Question

Which of the following is not a greenhouse gas? (a) water vapour (b) \(\mathrm{CO}_{2}\) (c) \(\mathrm{O}_{2}\) (d) \(\mathrm{CH}_{4}\)

Short answer

(c)  ext{O}_{2} ight is not a greenhouse gas.

Step-by-step solution

Understanding Greenhouse Gases

Greenhouse gases are those that trap heat in the Earth's atmosphere, contributing to the greenhouse effect. Common examples are carbon dioxide ( ext{CO}_{2} ight), methane ( ext{CH}_{4} ight), and water vapor. They allow sunlight to enter the atmosphere freely but prevent the heat from leaving the atmosphere, thus warming the planet.

Identify Non-Greenhouse Gases

In the given options, we need to identify the gas that does not contribute to the greenhouse effect. Among the options listed - water vapor,  ext{CO}_{2} ight, and  ext{CH}_{4} ight are known greenhouse gases.

Evaluating  ext{O}_{2} ight

 ext{O}_{2} ight (oxygen) is essential for life and combustion but is not considered a greenhouse gas. It does not significantly trap heat in Earth's atmosphere or contribute to the greenhouse effect.

Conclude the Answer

Since  ext{O}_{2} ight does not contribute to trapping heat in the atmosphere like the other gases listed, it is the correct answer to the question of which is not a greenhouse gas.

Key concepts

Greenhouse Effect

The greenhouse effect is a natural process that warms the Earth’s surface. When the Sun’s energy reaches the Earth, part of it is reflected back to space and the rest is absorbed, warming the planet. The Earth emits energy back towards space, and some of this energy is trapped by greenhouse gases in the atmosphere, which keeps the planet at a habitable temperature.

• The greenhouse effect is essential for life on Earth. Without it, our planet would be too cold for humans, plants, and animals.
• Greenhouse gases act like a blanket, retaining heat and keeping the Earth warm.
• This effect is intensified by human activities that increase greenhouse gases in the atmosphere, leading to global warming.

Carbon Dioxide

Carbon dioxide \( \mathrm{CO}_{2} \) is a colorless, odorless gas found naturally in Earth's atmosphere. It plays a significant role in the greenhouse effect.

• It is released through natural processes such as respiration and volcano eruptions and by human activities like deforestation and burning fossil fuels.
• While \( \mathrm{CO}_{2} \) is necessary for photosynthesis, in excess, it contributes to the warming of the planet.
• The concentration of carbon dioxide has increased significantly since the industrial revolution, raising concerns about climate change.

Methane

Methane \( \mathrm{CH}_{4} \) is another potent greenhouse gas, even more effective at trapping heat in the atmosphere than carbon dioxide, although it is present in smaller quantities.

• Methane is released through both natural sources like wetlands and man-made sources such as agriculture (cattle emissions) and fossil fuel extraction.
• Its heat-trapping ability makes it a significant contributor to climate change, though it remains in the atmosphere for a shorter period than \( \mathrm{CO}_{2} \).
• Mitigating methane emissions can be an effective short-term strategy to slow down global warming.

Water Vapor

Water vapor is the most abundant greenhouse gas, and it plays a critical role in the natural greenhouse effect.

• As water vapor increases, it can amplify the warming caused by other greenhouse gases through a process called positive feedback.
• This is because warmer air holds more moisture, and thus more water vapor results in more heat being trapped.
• Human activities do not directly add significant amounts of water vapor to the atmosphere, but increased temperatures from other gases increase its concentration.

Oxygen

Oxygen \( \mathrm{O}_{2} \) is vital for life on Earth, but unlike other gases mentioned, it is not considered a greenhouse gas.

• It does not significantly trap heat or contribute to the greenhouse effect.
• Oxygen is crucial for respiration in humans and animals and is important for the process of combustion.
• While it does not contribute to climate change, preserving oxygen levels requires maintaining healthy ecosystems.