Methane is a powerful greenhouse gas, and is responsible for about a quarter of the warming we have experienced to-date. Reducing methane emissions is an important part of climate mitigation. Its also important to understand that methane is very different from CO2.

A thread: 1/9

When we emit a ton of methane (CH4), about 80% is removed from the atmosphere via chemical reactions with hydroxyl (OH) radicals within 20 years. CO2, on the other hand, is not removed by chemical reactions; it has to be absorbed by land and ocean sinks. 2/9

Forty years after its been emitted nearly all methane is gone, while nearly 50% of the CO2 remains in the atmosphere (assuming current carbon sink behavior; a warming world will likely reduce the efficacy of the carbon sink resulting in more CO2 remaining in the atmosphere). 3/9

In practice, this means that the long-term atmospheric CO2 concentration is a function of cumulative emissions, while atmospheric CH4 is a function of the rate of emissions. One ton per year of CO2 increases atmospheric CO2 by ~40 tons by 2100. For methane its only 12 tons. 4/9

To put it another way, if we stop increasing CH4 emissions, atmospheric CH4 will stop increasing. But if we stop increasing CO2 emissions atmospheric CO2 will continue to increase until we reduce CO2 emissions close to zero. 5/9

This raises a few important points:

First, CO2 is the primary driver of longer-term warming. In future baseline emissions scenarios (e.g. where we don't mitigate emissions) CO2 drives around 90% of the additional 21st century warming. 6/9

Second, reducing warming by cutting methane is a lot easier than CO2. Cutting methane results in near-immediate temperature declines, while cutting CO2 only slows the rate of warming until you go to near-zero. 7/9

Third, methane can be cut at any point and have a large effect on temperatures. CO2 on the other hand is cumulative; waiting to cut CO2 emissions locks in warming in a way thats not the case for methane. 8/9

Finally, the prioritization of CO2 and CH4 mitigation depends on short-term vs long-term prioritization. If you think we are close to climate tipping points CH4 cuts are a way to quickly reduce warming. If you care more about 2050 or 2070 temps than CO2 cuts matter more. 9/9

I have a follow-up thread with a simple example (cows vs coal!) for folks who are interested: https://twitter.com/hausfath/status/1230929548880969728 10/9