Do rising methane levels herald a climate feedback loop?

livemint.com:

methane emissions, Dr Nisbet worries that the Earth’s natural systems may be churning out more and more of the gas. Methane levels are certainly rising. Over the 40 years during which the gas’s level in the atmosphere has been monitored, it has grown by about 17%, in two distinct stages.

In the first, strong annual growth slowed until, in the early 2000s, it stopped altogether. But around 2006 it began growing again—and the rate is accelerating. The evidence that wetlands might be to blame comes from the type of methane being emitted.

Methane is made of four atoms of hydrogen atoms and one of carbon. That carbon atom can be either the “light" isotope, with six neutrons in its nucleus, or the heavy isotope, which has seven. Methane-making bacteria find the lighter sort easier to handle.

The methane they produce is therefore lighter than methane from fossil fuels or forest fires, another major source of the gas. And over the past 15 years the methane in the atmosphere has indeed become lighter. That is suggestive, but not conclusive.

Accounting for the methane in the air is tricky. An academic collaboration called the Global Methane Budget (GMB) produces two tallies. One bottom-up estimate adds the emissions of all known sources.

Another top-down one works backwards from the methane levels in the air and tries to calculate emissions on the ground consistent with it. In the most recent budget, published in 2020, the two approaches disagreed significantly. The total calculated from known sources was 30% higher than the number derived from the atmosphere.