Methane is roughly 30 times more potent as a Greenhouse Gas than CO2. Over the last 30 years, the measured levels in the atmosphere have been steadily rising, - maintaining a clearly defined seasonal cycle. 1900 parts per billion (ppb) was reached in November 2018 - the highest level in 800,000 years.
“Methane is an important greenhouse gas, responsible for about 20% of the warming induced by long-lived greenhouse gases since pre-industrial times. By reacting with hydroxyl radicals, methane reduces the oxidizing capacity of the atmosphere and generates ozone in the troposphere. Although most sources and sinks of methane have been identified, their relative contributions to atmospheric methane levels are highly uncertain.”
Source: Three decades of global methane sources and sinks, Nature Geoscience, 2013
As noted above, reactions with hydroxyl radicals are foremost in 'sinks' for methane - but their production is unclear.
The most important sink in the methane cycle is reaction with the hydroxyl radical, which is produced photochemically in the atmosphere. Production of this radical is not fully understood and has a large effect on atmospheric concentrations.
More info at: Wikipedia
The balance between sources and sinks of methane is not yet fully understood. The IPCC Working Group I stated in chapter 2 of the Fourth Assessment Report that there are “large uncertainties in the current bottom-up estimates of components of the global source”, and the balance between sources and sinks is not yet well known.
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