Final answer:
Carbon dioxide, one of the most important greenhouse gases, makes up 0.04% of Earth's atmosphere.
Step-by-step explanation:
Carbon dioxide (CO₂) makes up a small but very important portion of Earth's atmosphere. While water vapor is the primary greenhouse gas responsible for about 80 per cent of the natural greenhouse effect, CO₂ contributes significantly as well, accounting for approximately 0.04% of the total Earth's atmosphere. This proportion, though it seems small, has a large impact on the climate. The current atmospheric CO₂ concentration is about 400 part per million (ppm), which has increased from pre-industrial levels due to human activities such as burning fossil fuels and deforestation, thereby contributing to the enhanced greenhouse effect and global warming.
The importance of CO₂ lies not just in its ability to trap heat but also in its abundance and persistence in the atmosphere. The concentration of CO₂ has rapidly increased since the Industrial Revolution, altering the natural carbon cycle. As a greenhouse gas, CO₂ is responsible for around 8°C of the average global temperature increase that makes our planet habitable, a crucial component in preventing Earth from becoming an ice planet.