The Other CO₂ Threat

Are we being poisoned in addition to being boiled alive?

Reposted from Futuribles — a post by Eduardo Martinez de la Fe — AI created image.

For decades, one question has lingered in the background of evolutionary thought: why did no dinosaur, in 170 million years, ever develop intelligence comparable to our own?

They had time. They faced evolutionary pressures. Some species, such as Troodon, even had relatively large brains. And yet the cognitive barrier remained in place.

A preprint by Ugo Bardi (a professor at the University of Florence and a member of the Club of Rome) offers an arresting answer: atmospheric CO₂ may have set the limit. During the Mesozoic, concentrations were between five and ten times higher than they are today. Dinosaurs lived in an atmosphere that simply left too little metabolic room for brains as energy-hungry as ours.

The metabolic brake

We breathe in oxygen and breathe out CO₂. But when carbon dioxide builds up in the surrounding environment, the body becomes less efficient at getting rid of that waste product, and the reaction that powers our cells begins to slow. In plain terms, more CO₂ means less usable energy.

A 2024 paper by neuroscientist Richard Buxton of the University of California San Diego showed that the oxygen-to-CO₂ balance in brain tissue is crucial. As CO₂ rises, the energy available to sustain neural activity falls.

Bardi takes that physiological rule and applies it on a geological timescale. Over millions of years, as atmospheric CO₂ fell (from roughly 1,600 ppm to the pre-industrial 280 ppm) evolution gained access to more energetically expensive possibilities. In his reading, the long decline in carbon dioxide gradually opened the way to more complex brains. Intelligence, in that sense, was not simply selected for; it was made metabolically possible.

Why this matters now

If CO₂ once constrained cognitive evolution, raising it again should give us pause. In May 2026, outdoor concentrations at Mauna Loa passed 432 ppm, the highest level in the modern record.

The more immediate issue, however, lies indoors. Experimental evidence has already shown measurable cognitive effects at concentrations commonly found in classrooms, offices and poorly ventilated buildings.

A study from the Lawrence Berkeley National Laboratory found that at 1,000 ppm, decision-making performance declined significantly on six out of nine measures. Research from the University of Colorado projected that, if current trends continue, indoor concentrations could reach 1,400 ppm by the end of the century, a level at which decision-making may fall by 25 per cent and strategic thinking by as much as 50 per cent. Researchers at UCL have likewise reported cognitive decline in a substantial share of the studies reviewed once CO₂ rose above those levels.

Bardi’s argument links these two scales: the deep history of life and the air in the rooms where we now spend most of our time. Biologically speaking, we may be nudging the atmosphere back towards conditions less favourable to complex cognition.

A warning worth taking seriously

The research is still under review, and extending present-day physiology across the whole sweep of evolutionary history is obviously a bold move. Even so, the statistical pattern is striking, and the underlying physiological mechanism is grounded in recent peer-reviewed work.

Futures studies teach us to pay attention to weak signals. This looks like one of them.

There is no need to wait for every palaeontological detail to be settled before drawing a practical conclusion. The medical and environmental evidence already gives us ample reason to take air quality far more seriously, not only at planetary scale, but in schools, offices and homes. It is a disturbing thought that the very intelligence allowing us to grasp the consequences of emissions may be among the first capacities placed under pressure by them.

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