The correct option is They are better absorbers of long wave radiations..
Explanation
The effectiveness of a greenhouse gas in contributing to global warming is determined by its Global Warming Potential (GWP). This metric depends primarily on two factors: the gas's radiative efficiency (its ability to absorb energy) and its atmospheric lifetime. While Carbon Dioxide ($CO_2$) is the reference gas with a GWP of 1, other gases like Methane ($CH_4$) and Nitrous Oxide ($N_2O$) are significantly more potent on a per-molecule basis.
Detailed Analysis:
- They are present in larger quantities. is Incorrect: Carbon Dioxide is present in the atmosphere in much larger quantities (measured in parts per million, or ppm) compared to Methane and Nitrous Oxide (measured in parts per billion, or ppb). Therefore, abundance is not the reason for their higher per-molecule effectiveness.
- They are better absorbers of long wave radiations. is Correct: Methane and Nitrous Oxide are chemically more effective at trapping heat than Carbon Dioxide. Their molecular structures allow them to absorb long-wave terrestrial radiation (infrared radiation emitted by the Earth) more efficiently. For instance, Methane has a GWP approximately 28 times higher than $CO_2$ over a 100-year period, and Nitrous Oxide has a GWP approximately 265-298 times higher, primarily due to this superior absorption capability.
- They reflect solar radiation more effectively. is Incorrect: The greenhouse effect is caused by the absorption and re-emission of outgoing long-wave radiation, not the reflection of incoming solar (short-wave) radiation. Reflection of solar radiation (albedo effect) generally leads to cooling, not warming.
- They destroy the ozone layer. is Incorrect: While Nitrous Oxide is a dominant ozone-depleting substance, this characteristic is separate from its role as a greenhouse gas. Ozone depletion involves stratospheric chemistry, whereas the greenhouse effect involves the trapping of heat in the troposphere.
Key Takeaway:
Gases like Methane and Nitrous Oxide have a higher Global Warming Potential (GWP) than Carbon Dioxide because they are more efficient absorbers of long-wave infrared radiation per molecule, despite their lower atmospheric concentrations.