The treatment of all greenhouse gases as “CO2-equivalent”, using a metric known as global warming potential (GWP).
This misrepresents the impact of short-lived climate pollutants, such as methane, on future warming.
Drew Shindell, a NASA climate scientist, believes that, while methane dissipates faster than carbon dioxide, it is easier to deal with right now.
“Success in controlling CO2 emissions is likely to make very little difference on temperature over the next 40 years,” he says.
CO2 life-span, there is still no consensus.
Is it 5, 12, ..... 100 years?
It is true that an individual molecule of CO2 has a short live time in the atmosphere.
However, in most cases when a molecule of CO2 leaves the atmosphere it is simply swapping places with one in the ocean.
Thus, the warming potential of CO2 has very little to do with the live time of CO2.
What really governs the warming potential is how long the extra CO2 remains in the atmosphere.
CO2 is essentially chemically inert in the atmosphere and is only removed by biological uptake and by dissolving into the ocean.