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How does carbon dioxide act as a greenhouse gas?

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A labeled diagram of the periodic table entry for carbon, showing its atomic number 6, symbol C, electron configuration, atomic weight range, solid physical state, hexagonal crystal structure, and weakly acidic oxide properties. Color coding and icons indicate it is a nonmetal, solid at room temperature, with hexagonal structure and weak acidity. — carbon Carbon and its properties.

Carbon dioxide (CO₂) acts as a greenhouse gas by absorbing and re-emitting infrared radiation (longwave radiation) emitted from Earth’s surface.123

The process functions as follows:
* Absorption: While Earth’s surface radiates energy back toward space in the form of infrared radiation, CO₂ molecules absorb a portion of this outgoing energy.13
* Re-emission: Greenhouse gases emit the radiation they absorb equally in all directions, including back downward toward the surface and the lower atmosphere.13
* Warming Effect: This downward re-emission increases the total amount of radiation directed toward the lower atmosphere, causing it to remain warmer than it would be in the absence of these gases.13

Because the lower atmosphere is warmer than the layers above it, this mechanism effectively traps heat, contributing to the greenhouse effect. While this is a natural process essential for maintaining a habitable planetary temperature, human activities—primarily the burning of fossil fuels—have increased CO₂ concentrations, leading to an enhanced greenhouse effect and global warming.314