The Carbon Dioxide in the atmosphere, by volume, is _______?

Carbon dioxide (CO₂) is a naturally occurring gas that is present in Earth’s atmosphere in very small quantities compared to other gases like nitrogen and oxygen. By volume, carbon dioxide makes up about 0.039% (or 390 parts per million, ppm) of the atmosphere. Although this percentage seems extremely small, carbon dioxide plays a crucial role in regulating the planet’s temperature and supporting life.

CO₂ is a greenhouse gas, meaning it traps heat energy in the atmosphere and helps maintain Earth's temperature. Without greenhouse gases like CO₂, our planet would be too cold to sustain life as we know it. However, an increase in carbon dioxide levels beyond natural limits contributes to global warming and climate change.

The primary natural sources of atmospheric carbon dioxide include respiration by living organisms, volcanic eruptions, decomposition of organic matter, and ocean release. Human activities such as burning fossil fuels (coal, oil, natural gas), deforestation, and industrial emissions have significantly increased CO₂ levels over the last century.

The incorrect options are:

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  3.9%: This is 100 times higher than actual levels and does not match atmospheric measurements.

  
  


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  13% and 30%: These values are far above the real concentration. Oxygen makes up around 21% of the atmosphere, and nitrogen about 78%, leaving only a small fraction for CO₂ and other trace gases.

  
  

Even at just 0.039%, carbon dioxide is essential for photosynthesis, the process by which plants make food and release oxygen. It also plays a major role in the Earth’s carbon cycle and maintaining climate balance.

Thus, the correct answer is 0.039%, highlighting the significance of even trace gases in maintaining life and environmental stability on Earth.