Friday, June 21, 2024
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Greenhouse Gas Lifetimes

This graph represents the persistence, or lifetime, of greenhouse gases in the atmosphere. The Y axis is the fraction of the original “impulse” that remains, while the X axis shows time in years.* Suppose you were to release 1 gigatonne of CO₂ (GtCO₂). At that moment (year 0) 1 GtCO₂ would be in the atmosphere. Each year thereafter, some of that CO₂ would be eliminated. After 20 years, for example, only 0.6 GtCO₂ would remain.

CO₂ is primarily eliminated from the atmosphere by plants, which use it for photosynthesis, and by absorption in the ocean. Still CO₂ is a is a relatively stable molecule. Set the years slider to 1,000 and you will see that even a millennium later, about 24% of it remains in the atmosphere.

Methane, on the other hand, breaks down relatively quickly. As it circulates in the atmosphere, a series of chemical reactions transform it into other molecules including CO₂. After only a decade or two, most of it is gone.

If you’d like to examine it in more detail, the parameters and equations used to calculate the “impulse response functions” for these gases comes from the IPCC here, here, and here.

*Because the Y axis represents a fraction remaining, changing the absolute amount of gas released in the slider on the left will not change the graph.


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