Carbon dioxide (CO2) is a big deal. This clear, odorless gas is everywhere; composing around 0.04%1 of Earth’s atmosphere – that’s a lot.  
And while it is naturally occurring, there’s some controversy about how CO2 affects humans, and how humanity affects CO2. Let’s get to the bottom of it.  

  • What is CO2
  • The carbon cycle
  • The greenhouse effect
  • Where does CO2 come from?
  • How does CO2 affect humans? 

What is CO2

First off, CO2 is not a “bad,” human-made phenomenon. In fact, all life on Earth is based on carbon. This is because this element easily forms bonds with other molecules, including other carbon molecules. Because of this capacity, long, complex molecular chains are possible: proteins, DNA, sugars, etc.  
The combination of one carbon and two oxygen molecules (CO2), is essential for the planet’s carbon cycle, the greenhouse effect, and life as we understand it.  
What is the carbon cycle?  

The carbon cycle is the natural process of how carbon moves throughout the air, ground, plants, animals, and fossil fuels of Earth. It is a fundamental process. Humans and animals breathe in oxygen and release it as CO2. On the other hand, plants absorb CO2 for use in photosynthesis, releasing pure oxygen as their byproduct.  
In addition to living creatures, carbon also progresses throughout the oceans, atmosphere, and land formations of rock, soil, etc. When these structures break down, their carbon is released back into the atmosphere, where it can be (re)absorbed by oceans, plants, forests, etc., returning to the cycle.  

What is the greenhouse effect? 

Here, we will start with how greenhouses work. A greenhouse is a special structure designed to help plants grow by staying warmer (and more humid) than outside. Light from the sun streams through the windows or siding of the greenhouse, warming the surfaces, objects, and plants within.  
Sunlight contains the entire electromagnetic spectrum: radio waves, microwaves, infrared radiation, visible light, ultraviolet (UV) radiation, X-rays, and gamma rays. For brevity, we will narrow our focus to just visible light and infrared radiation.  
Both visible light and infrared radiation can pass through the glass or plastic of a greenhouse, as these waves have a small wavelength (size). Once through, however, they bounce off the materials and plants within, increasing the size of their wavelength. This traps their energy and heat inside.  
The greenhouse effect is a natural phenomenon describing how Earth’s atmosphere responds to light from the sun (solar radiation). While Earth’s atmosphere absorbs, reflects, or scatters much of this energy, some of it is trapped within the atmosphere – warming the plant similar to how greenhouses do. Gases responsible for the greenhouse effect include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), water vapor, etc. With more greenhouse gases, the atmosphere heats up.  


Where does CO2 come from? 

The majority of carbon dioxide naturally occurs as part of the planet’s carbon cycle detailed above. From there, fires and volcanic activity also release large amounts of carbon into the atmosphere.  
Human activity also plays a role in “producing” this gas. As people mine, harvest, and burn fossil fuels for energy, the levels rise as these previously buried and contained sources of carbon are released into the atmosphere. When humans reduce plant life via deforestation, this also increases carbon levels, as flora absorb significant amounts of CO2.  


How does CO2 affect humans? 

Exposure to high levels of CO2 is problematic.2 While “normal” concentrations in the outdoors hover around 420 parts per million (ppm), increased levels can result in problems. Above 1000 ppm, human cognitive abilities are reported to drop by 15%. In other words, we need oxygen to think. At 1500+ ppm, cognitive function drops by 50%. Furthermore, as CO2 levels increase, people have access to less oxygen. This can result in feelings of drowsiness and fatigue. It is also possible to experience fatigue, headaches, nausea, and respiratory problems.  
It is also worth noting that concentrations of CO2 are a direct indication of poor indoor air quality. It means that an area is poorly ventilated, and that there is a higher likelihood of inhabitants being exposed to bacteria, mold, dust, pet dander, volatile organic compounds (VOCs), and other unwanted materials.  
One of the easiest ways to be aware of CO2 levels is by using an air quality monitor. The current market leader is the Aranet4 – a portable, wireless device that keeps track of CO2, temperature, humidity, and atmospheric pressure. Additionally, all the data gathered by these monitors is stored on a mobile application for easy tracking. Keeping an eye on these health-centric parameters is a fantastic way to know when to ventilate or leave an unsafe area. 


How are governments managing CO2

While the topic of carbon emissions has become increasingly worrisome for many people, significant steps are being taken to reduce production. World governments are increasingly making regulations on reducing CO2 emissions. Some of the most popular avenues for these efforts are: 

  • Reducing Greenhouse Gas Emissions: This mostly infers to transitioning away from burning fossil fuels and gravitating toward renewable energy sources: solar, wind, geothermal, nuclear, hydroelectric, etc. This also includes improving how efficiently energy is used in production, travel, heating, cooling, and other human activities.  
  • Carbon Capture and Storage (CCS): Instead of releasing CO2 into the atmosphere, these technologies aim to capture previously released carbon, storing it instead. 
  • Afforestation and Reforestation: This is the act of planting new trees and replanting deforested areas. Trees absorb CO2 and store it for use in photosynthesis. 
  • Carbon Pricing: This is a governmental policy that puts actual costs on companies through taxes or other measures. As the bottom line is a fundamental concern for any business, this is a particularly effective method.
  • International Cooperation: Different countries have different levels of emission and pollution. However, efforts like the Paris Agreement are geared toward keeping every country committed to reducing their carbon footprint and keeping overall levels lower.  

How are people managing CO2?

When it comes to creation., people can reduce their carbon footprint by using less energy, having efficient appliances, driving less, and engaging in other sustainable and renewable efforts. 

However, CO2 concentrations indoors will increase as people breathe the air. This is best prevented with effective indoor ventilation. This can include, but is not limited to, opening windows, managing heating, ventilation, and air conditioning (HVAC) systems, using vents, and allowing air to circulate, rather than being trapped in increasingly stale environments.  

Additionally, activities like cooking can cause spikes in CO2, especially when using gas burners and other open flames. For this reason, it’s a good idea to use range hoods and fans while preparing food.

Ultimately, carbon dioxide is a natural part of life on Earth. It is harmless in small quantities but becomes a problem in large concentrations. Fortunately, monitoring CO2 levels and staying safe is easy with the right equipment.  



  1. The Atmosphere: Getting a Handle on Carbon Dioxide. 
  2. Impacts of Indoor Air Quality on Cognitive Function. 

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