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1 Water vapor. 2  The most abundant greenhouse gas, but importantly, it acts as a feedback to the climate. 3  Water vapor increases as the Earth's atmosphere warms, but so does the possibility of clouds and precipitation, making these some of the most important feedback mechanisms to the greenhouse effect.
The most abundant gases in the atmosphere are nitrogen at 78 percent and oxygen at 21 percent, while the trace gases methane, neon and helium make up around one-tenth of 1 percent of the atmosphere. Oxygen, nitrogen and argon are classified as permanent gases because their percentages always remain the same.