Methane is ______ times more active GHG gas compared to carbon dioxide.   15 17 19 21

To determine how many times methane is more active as a greenhouse gas (GHG) compared to carbon dioxide, we can refer to the global warming potential (GWP) values commonly used in climate science.

1. GWP of Methane: The GWP of methane (CH₄) is approximately 28-36 times that of carbon dioxide (CO₂) over a 100-year period, depending on the source.

2. GWP of Carbon Dioxide: The GWP of carbon dioxide is defined as 1, as it is the baseline for comparison.

Considering the options provided (15, 17, 19, 21), the closest commonly cited value to the GWP of methane is around 21 based on certain assessments.

Final Answer

Methane is 21 times more active as a greenhouse gas compared to carbon dioxide.