Question

Consider a layer of atmosphere where temperature increases with height. If the concentration of a vertically well-mixed greenhouse gas suddenly increases in this layer, then an immediate consequence is that:

• A. infrared radiation leaving the top of the layer decreases.
• B. infrared radiation leaving the top of the layer increases.
• C. infrared radiation leaving the top of the layer remains unchanged.
• D. the layer becomes optically thinner to infrared radiation.

Hint:

When greenhouse gases increase in concentration, they increase the atmosphere's capacity to absorb and emit infrared radiation. This results in higher infrared radiation being emitted from the top of the layer.

Answer 1

The Correct Option is B

In this question, we are asked to analyze the immediate consequences of a sudden increase in the concentration of a vertically well-mixed greenhouse gas in the atmosphere. We are given that the temperature in this atmospheric layer increases with height. The question specifically focuses on the infrared radiation leaving the top of the layer.
Understanding the Concept:
1. Greenhouse Effect: Greenhouse gases, such as carbon dioxide (CO\(_2\)), methane (CH\(_4\)), and water vapor (H\(_2\)O), absorb infrared radiation (heat) emitted from the Earth's surface and re-radiate it in all directions, including back toward the Earth's surface. This process traps heat within the atmosphere and contributes to the greenhouse effect, increasing the overall temperature of the atmosphere.
2. Impact of an Increase in Greenhouse Gas Concentration: When the concentration of a well-mixed greenhouse gas (e.g., CO\(_2\)) suddenly increases in the atmosphere, the immediate effect is that the layer of atmosphere becomes more opaque to infrared radiation. The enhanced greenhouse gas concentration means that more infrared radiation is absorbed and trapped within the atmosphere. This leads to an increase in the radiation emitted from the top of the layer.
3. Energy Balance and Infrared Radiation: For a given layer of atmosphere, the energy balance depends on the absorption and emission of infrared radiation. A higher concentration of greenhouse gases causes the layer to absorb more radiation at lower levels and re-emit it at higher levels. Hence, the infrared radiation leaving the top of the layer increases as the gases absorb and emit more radiation.
Therefore, the correct answer is option (B) because the immediate consequence of increasing the concentration of a greenhouse gas in a well-mixed atmospheric layer is an increase in the infrared radiation leaving the top of the layer.
Conclusion:
The correct choice is (B): Infrared radiation leaving the top of the layer increases. This is because the increased greenhouse gas concentration enhances the ability of the atmosphere to absorb and re-radiate infrared radiation.