This is part of a re-release of The Acceleration, a series that offers a grounded view of climate change. I’m re-releasing because I think I can do better than that first effort. Here it is:
The Earth’s climate has always changed. This is not a controversial statement. It is geology. Our planet has been, at times, a hothouse with crocodiles basking in Arctic waters and palm forests growing across Antarctica. It has also been a world of ice so extreme that geologists still argue about what, exactly, it looked like -- and that argument is worth a moment, because it illustrates how dramatic the range of Earth’s climate history actually is.
Roughly 700 million years ago, during what geologists call the Neoproterozoic glaciations, the planet entered a cold period so severe that ice extended from the poles to at or near the equator. One hypothesis, originally proposed by geologist Joseph Kirschvink in 1992 and developed by Paul Hoffman and Daniel Schrag, holds that this produced a true “Snowball Earth” -- the entire ocean surface sealed under ice kilometers thick, even in the tropics. Under this model, the planet essentially became a frozen sphere, and only volcanic carbon dioxide accumulating in an atmosphere cut off from the ocean’s carbon-absorbing chemistry could eventually produce enough greenhouse warming to break the ice. The mechanism that saved the planet from permanent freeze was, in this reading, the same mechanism now warming it: Carbon dioxide building up faster than the system could process it.
A competing hypothesis, sometimes called “Slushball Earth,” argues that a band of open or slush-covered water persisted near the equator, kept liquid by the physics of tropical solar input. Under this model, photosynthetic life would have survived in these open waters rather than retreating entirely to hydrothermal vents and other refugia, which helps explain how complex multicellular life emerged relatively quickly after the glaciations ended.
What both hypotheses agree on is the essential point: Global temperatures were low enough to produce ice cover across latitudes where we now find rainforest. And life survived it. The planet has been through conditions so extreme that our current climate -- the one we treat as normal, as the way things are supposed to be -- registers as a mild afternoon in the context of deep time.
Since those ancient glaciations, vast ice sheets have advanced and retreated across continents dozens of times. Sea levels have risen and fallen by over a hundred meters. The rock record -- ice cores, ocean sediment layers, isotope ratios in ancient shells and limestone -- documents these swings in detail that improves with every decade of research. The Earth’s climate is not a stable system that humans are disrupting. It is a system that has never been stable. There is nothing special, essential, or ordained about its current state. It is simply what we are used to -- and that, as we will see, is exactly why it matters so much to us.
The conversation about climate has become frustrating because it focuses on the wrong question. We argue endlessly about whether change is happening, when change is the only constant our planet’s history demonstrates. We debate whether humans are “causing” climate change, as though the alternative is a stable baseline we are disrupting -- when no such baseline has ever existed. The political argument absorbs all the oxygen: Is the thermostat moving? Whose fault is it? What should we do about it? But the thermostat has never stopped moving for a single geological instant in 4.6 billion years. The question that actually matters -- the one that determines whether this particular episode of change is dangerous or manageable -- is not whether the climate is changing.
The question is how fast.
I’m Allen Schyf. This is the first episode of The Acceleration -- a series about climate, outside the cultural argument that has made it nearly impossible to think clearly about what is happening, why it matters, and what it means for us.
The geologic record is a speed log. It doesn’t just tell us what conditions existed at different points in Earth’s history. It tells us how quickly those conditions changed -- and what happened to living things when the rate of change crossed certain thresholds.
The pattern is remarkably consistent across billions of years of evidence. Slow change, even change of enormous magnitude, is survivable. The great glacial cycles of the Pleistocene swung global temperatures by four to seven degrees Celsius, repeatedly, over the past 2.5 million years. Global temperature is a long lever with a crucial chemical and biological fulcrum -- in other words, small changes in temperature mean huge variation in everything else. Swings of four to seven degrees caused immense shifts in absolute terms -- enough to bury Northern Europe, Canada, and much of Russia under kilometers of ice, then melt that ice entirely, raising sea levels by well over a hundred meters. Forests migrated, tracking their preferred temperature zones across continents. Animal populations shifted their ranges. Coastlines reshaped gradually enough for ecosystems to reassemble along them. The biological world adapted, because the rate of change was within the range that living systems could match.
