As an expert in atmospheric sciences, I have a deep understanding of the various gases that play a role in the Earth's climate system. Greenhouse gases, as you've correctly stated, are those that absorb and emit radiant energy within the thermal infrared range, contributing to the greenhouse effect. This effect is a natural process that helps to maintain the Earth's temperature at a level suitable for life. However, the excessive emission of certain gases due to human activities has led to an enhanced greenhouse effect, which is a significant concern in the context of global warming.

The primary greenhouse gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). These gases have different heat-trapping capabilities and atmospheric lifetimes. For instance, water vapor is the most abundant greenhouse gas and has a short atmospheric lifetime, while carbon dioxide has a longer atmospheric lifetime and is the primary focus of climate change mitigation efforts due to its direct link with human activities such as burning fossil fuels.

However, not all gases contribute to the greenhouse effect to the same extent, and some are not classified as greenhouse gases despite having some heat-trapping properties. For example, oxygen (O2) and nitrogen (N2) are the most abundant gases in the Earth's atmosphere, making up approximately 21% and 78% of the atmosphere by volume, respectively. Neither of these gases has a significant greenhouse effect due to their molecular structure and lack of ability to absorb infrared radiation effectively.

Another gas that is not typically classified as a greenhouse gas is argon (Ar), which is a noble gas that makes up about 0.93% of the Earth's atmosphere. Argon is chemically inert and does not react with other substances to form compounds. Its molecular structure does not allow it to absorb infrared radiation in a way that would contribute to the greenhouse effect.

It's important to note that while these gases may not be considered greenhouse gases, they still play vital roles in the Earth's atmosphere and ecosystem. For example, oxygen is essential for aerobic respiration in most living organisms, and nitrogen is a key component of amino acids and nucleic acids, which are the building blocks of life.

In conclusion, while there are several gases in the Earth's atmosphere, not all of them are known as greenhouse gases. The classification depends on their ability to absorb and emit infrared radiation within the thermal infrared range. Oxygen, nitrogen, and argon are examples of gases that, despite being present in significant quantities in the atmosphere, are not considered greenhouse gases due to their molecular properties and lack of contribution to the greenhouse effect.

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A greenhouse gas is a gas in an atmosphere that absorbs and emits radiant energy within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone.read more >>