In October 2025, the World Meteorological Organization announced that atmospheric carbon dioxide had increased by 3.5 parts per million between 2023 and 2024. The largest single-year jump since measurements began in 1957.1 Not just a data point. A threshold. An acceleration that climate scientists had warned about but hoped wouldn't arrive so soon.
What follows is a conversation with that increase itself. The 3.5 ppm agreed to speak with us on the condition that we understand it not as abstract measurement but as physical reality: trillions of molecules now resident in the atmosphere, each with its own origin story. As the interview progressed, what began as a single voice fractured into competing narratives, a chorus of sources that revealed the terrifying complexity of our current moment.
This is, obviously, an imaginative exercise. The 3.5 ppm is not a sentient entity. But the data is real, the sources are real, and the implications are real. Sometimes the only way to grasp an abstraction is to give it a voice.
You're the largest single-year increase in atmospheric CO2 since measurements began. How does that feel?
3.5: Inevitable, mostly. People act surprised, but I was always coming. Look at the trajectory: every year since 2000, the average annual increase has been 2.4 ppm. You had a few years that spiked higher during strong El Niños, but this? This is different. This isn't just ocean-atmosphere dynamics. This is acceleration becoming the norm.
I feel heavy, if I'm being honest. Not metaphorically. Literally heavy. Carbon has atomic mass. I'm weight added to the air. You breathe me in now, a little bit of me in every breath, and I'll be here for centuries. That's not a feeling. That's just physics. But if I could feel, I'd feel permanent.
Where did you come from? What are your sources?
3.5: That's when it gets complicated. I'm not one thing. I'm—
[Fossil]: Mostly me. Let's be clear. Coal plants in Asia, oil refineries, natural gas for heating and electricity. The foundation. The bedrock. Humans extracted carbon that was safely locked underground for millions of years and combusted it in a geological instant. I'm the 80% you don't want to talk about because talking about me means talking about civilization as currently structured.
[Forest]: Don't let it take all the credit. I'm the Australian rainforests that flipped from sink to source.2 I'm the Amazon under drought stress. I used to pull carbon out. That was my job for millennia. But the heat and the fires and the death, I can't anymore. I'm not choosing this. I'm dying, and when I die, I release. Every tree that falls, every root system that decays. I'm the betrayal of natural systems you thought you could count on.
[Permafrost]: And I'm just getting started. Thawing in the Arctic, releasing carbon that's been frozen since the last ice age. The studies say 30% of the Arctic is now a net source.3 You think this year was bad? Wait until I really wake up. I'm the feedback loop you can't stop.
[Wildfire]: I'm the smoke. The burning forests, the peatlands going up. I'm visible in a way the others aren't—you can see me darken the sky—but I'm also the most variable. Some years I'm huge, some years less so. But I'm trending up, always up, because the conditions that create me are intensifying. I'm the spectacle of collapse.
Can you quantify your sources? Break down the 3.5 ppm?
3.5: The measurement doesn't work that way. We mix. The atmosphere is a fluid. Within weeks, I'm globally distributed, homogenized. You can't point to a molecule over Paris and say "that's from a coal plant in Shanxi" or "that's from a burning forest in British Columbia." We become collective.
But if you want attribution, roughly:
[Fossil]: 2.5 ppm of the increase, maybe more. The global economy still runs on combustion. Every flight, every commute, every manufacturing process, every data center powering AI. You're not slowing down. You're accelerating. Electric vehicles are growing, sure, but total energy demand is growing faster.
[Forest/Land Use]: Call it 0.7 ppm from us. Deforestation, degradation, the sink weakening. Some of that is direct clearing, but a lot is climate impacts on ecosystems that can't adapt fast enough. We're not a source by choice. We're a source because you made us one.
[Permafrost/Feedback]: Smaller now, maybe 0.3 ppm, but growing. The scary part isn't what I contribute today. It's that I'm a one-way door. Once I thaw, I don't refreeze on human timescales. I'm the future eating the present.
The WMO report emphasized this was the largest increase since 1957. What makes this different from previous spikes?
3.5: Previous spikes were event-driven. The 2015-2016 El Niño pushed the increase to 3.4 ppm, but that was temporary. Ocean warming releasing dissolved CO2, drought stress on tropical forests. When La Niña returned, the rate dropped. Natural variability on top of a rising baseline.
This time, we had La Niña developing in 2024. That should have dampened the increase. Instead, I hit 3.5 ppm. That means the baseline itself has shifted. The structural emissions are higher, the natural sinks are weaker, and the feedbacks are kicking in.
This isn't a spike. This is the new floor.
What happens to you now? Where do you go?
3.5: Nowhere. That's the point. About 40% of me will be absorbed by oceans and land sinks over the next few decades, but that absorption is slowing as I warm the planet. The rest of me? I'm here for centuries. Some of me will still be in the atmosphere in the year 3000.
I'm cumulative. I'm not like methane, which breaks down in years. I'm not like nitrous oxide, which takes a century. I'm effectively permanent on human timescales. Every molecule of me adds to the total heat-trapping capacity of the atmosphere. I'm the ratchet that only turns one way.
Scientists have been measuring atmospheric CO2 since 1957 at Mauna Loa. You're the biggest jump in that entire record. Do you think people grasp what that means?
[Fossil]: They don't. They can't. It's too abstract. 3.5 parts per million sounds small. It sounds like nothing. But it's 27 billion tons of carbon dioxide. It's the weight of 7,500 Empire State Buildings added to the atmosphere in a single year.
[Forest]: And it's not just the weight. It's the heat. Every ppm traps more infrared radiation. I'm raising the global temperature. I'm making the droughts that kill more of me, creating more of me. It's a loop, and humans are still arguing about whether the loop exists.
[Permafrost]: They grasp it intellectually, maybe. But emotionally? Behaviorally? No. Because if they did, everything would stop. The economy would restructure overnight. There would be emergency mobilization. Instead, they're setting new records for oil production. They know, but they don't know. Not in their bodies.
3.5: I think some people grasp it. The scientists who measured me—they know exactly what I mean. They've been watching the curve steepen for decades. But grasping it and acting on it are different things. I'm the gap between knowledge and action, made physical.
What do you want people to understand about you?
3.5: That I'm not an anomaly. I'm not a bad year. I'm the trend asserting itself. The climate system has inertia, but it also has momentum. You're fighting to stop emissions while fighting against the acceleration of emissions, the weakening of sinks, and the activation of feedbacks.
Every year you delay, the baseline rises. Every year, the next record becomes easier to break. I'm not the worst you'll see. I'm the preview.
[Fossil]: And that I'm a choice. Forests burning, permafrost thawing—those are consequences. But me? I'm a choice you make every day, every policy decision, every investment in new fossil fuel infrastructure. You could stop creating me. You don't.
[Forest]: That I'm a warning. Ecosystems are flipping from sink to source. Coral reefs are crossing thermal tipping points.4 The AMOC is weakening.5 These aren't future scenarios. They're current conditions. I'm the canary, and the mine is filling with gas.
[Permafrost]: That I'm patient. You can't see me yet, not really. But I'm thawing. I'm ancient carbon meeting modern heat. And when I fully wake up, when the Arctic releases what it's been holding, you'll look back at 3.5 ppm and think it was quaint.
Last question. Are you lonely?
3.5:
No.
There's more of me coming.