The speed at which these transitions occurred is the critical variable. The emergence from the last glaciation -- the transition that brought us from the ice-age world to the warm, stable conditions our entire civilization developed within -- saw warming averaging roughly half a degree Celsius per thousand years. That average is important, even while it is punctuated by sudden jumps.
The warming did not arrive at a steady rate. It came in pulses -- periods of rapid change separated by pauses and even sharp reversals. Around 14,700 years ago, the Bolling-Allerod warming event produced several degrees of temperature increase within centuries, dramatically faster than the millennial average suggests. Then, around 12,900 years ago, the Younger Dryas plunged temperatures back toward near-glacial conditions for over a thousand years before warming resumed and carried the planet into the Holocene -- the stable, warm period in which everything we recognize as civilization was subsequently built.
These oscillations matter because they reveal something about how the climate system behaves under stress. Think of how pressure builds along a fault line. The stress accumulates slowly, over decades or centuries, through the gradual movement of tectonic plates. Nothing visible happens at the surface. The system absorbs the strain. And then, when the accumulated stress exceeds the strength of the rock, the fault slips and the energy is released all at once. The earthquake is not a new event -- it is the sudden expression of pressure that was building long before anyone felt it. And once the fault has slipped, the consequences play out on their own timetable. The buildings have already fallen. The tsunami is already traveling. Knowing that the pressure source has stopped does not undo the damage already committed into the system.
This maps directly onto what we now understand about atmospheric carbon dioxide and the climate’s response to it. Carbon dioxide accumulates in the atmosphere over decades. Its warming effects arrive after the accumulation, because the climate system takes time to respond -- oceans absorb heat slowly, ice sheets respond on the scale of decades to centuries, permafrost thaws gradually and releases additional greenhouse gases as it does. This means that even if all emissions stopped tomorrow, a measurable degree of additional warming is already locked into the system. The carbon is already there. The oceans are still absorbing its heat. The ice is still responding to temperatures that arrived years ago. The effects arrive after the cause, the way an earthquake’s destruction arrives after the fault has slipped. That lag is not a comforting delay. It is a commitment -- a portion of the consequences that is now physically inevitable regardless of any decision we make going forward.
Over the full course of roughly ten to fifteen thousand years, the planet warmed by approximately four to seven degrees from its glacial maximum to Holocene conditions. The pace, despite its pulses and reversals, was slow enough overall that the biological world could keep up. Forests don’t move fast, but they don’t need to when the temperature zones they’re tracking shift at a rate measured in meters per year. Evolutionary pressure exists across these transitions, but it operates on timescales that allow genetic adaptation across generations. Species that couldn’t adapt fast enough went extinct -- the Pleistocene megafauna losses are partly a story of rate-limited adaptation -- but the biosphere as a whole restructured successfully.
The geological record also contains evidence of what happens when the rate doesn’t just increase, but spikes beyond anything the system has experienced in millions of years.
Curious diggers around the world have found the remnants of five events so catastrophic that they reset the trajectory of life on Earth entirely. They are called mass extinctions, and every one of them correlates not with a particular temperature or a particular atmospheric composition, but with a rapid rate of change -- a sudden compression of what would normally unfold over hundreds of thousands or millions of years into a window too short for living systems to adapt.
The Permian-Triassic extinction, 252 million years ago, was the worst. Estimates of the destruction vary, and the variation itself tells a story about the difficulty of counting what is missing from a 252-million-year-old fossil record. Depending on the counting method, the dataset, and how you define “species” in a record composed of the shell fragments and bits of bone that could be turned into stone, current peer-reviewed estimates range from roughly 80% to as high as 96% of marine species eliminated. Roughly 70% of terrestrial vertebrate species disappeared. A 2025 Stanford study published in Science Advances uses “upward of 80%” of marine species; Britannica’s synthesis says “more than 95 percent of marine species”; a 2024 review in ResearchGate uses the 96% figure. By any measure, life on Earth came closer to complete erasure than at any other documented point in its history.
