Final answer:
Methane is approximately 28 times more potent as a greenhouse gas than carbon dioxide over a 20-year period due to its higher global warming potential, despite its shorter atmospheric lifespan.
Step-by-step explanation:
The potential of methane (CH4) to contribute to the greenhouse effect, compared to carbon dioxide (CO2), is measured in terms of global warming potential (GWP). Over a 20-year period, methane is significantly more potent than CO2. Methane has a GWP approximately 28 times greater than that of CO2, meaning that it is 28 times more effective at absorbing infrared radiation. However, methane does not stay in the atmosphere as long as CO2. Therefore, the GWP over a longer period, such as 100 years, is lower for methane compared to its 20-year GWP.
Despite methane being present in smaller quantities in the atmosphere than CO2, it still contributes significantly to the enhanced greenhouse effect due to its high effectiveness per molecule. Human activities have led to a 2.5-fold increase in atmospheric methane since the industrial era, contributing about 20 percent of the enhanced greenhouse effect.