CO2 Make Dumb

Low atmospheric CO2: a prerequisite to human brain evolution

Rising atmospheric carbon dioxide heats the planet, threatening crops and human health. It also threatens human intelligence. The natural trapping of carbon underground millions of years ago arguably enabled human evolution in the first place. The irony is this carbon sequestration created the fossil fuels we burn today, threatening our existence.

Human intelligence depends on the chemical makeup of the atmosphere. Burning fossil fuels returns the atmosphere to its state before the human brain evolved. Even if humans manage to survive heat, droughts, and famines, a higher concentration of CO2 in the air will devolve humanity back to its primitive level of intelligence, effectively erasing modern humans from the planet.

Photo by BUDDHI Kumar SHRESTHA on Unsplash

Greenhouse Earth

During the Devonian Period, between 419 and 359 million years ago, Earth existed in a high-carbon state. Carbon dioxide concentrations reached 2,000 parts per million, while oxygen levels remained at 15% to 20%. This chemical environment limited the energy available for animals to develop complex brains (why? explained below).

During the Carboniferous and Permian periods, massive amounts of carbon became buried underground to form Earth’s oil and coal deposits. Scientists previously attributed this to a delay in fungi developing the ability to break down wood. Newer research shows that dead plants accumulated in deep, oxygen-poor swamps that prevented decay. (How this happened is irrelevant to my point.)

The burial of undecayed plant matter created a natural carbon sink and permanently shifted the atmosphere by removing carbon from Earth’s surface, allowing oxygen to accumulate. Carbon dioxide dropped to between 180 and 400 parts per million, while oxygen levels rose. This low-carbon, higher-oxygen atmosphere created the baseline energy environment that allowed complex land animals and large-brained humans to evolve.

The Connection between Atmospheric CO2 and the Human Brain

Over three million years, the human brain expanded more than three times in size. It grew to a modern average volume of 1,200 to 1,500 cubic centimeters. The adult human brain makes up 2% of total body weight, but it consumes 20% to 25% of the body’s resting energy. In infants, the brain uses 50% of resting energy.

The human brain contains 86 billion neurons. These cells need a constant supply of chemical energy called ATP (remember learning this in high school science?) to function. Neurons use ATP to power tiny protein pumps that reset electrical charges across cell membranes.

To make ATP, brain cells require glucose and oxygen from inhaled air. High oxygen levels in the surrounding air force oxygen into the lungs and blood. Blood vessels carry this oxygen to the brain, where cells use it to break down glucose and generate ATP. At the same time, burning glucose produces carbon dioxide and acid as waste. The body must remove this waste to keep the brain working correctly. Air with low carbon dioxide levels allows the lungs to release carbon dioxide from the blood into the environment.

If air has too little oxygen or too much carbon dioxide, this exchange fails. Carbon dioxide builds up in the blood and brain, turning the surrounding fluid acidic. This acidity slows down enzyme activity, reduces ATP production, and stops the protein pumps from resetting neuronal electrical charges.

A higher concentration of atmospheric CO2 impairs human thought and cognitive performance. As electrical signaling slows down, the brain loses its ability to process complex information quickly.

Late-evolving parts of the brain are the most energy-intensive and therefore the first to be affected. These parts handle impulse control, abstract thought, long-term strategic planning, and complex decision-making, and are affected long before physiological impairment is noticeable (perhaps we’re already starting to see the effects?).

Breathing air from the Devonian Period, with 2,000 to 4,000 parts per million of carbon dioxide and 15% oxygen, would reduce blood oxygen and raise blood acidity. Carbon dioxide cannot pass from the blood into the lungs. Instead, it accumulates in the blood, enters brain fluid, and turns into acid (note: not “Alien” level acidity...just enough to impair delicate biochemical function).

In response, the brainstem triggers rapid breathing, paradoxically introducing more carbon dioxide into the lungs, worsening blood acidity. High carbon dioxide expands brain blood vessels, raising pressure inside the skull and causing oxygen starvation, swelling, confusion, and seizures.

Of course, it’s unlikely humans experience CO2 concentration of 2,000 to 4,000 parts per million anytime soon. But the effects lie on a spectrum, and at current trajectory it’s not unreasonable to assume surviving future humans (perhaps within decades) could experience atmospheric CO2 concentration of 1,000+ parts per million. Industrial activity has already doubled atmospheric CO2 concentrations.

At carbon dioxide levels between 1,000 and 1,500 parts per million, decision-making performance drops by roughly 25%, and complex strategic thinking drops by 50%. The precision of these estimates are debatable, as measurement is somewhat subjective, but the relationship between higher CO2 concentrations and lower executive functioning is clear.

If pockets of humanity survive the coming heat, crop failures, and drought their brains will still be under attack by higher CO2 concentrations. This will force an evolutionary (or devolutionary) response because large human brains require high energy production and long childhood growth periods. In a high-carbon atmosphere, maintaining a large brain becomes impossible, and natural selection would favor smaller brains, simpler neural wiring, and shorter growth periods to reduce daily energy demands. We would become a less intelligent species.

Human species comes full circle.

The very thing that allowed human brains to grow more intelligent, enabling the development of complex industrial society, is what will drive the species back to pre-human state.

The burial of organic carbon millions of years ago created the low-carbon, high-oxygen atmosphere required for human brain expansion. Releasing that buried carbon reverses those atmospheric conditions.

If there were a master creator in charge, she’s certainly wondering why we’re releasing the chemical they hid that allowed us to thrive. Ancient carbon sequestration was a “gift” to humans that allowed us to exist in the first place.

I’m not a religious person (at least not in the traditional sense), but millions of years of stored energy in the form of fossil fuels was humanity’s great temptation. Leave it in the ground and survive. Use it and have a short orgy of abundance, then self-destruct.

We failed.

Thank you for reading.

My name is Sarah and I run Collapse2050 by myself. It is a passion project to explore humanity’s frightening future - a topic traditional media ignores.

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Sarah