When I talk about climate risks, I usually think about temperatures rising, ice melting, extreme weather, droughts, floods, fires, and all the stress this puts on ecosystems, economies, and societies. In my mind, carbon dioxide (CO₂) has always been the gas that traps heat in the atmosphere and destabilises our climate systems. That’s the story we have repeated again and again: CO₂ warms the planet.
But recently I came across a scientific review written by Professor Ugo Bardi and colleagues (https://pubs.rsc.org/en/content/articlelanding/2025/va/d5va00017c) that opened a perspective I had never seriously considered. It suggests something quite different: Several studies show that CO₂ itself has direct effects on human health and on the stability of natural systems, beyond the warming it causes. A few months ago, I had the chance to sit down with Ugo for a coffee in Florence. We talked about his research, about how little attention this area has received, and about possible solutions to reduce atmospheric CO₂ concentrations through both nature-based and technological approaches. I left that conversation inspired.
To put things in context: before the industrial era, atmospheric CO₂ was around 280 ppm. For hundreds of thousands of years it rarely exceeded about 300 ppm. Today we are above 420 ppm. Humanity has never lived for generations in air like this. Somewhere along this path we may cross thresholds that affect our bodies and minds, but unlike temperature, we don’t have agreed limits for CO₂. There is no widely accepted “safe” concentration for our health or cognition. We simply don’t know.
As CO₂ concentrations rise in the atmosphere, some early studies suggest there could be small but noticeable effects on how alert we feel and how clearly we think. It’s subtle and often goes unnoticed. We usually blame tiredness or low focus on stress or our routines, but the changing chemistry of the air around us might also play a role. We don’t fully understand these impacts yet, and that’s exactly why more research is needed.
This isn’t only about humans. CO₂ changes the chemistry of oceans by making them more acidic, harming corals, shellfish, and marine food chains. It can change how plants grow and alter the nutritional value of crops. These effects happen because of chemistry, not temperature. They are part of the same story, but we rarely connect them when we talk about climate change.
What surprised me most is how little attention this topic receives. Climate science has focused on modelling heat, rainfall, and extreme events. Health researchers mostly look at smoke, ozone, and particulates. Almost no one studies the slow and subtle effects of elevated CO₂ on human cognition, productivity, learning, or psychological wellbeing. We don’t know whether children are more sensitive. We don’t know how lifelong exposure influences ageing or memory. We don’t know how the biology of large-brain mammals reacts to slow changes in atmospheric composition. These open questions don’t mean danger, they mean uncertainty.
In a recent essay titled Three Tough Truths about Climate, Bill Gates wrote that climate action should not only be about reducing emissions or limiting temperature increases, but about improving people’s lives. That simple idea changes how we think about risk. If CO₂ levels are influencing cognition, learning, and wellbeing, then reducing CO₂ becomes not only a climate imperative but a health and human-development one.
It also reframes motivation. When we reduce emissions and remove CO₂ from the atmosphere, we’re not just protecting polar bears or distant generations. We might be improving the quality of the air we breathe, how we sleep, how we learn, and how productive we feel. It adds a human layer on top of the planetary one.
Today we already have a wide portfolio of approaches to reduce atmospheric CO₂ concentrations. Some are nature-based , restoring forests, soils, coastal ecosystems. An interesting possibility is to use algae to reduce CO₂ concentrations indoor. Algae are more efficient than land plants in terms of photosynthetic yield, and they can be cultivated wherever it is not possible to use trees or other plants to purify the air, as in indoor environments. Others methods are technological: direct air capture and sequestration, mineralisation, bio-oil sequestration, enhanced weathering. None are perfect, many are expensive, but they show that innovation continues to move. The International Energy Agency has already changed its forecasts significantly over the past decade because clean technologies (mainly referring to Renewable Energy) are scaling faster than expected. As Bill Gates notes, progress often surprises us. We are not powerless, and we are advancing. Emissions reduction must always come first, but accelerating solutions strengthens our ability to protect both planetary and human health.
Climate has always felt like something outside the weather, the environment, the physical world. But this perspective brings it inside. Into our lungs, our homes, our bodies, our minds. It reminds us that the boundary between “planetary health” and “human health” is thinner than we think.
We need to measure, observe, and learn. If these effects turn out to be negligible, that’s great news. If not, we’ll want to know early enough to act. Either way, this is a question worth asking.
Because when we change the chemistry of the atmosphere, we are not only changing the climate of the planet. We are also changing the chemistry of the world we breathe in, every single second of our lives. And that deserves our attention.
Loved the human, clear and realistic approach on the matter.