drought, or temperature changes.¹² Material legacies include seeds that sprout after a fire and dead logs that become home to plants and fungi.

Material legacies, however, can be lost or diminished as environmental conditions change. Often those changes are driven by humans, such as the extinction of species or the introduction of invasive ones. Those changes can generate a “resilience debt,” the reduced capacity of a system to recover. That debt, though, is apparent only after an ecosystem is disturbed. Given that ecosystems naturally respond slowly to environmental changes, from decades to centuries, those changes to observers may be mistaken for resilience, making it difficult to predict future responses to new perturbations.

The importance of memory isn’t just in the information it contains. In the Earth System, components with large memories act as buffers to short-term variability. They are a form of inertia, slowing the initial response to a perturbation. Oceans absorb atmospheric heat and carbon dioxide; forests cool their environments through carbon uptake and evapotranspiration, a process that transfers water back into the atmosphere and helps to stabilize the hydrological cycle.¹³ Ice sheets keep the planet cool through their high albedo, a measurement of how much light is reflected by their surface. As the ice sheets melt, more solar radiation is absorbed by Earth, driving up temperatures and increasing melting in a positive feedback.

But the complexity of memory is also what sets it up for failure when it is pushed past its limits. The same structure that can stabilize in the face of small perturbations, can topple catastrophically when the rates and magnitudes of change become too great.

Before a tipping point in a complex system, there are early warning signals that may be detected.¹⁴ The most widely applicable of these early warning signals is “critical slowing down”—the phenomenon we are all familiar with before our computer crashes, and rather than heed the implications of this slower processing power, we jam at the keys in frustration, doubling down on our demands until the computer blacks out. These are the times information is most likely to be lost if it hasn’t been secured in long-term storage.

Critical slowing down indicates the system is losing its ability to attain its previous equilibrium and is instead becoming attracted or pulled into an alternate state. It is a loss of resilience, a loss of the negative feedbacks that help keep a system rooted in stability. Various subsystems that are sensitive to thresholds—such as the Amazon rainforest—are already showing signs of critical slowing down.¹⁵

Given the complexity of the Earth System, it is hard to fathom the extent of information loss currently underway. There are, however, attempts to quantify the memory loss in the Earth System.

In one model, where anthropogenic CO₂ emissions are the stressor, and the strain on the system is the ability of the land and ocean to sequester carbon, researchers show the latter is inherently slower than the former. They estimate that 60 percent of Earth’s memory had already been degraded by 1959, and that the ability for Earth to build-up memory has been impaired, reducing its capacity to respond to stresses within its natural stress-strain regime.¹⁶ Estimates of persistence in this model—akin to critical slowing down—are increasing, signaling a departure from the bounds of Earth’s natural regime well before 2050, if the stressors of rising atmospheric carbon dioxide continue their current trajectory. The ocean is undergoing memory loss too, increasing variability and reducing predictability of future temperature patterns.¹⁷

The intractable problem we face is the asymmetry of timescales: It takes time to build memory, but it can be erased in a geological instant. Like so many things we take for granted, it is difficult to see these stabilizing forces until they are gone. As we untether the anchors of the past, the future becomes unmoored.

Jebsen’s health and memory continued to deteriorate. During one low point, he stopped taking his medications and was kicked out of the house where he had been living. For weeks he was homeless, somewhere in the woods of Phoenicia, not answering calls. When he resurfaced, my cousin, aunts, uncles, and half-brothers pooled resources to put him up in a motel. I was on the West Coast, with a young child, unable to visit often. But we talked on the phone regularly. I could hear in his voice that his health was worsening, but he made me promise not to get the doctors involved anymore.

Every time we talked, he would recount the same few stories, as if everything else had been whittled away, leaving only the unerodable core of his memories. Most were from the early days, the junkyard days. Many involved some sort of peril—the time I got stuck in my father’s van, rolling backward down our driveway as Jebsen ran alongside, urging me to jump out the window, or the time my father’s finger got sliced off by a falling car window and he asked Jebsen to go get some paper towels from the house. He would end the story by saying, “Uh, Dad, I think you’re going to need more than paper towels,” and we would both laugh.

A few months before his 39th birthday, Jebsen died of cirrhosis.

The bounds of Earth’s memory are being severely tested. Biodiversity is in stark decline.¹⁸ Complex ecosystems that contain libraries of genetic information—potential medicine cabinets for ailments yet unleashed—are being degraded into monocrops. Rates of extinction in recent decades are 10 to 100 times greater than the last 10 million years and over 1 million species face extinction in the coming decades. Extinction represents the ultimate memory loss: an end of the line for information that had been continuously transcribed in the Earth’s living library for hundreds of millions of years.

Wildfires are razing ancient forests and entire towns—thousand-year histories contained in towering redwoods mixed with decades of human history, billowing in pyrocumulous clouds that puncture the stratosphere like volcanic eruptions. These charred landscapes are everywhere in California: Burn scars reach from the Santa Cruz Mountains to the ocean. The ridges of northern Sonoma look like a shaved dog’s back of bristled matchsticks. Crows perch in black snaggle Manzanita. Charcoal limbs are scattered at broken bone angles through the Echo Summit pass, the only evidence of the houses that once stood are the stone chimneys standing in ashes, like ancient cairns in abandoned landscapes.