The leading explanation involves massive volcanic eruptions in what is now Siberia -- a geological formation called the Siberian Traps. These eruptions released enormous quantities of carbon dioxide over a geologically short period. A 2021 study published in Nature Communications reconstructed the atmospheric CO2 record across the extinction boundary and found a roughly sixfold increase -- from about 426 parts per million to approximately 2,500 parts per million -- within about 75,000 years. That is the rate that killed nearly everything.
You can work through the mechanism yourself. It does not require a climate science degree, only arithmetic and basic chemistry. Pump that volume of carbon dioxide into the atmosphere at that rate, and the physics produces warming. The warming changes ocean chemistry -- dissolved CO2 makes water more acidic. The acidification kills marine organisms that build calcium carbonate shells and skeletons, because the chemistry of the water they live in is changing faster than their biology can adjust. Oxygen levels in the ocean drop as warmer water holds less dissolved gas and as microbial activity shifts. The cascading effects -- warming, acidification, oxygen depletion -- operate simultaneously and compound each other. The killing mechanism isn’t any single factor. It is the rate at which all of them arrive together.
Volcanism has occurred throughout Earth’s history without triggering mass extinction. What distinguished the Siberian Traps was the rate at which carbon entered the atmosphere relative to the ocean and biosphere’s capacity to process it. The comparison to the present: Pre-industrial atmospheric CO2 was approximately 280 parts per million. We are currently at approximately 425. The Siberian Traps produced a sixfold increase in 75,000 years. We have produced a 50% increase in approximately 200 years. Nearly two-thirds of it happened in the last 50. Almost a third happened in the last 20. The arithmetic speaks for itself.
The end-Cretaceous extinction, 66 million years ago -- the one that ended the age of dinosaurs -- was triggered by a different mechanism but demonstrates the same principle. The Chicxulub asteroid impact ejected enough material into the atmosphere to block sunlight globally, collapsing photosynthesis-dependent food webs within a timescale no terrestrial ecosystem could match. The dinosaurs did not die simply because they were poorly adapted. They died because the rate of environmental change exceeded their adaptive capacity by orders of magnitude. Given geological time, they might well have adapted to a cooler, darker world. They were not given geological time. They were given years.
As in physics, rate is the variable that kills. Not temperature. Not chemistry. Not geography. Speed.
The pattern just documented -- the lethality of rate rather than magnitude -- operates at every scale of biological organization, right down to the molecular level and to the rhythms of daily life. It is not an abstract principle. It is something you have felt.
In 2017, Jeffrey Hall, Michael Rosbash, and Michael Young received the Nobel Prize in Physiology or Medicine for decades of work uncovering the genetic mechanism of the circadian clock. What they found is that in nearly every cell in our bodies, a tiny, self-regulating clock is ticking, encoded in our DNA. The mechanism is a feedback loop of extraordinary elegance. A specific set of genes -- Period and Timeless among them -- produces proteins that accumulate inside the cell’s nucleus throughout the night. Once these proteins reach a critical concentration, they switch off the very genes that created them. Over the course of the day, the proteins degrade, their concentration falls, the inhibition lifts, and the genes switch back on, restarting the cycle.
This rise and fall of protein levels takes roughly twenty-four hours. It is the molecular echo of a single rotation of the Earth. The same basic mechanism operates in fruit flies, in fungi, in cyanobacteria -- organisms so different they share almost nothing else in their biology. What they share is this: They evolved on a world that rotates once every twenty-four hours, and the rhythm of that rotation is embedded in their molecular machinery so deeply that it persists even when the external cues are removed. Humans kept in total darkness, isolated from all time cues, still cycle on an approximately twenty-four-hour rhythm. The clock is not responding to daylight. It is carrying an expectation of consistency that has been part of the architecture of life for hundreds of millions of years.
This clock orchestrates far more than sleep. Hormone release, metabolism, immune response, body temperature regulation, cell repair, gene expression patterns across thousands of genes -- all are synchronized to this twenty-four-hour cycle. It is a system refined across evolutionary time, operating on one non-negotiable assumption: That tomorrow will resemble today.
