Final answer:
The amount of CH₄ (methane) in ppm that saturates its absorption band like CO₂ is less than 280 ppm, but the exact value is not specified.
Step-by-step explanation:
The question is asking for the amount of CH₄ (methane) in parts per million (ppm) that it takes before its absorption band begins to saturate like CO₂ (carbon dioxide).
Based on the information provided, the saturation point of the CO₂ absorption band is not specifically stated. However, it is mentioned that CO₂ concentration has fluctuated between 180-280 ppm in the past, reaching the higher end of the range during warmer periods. Hence, we can assume that the CO₂ absorption band is not saturated at 280 ppm, which is at the upper limit of the mentioned range.
Therefore, the answer to the question is less than 280 ppm for CH₄ to reach a saturation point similar to CO₂, but the exact ppm value is not specified.