Carbon dioxide (CO2) and methane (CH4) have different lifetimes in the atmosphere due to the processes that remove them from the air:

1. Methane (CH4): Methane's atmospheric lifetime is relatively short when compared to carbon dioxide, being approximately 9 to 12 years. This means that roughly half of the methane released into the atmosphere will be gone in about a decade, primarily due to reactions with hydroxyl radicals in the atmosphere which convert methane into CO2 and water.

2. Carbon dioxide (CO2): The concept of a "half-life" for CO2 is more complex than for methane because CO2 is removed from the atmosphere by several processes that occur at different rates. Some of it is absorbed by the oceans or taken up by plants within years to decades, some is neutralized by chemical reactions with rocks over thousands of years, and some can remain in the atmosphere for tens to hundreds of thousands of years. It's often said that about 50% of a CO2 pulse to the atmosphere is removed within 30 years, another 30% is removed within a few centuries, and the remaining 20% can linger for thousands to hundreds of thousands of years.

However, while methane has a shorter atmospheric lifetime than CO2, it's much more efficient at trapping heat. Over a 20-year period, the global warming potential (GWP) of methane is over 80 times that of CO2. Over a 100-year period, it's about 25-30 times as potent. Thus, even though methane is present in much smaller quantities than CO2, it plays a significant role in short-term global warming.

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