We know the system exists because we can feel it break. Jet lag is not mere discomfort. It is a measurable, system-wide dysfunction produced when a human body is transported across time zones faster than its molecular clocks can adjust. Your cognition impairs. Your digestion disrupts. Your immune response falters. Your mood destabilizes. Your body is still operating on yesterday’s rhythm while the sun insists on today’s. The system needs days to resynchronize -- and this is from a shift of mere hours, in a rhythm that resets every single day.
The circadian clock is the most molecularly documented case, but the principle it demonstrates -- that biological systems are optimized for predictability and degrade when that predictability is disrupted -- extends through every layer of daily experience. The gut microbiome, calibrated over years to specific dietary inputs, responds to abrupt changes with inflammation, disrupted serotonin production, and measurable shifts in mood and cognition. Cortisol, the hormone that governs the body’s stress response, follows a diurnal pattern that assumes a predictable cycle of activity and rest; chronic disruption of that pattern -- shift work, sustained anxiety, irregular sleep -- produces effects that accumulate over months and years. The first coffee of the morning is not a preference. For most adults, it is the chemical prerequisite for their own baseline cognition. The term “comfort food” encodes the relationship directly: Familiar ingestion as a mechanism for psychological regulation. The comfort is not in the nutrition. It is in the predictability.
We are, from the DNA up, creatures that run on consistency. We function when the inputs are stable; even if they are stable in ways we can objectively recognize as traumatic, animals including humans value “what they are used to”. We degrade -- measurably, physiologically, cognitively -- when they are not. This is not a weakness. It is the operating condition of every biological system that has survived by calibrating to its environment over evolutionary time. The calibration is the adaptation. And the calibration has a speed limit: It can adjust, but only as fast as the processes that built it allow.
If a system calibrated to a twenty-four-hour rhythm cannot handle a six-hour displacement without days of dysfunction, what happens when systems calibrated to millennia-scale transitions encounter change compressed into decades?
The answer is already visible in the biological world. Plants and their pollinators evolved together over millions of years, synchronized to seasonal rhythms that are now shifting faster than either partner can track. The cherry blossom records of Japan -- one of the longest phenological datasets in the world, spanning over a thousand years -- show that blooming is now occurring weeks earlier than it did fifty years ago. Pollinators may emerge on a different schedule, creating timing mismatches that reduce pollination success. The trees flower. The bees arrive late. Both systems fail -- not because either is incapable of handling the new conditions, but because the synchronization between them has been broken by the speed of the change. Migrating birds arrive at breeding grounds to find their food sources already peaked and gone. Coral reefs that took thousands of years to build are bleaching in single seasons because water temperature is shifting faster than coral genetics can accommodate. None of these organisms are dying because they encountered a temperature they cannot survive. They are dying because a rate of change they cannot match has broken the timing relationships their survival depends on.
The same dependency on predictability governs human societies -- and at a scale most people never consider, because it is the background of everything they have ever known.
Every founding civilization grew where specific environmental conditions permitted agriculture at consistent scale. The Nile, the Tigris-Euphrates, the Indus, the Yellow River -- these are not incidental features of the cultures built along them. They are the reason those cultures exist. The annual flood pattern, the seasonal rainfall, the temperature range that permitted specific crops -- these were the preconditions. Everything that followed -- the cities, the trade routes, the legal systems, the religions, the armies -- was built on top of agricultural surplus made possible by climatic consistency.
Modern societies inherit those locations and that dependency. Cairo sits where it sits because of the Nile. London sits where it sits because of the Thames. Shanghai, Baghdad, New Orleans, Mumbai, Dhaka -- every one of these cities exists at a specific geographic point because the environmental conditions at that point, across the centuries during which the city grew, were consistent enough to support continuous settlement. The infrastructure that serves these cities -- ports, power grids, water treatment systems, highway networks, rail corridors -- is immobile. It was designed for the conditions that existed when it was built, and it assumes those conditions will persist. The assumption is embedded in every foundation, every zoning map, every thirty-year mortgage.
