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When sunlight reaches Mars, it warms the surface, which then emits infrared radiation back into space. Greenhouse gases—primarily CO₂—are transparent to visible light but absorb infrared, creating a blanket that keeps heat from escaping. The result is a subtle warming that, on Earth, raises temperatures by about 33 °C (93 °F).
Mars’s atmosphere is dominated by carbon dioxide (over 95 % by volume). The remainder is mainly nitrogen, argon, oxygen, and trace carbon monoxide. Though CO₂ is an effective greenhouse agent, the thinness of the Martian air—roughly 1 % of Earth’s atmospheric pressure—means the greenhouse effect is exceedingly weak.
In 1971 the Mariner 9 mission observed a dramatic temperature rise during a planet‑wide dust storm, demonstrating that short‑term aerosol loading can temporarily trap heat. Astronomer Carl Sagan noted that, under the right conditions, such warming could melt polar ice caps. The CO₂ clouds that form when the planet is heated would thicken the atmosphere, potentially creating a feedback loop that further raises surface temperatures. Some researchers speculate that similar episodes may have occurred billions of years ago, possibly sustaining a warmer climate in Mars’s early history.
Given the present weak greenhouse effect, scientists are exploring ways to warm Mars artificially. One proposal is to release additional CO₂ from the polar caps to thicken the atmosphere, thereby amplifying the greenhouse warming. The exact amount required is uncertain because the total CO₂ reservoir in the caps remains poorly constrained. Alternative ideas include injecting potent greenhouse gases such as perfluorocarbons (PFCs), which have a higher global‑warming potential than CO₂ but would need to be delivered in vast quantities.
