Different Effects of CO₂ on Humans and Plants

Carbon dioxide (CO₂) is a naturally occurring gas essential for life on Earth. However, its concentration in the atmosphere has been increasing due to human activities, leading to various impacts on both humans and plants. Below is a detailed comparison of its effects:

1. Effects of CO₂ on Humans

A. Physiological Effects

​Respiration & Blood pH:

  • High CO₂ levels (>1,000 ppm) can cause ​hypercapnia (excess CO₂ in blood), leading to headaches, dizziness, and shortness of breath.

  • CO₂ dissolves in blood, forming carbonic acid (H₂CO₃), lowering blood pH (respiratory acidosis).

​Cognitive Function:

  • Elevated CO₂ (≥1,000 ppm) reduces cognitive performance, affecting memory, decision-making, and focus.

  • At 2,500 ppm, significant impairment occurs (studies in classrooms and offices).

​Sleep Quality:

  • High indoor CO₂ levels (e.g., poorly ventilated bedrooms) may disrupt sleep patterns.


B. Long-Term Health Risks

  • ​Cardiovascular & Respiratory Issues: Chronic exposure to high CO₂ may worsen heart and lung conditions

  • Indoor Air Quality (IAQ): Buildings with poor ventilation accumulate CO₂, leading to "sick building syndrome" (fatigue, nausea).


C. Indirect Effects (Climate Change)

  • Global Warming: CO₂ is a greenhouse gas, contributing to rising temperatures, extreme weather, and heat-related illnesses.

  • Air Pollution: Higher CO₂ levels correlate with increased ground-level ozone and particulate matter, worsening asthma and lung diseases.

2. Effects of CO₂ on Plants

A. Positive Effects (CO₂ Fertilization Effect)


Enhanced Photosynthesis:

  • Plants use CO₂ for photosynthesis (6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂).

  • Elevated CO₂ (500–1,000 ppm) can boost growth in C3 plants (wheat, rice, soybeans) by up to 30%.

​Water Use Efficiency: Higher CO₂ reduces stomatal opening, decreasing water loss (beneficial in droughts).


​Crop Yields: Some crops (e.g., wheat, barley) show increased yields under elevated CO₂.


B. Negative Effects


Nutrient Dilution: Faster growth can reduce nutrient density (e.g., lower protein, zinc, iron in crops).


Weed & Pest Proliferation: Invasive weeds (e.g., kudzu) benefit more than crops, increasing competition.


Ocean Acidification: Excess CO₂ dissolves in oceans, lowering pH and harming marine plants (e.g., coral reefs, phytoplankton).



C. Climate Change Impacts


​Temperature Stress: While CO₂ boosts growth, extreme heat and droughts (linked to climate change) can negate benefits.


Ecosystem Shifts: Some plants may thrive, while others decline, altering biodiversity.

3. Conclusion

  • Humans are negatively affected by high CO₂ (indoor air quality, climate change).

  • ​Plants benefit from moderate CO₂ increases but face trade-offs (nutrient loss, climate stress).

  • ​Balancing CO₂ levels is crucial—reducing emissions while managing agricultural and ecological impacts.