Each generation treats the conditions it inherits as the baseline -- not as one frame in a sequence that has included radically different configurations. The Holocene’s relative climatic stability is an anomaly in the geologic record, a brief calm interval during which a particular species of primate happened to invent agriculture and build everything that followed. But no one alive has experienced anything else. No human civilization has experienced anything else. Our planning horizons reflect this: 30 to 50 years for infrastructure, two to four years for political systems, less than a year for most individual decisions. None of these horizons contain the possibility that fundamental geographic and climatic conditions could change faster than the planning cycle can respond to them. The safeguard against this blindness -- institutional memory, long-range planning, intergenerational knowledge transfer -- exists, but it is the exception, not the norm. Most societies plan for the next harvest. The next election. The next quarter.
Consider what you do for a living. Not whether you enjoy it or whether it pays well, but whether it is the kind of work a society under sustained pressure would continue to need. Food production. Water management. Energy infrastructure. Medical care. Physical construction. Security. These are the activities that societies prioritize when surplus contracts -- when the margin between what is produced and what is required narrows. The service economy, the knowledge economy, the creative economy -- these are expressions of surplus. They exist because the underlying systems produce enough that not everyone is required to maintain them. The question of what happens to those economies when the underlying systems strain is not speculative. We have a recent, global, vivid memory of what even a temporary disruption to supply chains, institutional capacity, and daily routine felt like -- and how quickly the distance between normality and crisis turned out to be shorter than almost anyone had assumed.
These are the characters in the story this series documents. The body, calibrated to consistency at the molecular level. The society, anchored to geography it cannot move and planning horizons that cannot see what is coming. The biosphere -- the ecological web that both of these depend on for food, water, pollination, atmospheric regulation, and a thousand other services that function only because the species providing them are synchronized to each other and to the conditions they evolved in.
The biosphere’s current condition is documented in the same units this episode has been using: Rate.
Current species extinction rates are estimated at 100 to 1,000 times the background rate documented in the fossil record. The range depends on the assumed background rate -- a 2015 study by Ceballos and colleagues, published in Science Advances, used conservative assumptions and found vertebrate species loss over the past century running up to 100 times faster than the background rate. A 2014 study by De Vos and colleagues revised the background rate itself downward by an order of magnitude, pushing the ratio toward 1,000 times. What would have taken between 800 and 10,000 years under natural conditions has been compressed into a single century.
The mechanisms are different from the Siberian Traps and different from Chicxulub. Habitat destruction, deforestation, freshwater diversion, ocean acidification, agricultural monoculture, the introduction of invasive species across biogeographic barriers that evolution maintained for millions of years. No single volcanic province. No asteroid. Just the cumulative footprint of eight billion people and the infrastructure that supports them, arriving faster than the biosphere’s adaptive mechanisms can absorb.
Five times in Earth’s history, a rapid rate of environmental change has crossed the threshold that the living world could not match. The geologic record documents those five events in strata that any graduate student with the right training can read. The current rate data sit beside the five previous episodes in the same units, at the same scale, measured by the same methods. The comparison requires no editorial assistance. The numbers are in the same column.
The speed limit is real. It is measurable. It operates at every scale of organization -- molecular, ecological, civilizational.
At the molecular level, the circadian clock demonstrates that life is calibrated to specific rates of change, and that even small disruptions in rate produce systemic dysfunction. At the ecosystem level, the documented mismatch between pollinators and flowering plants, between migrating species and their food sources, between coral and ocean temperature, demonstrates that the current rate of environmental change is outpacing the adaptive capacity of systems that have functioned for millions of years. At the civilizational level, eight billion people live in societies anchored to specific locations, dependent on climatic consistency those locations have provided for the duration of recorded history, planning on horizons that do not include the possibility of that consistency ending.
Five mass extinctions are in the record. The current biodiversity data occupy the same analytical space. Stability is a baseline requirement for everything we have built, and we have benefited from it for so long that we mistake it for a permanent feature of the world rather than a temporary condition of it.
What rate of change are we producing now? What infrastructure have we built that generates that velocity? And is it even physically possible to operate on the scale we have built without affecting the vanishingly thin atmospheric layer that constitutes our climate?
This has been an episode of Polite Disputes. Thanks for listening.