Everywhere on Earth, amnesia is smoldering. Ash from our most ancient libraries is raining down on us, lofted into toxic smoke that circles the globe, darkening glaciers that accelerate their melting, sending thousands of years of history pouring into the ocean, where it steadily rises up to erode the banks of our futures. Those who can’t shake the shivers of ill ease are the ones who have always sought wisdom from the past, and suddenly there is an eerie silence—stumps of history, no longer talking back.

While I can never know whether the snowboarding accident was directly linked to Jebsen’s schizophrenia, when I think back to the tragic turn of his trajectory, I fixate on that moment in the car when he first showed signs of amnesia. I fixate on our immobility; on the lack of actions we took to assess the larger damages that may have been hiding beneath that hole in his memory. It wasn’t for lack of concern, but a lack of money that kept us away from hospitals, and an excess of momentum that kept us rutted in the daily grind. I plead with my former self to encourage my mother to take him to the hospital. I even imagine that I am the source of ill ease I felt that day, peering back at my past with such unforgiving that I have burned a hole straight through spacetime.

Even if we couldn’t have changed the outcome, we would have tried, and maybe we would have been more prepared for what was to come. We wouldn’t have ignored the troubling signs that were easy to overlook in their progressive slippage, until one day, he was skin and bones, hunched and mumbling, unable to look me in the eye, and all I could ask myself was: How could I not have seen it all unfolding? The answer is that I did see it, but I wanted those warning signs to be aberrations; I wanted to believe in the limitlessness of resilience.

Near the end of Jebsen’s life, he shared one memory that was different from all the other stories he normally retold. It was about a road trip from Oregon to Northern California with my mother and me—the only time he ventured west. We were headed to Mt. Shasta but made a diversion to Humboldt Redwoods State Park to see the giant trees. What I remember from that day was how quiet Jebsen was, and I assumed he was anxious from the challenges of traveling.

But in one of our final conversations, he recounted vivid details of driving through the Avenue of Giants, the tallest trees in the world. I was surprised by the clarity of this memory and mentioned how I had interpreted his silence as disinterest at the time. He corrected me, saying, “No, those trees were just the most amazing things I’d ever seen in my life.”

Summer Praetorius is a paleoclimatologist who uses ocean sediment records and marine microfossils to reconstruct past changes in ocean circulation and climate. Her work focuses on understanding the causes and effects of abrupt climate change in the Northern Hemisphere, with a focus on the Pacific Ocean.

Lead illustration by Katherine Streeter.

References

1. Tierney, J., et al. Past climates inform our future. Science 370 (2020).

2. Stafford, K. in Lopez, B.H. & Gwartney, D. (Eds.) Home Ground: Language for an American Landscape Trinity University Press, San Antonio, TX (2006).

3. Keller, C.B., et al. Neoproterozoic glacial origin of the Great Unconformity. Proceedings of the National Academy of Sciences 116, 1136-1145 (2019).

4. McDannell, K.T., Keller, C.B., Guenthner, W.R., Zeitler, P.K., & Shuster, D.L. Thermochronologic constraints on the origin of the Great Unconformity. Proceedings of the National Academy of Sciences 119, e2118682119 (2022). 

5. Luthi, D., et al. High-resolution carbon dioxide concentration record 650,000–800,000  years before present. Nature 453, 379-382 (2008).

6. NOAA Mauna Loa CO2 Record: https://gml.noaa.gov/ccgg/trends/

Full CO₂ record: https://climate.nasa.gov/climate_resources/24/graphic-the-relentless-rise-of-carbon-dioxide/

7. McConnell, J., et al. Lead pollution recorded in Greenland ice indicates European emissions tracked plagues, wars, and imperial expansion during antiquity. Proceedings of the National Academy of Sciences 115, 5726-5731 (2018).

8. Carrington, D. The Greenland ice sheet lost a record 1m tonnes of ice per minute. The Guardian (2020).

9. Milman, O. Greenland: Enough ice melted on single day to cover Florida in two inches of water. The Guardian (2021).

10. Slater, T., et al. Review article: Earth’s ice imbalance. The Cryosphere 15, 233–246 (2021).

11. Garrison, C., Baldwin, C., & Hernandez, M. Scientists scramble to harvest ice cores as glaciers melt. Reuters (2021).

12. Johnstone, J.F., et al. Changing disturbance regimes, ecological memory, and forest resilience. Frontiers in Ecology and the Environment 14, 369–378 (2016).

13. Makarieva, A.M., et al. Vegetation impact on atmospheric moisture transport under increasing land-ocean temperature contrasts. Heliyon 8, e11173 (2022).

14. Scheffer M., et al. Early-warning signals for critical transitions. Nature 461, 53–59 (2009).

15. Boulton, C.A., Lenton, T.M., & Boers, N. Pronounced loss of Amazon rainforest resilience since the early 2000s. Nature Climate Change 12, 271-278 (2022).

16. Jonas, M., Bun, R., Ryzha, I., & Zebrowski, P. Quantifying memory and persistence in the atmosphere-land and ocean carbon system. Earth System Dynamics 13, 439-455 (2022).

17. Shi, H., et al. Global decline in ocean memory over the 21st century. Science Advances 8, eabm3468 (2022).

18. Diaz, S., et al. Summary for policymakers of the global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. IPBES.net (2019).

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