Atmospheric lifetime
A measure of how long a substance remains in the atmosphere before removal or chemical transformation.
Example
Methane has an atmospheric lifetime of roughly a decade, making sustained emission cuts relevant to near-term warming.
The catch
A lifetime is a statistical measure; molecules do not disappear together on a fixed date.
Related terms
Methane, Albedo, Carbon budget, Carbon dioxide, Climate change, Climate feedback
In more depth
Atmospheric lifetime, explained.
Atmospheric lifetime decides how quickly a gas's concentration responds when emissions change. Methane, with a lifetime of about 12 years, is destroyed mainly by the hydroxyl radical, a reactive molecule often called the atmosphere's detergent. Cut methane emissions and its concentration starts to fall within years, a property that earns it the label short-lived climate pollutant.
Carbon dioxide has no comparable single figure. Oceans and plants absorb much of each release over decades to centuries, yet a portion stays in the air for millennia. That difference shapes climate targets. Steady methane emissions hold methane's concentration roughly level, while steady CO₂ emissions keep adding to the stock, so CO₂ has to reach net zero before the warming it causes stops rising.