Why is the relative concentration of atmospheric carbon-13 decreasing?

The drop seems to rule out fossil fuel emissions, wildfires, or biomass cook stoves as the reason for the post-2007 methane surge. All those sources of methane, to a greater or lesser extent, are enriched in carbon-13, not depleted.

It’s a counterintuitive finding: methane from fossil fuels seems to be making up a smaller share of total global emissions. The decline in the 13-C isotope of methane in the atmosphere indicates that microbial sources must have an increasing share of total methane emissions globally.

From https://www.climate.gov/news-features/understanding-climate/after-2000-era-plateau-global-methane-levels-hitting-new-highs

mollwollfumble said:

Why is the relative concentration of atmospheric carbon-13 decreasing?

The drop seems to rule out fossil fuel emissions, wildfires, or biomass cook stoves as the reason for the post-2007 methane surge. All those sources of methane, to a greater or lesser extent, are enriched in carbon-13, not depleted.

It’s a counterintuitive finding: methane from fossil fuels seems to be making up a smaller share of total global emissions. The decline in the 13-C isotope of methane in the atmosphere indicates that microbial sources must have an increasing share of total methane emissions globally.

From https://www.climate.gov/news-features/understanding-climate/after-2000-era-plateau-global-methane-levels-hitting-new-highs

That is very interesting, or the actual rise in overall methane levels even more so.

The drop in 13-C levels might be the mixing of methane from various quarters, which have naturally reduced levels of 13-C or none at all.

These devoid levels of 13-C methane is largely from increased farm production, due to dramatically increased human population and from natural wetlands. In the latter situation drying occurs from droughts, permitting vegetation to grow in previously flooded areas, but then that dies to release higher methane levels when flooded again. Obviously less stable climate conditions, droughts and floods will be enhanced, especially in tropical and mid-level geographic regions where these higher methane levels are greatest. I would think as more permafrost melts (as is the case), it will only exacerbate the problem.

PermeateFree said:

mollwollfumble said:

Why is the relative concentration of atmospheric carbon-13 decreasing?

The drop seems to rule out fossil fuel emissions, wildfires, or biomass cook stoves as the reason for the post-2007 methane surge. All those sources of methane, to a greater or lesser extent, are enriched in carbon-13, not depleted.

It’s a counterintuitive finding: methane from fossil fuels seems to be making up a smaller share of total global emissions. The decline in the 13-C isotope of methane in the atmosphere indicates that microbial sources must have an increasing share of total methane emissions globally.

From https://www.climate.gov/news-features/understanding-climate/after-2000-era-plateau-global-methane-levels-hitting-new-highs

That is very interesting, or the actual rise in overall methane levels even more so.

The drop in 13-C levels might be the mixing of methane from various quarters, which have naturally reduced levels of 13-C or none at all.

These devoid levels of 13-C methane is largely from increased farm production, due to dramatically increased human population and from natural wetlands. In the latter situation drying occurs from droughts, permitting vegetation to grow in previously flooded areas, but then that dies to release higher methane levels when flooded again. Obviously less stable climate conditions, droughts and floods will be enhanced, especially in tropical and mid-level geographic regions where these higher methane levels are greatest. I would think as more permafrost melts (as is the case), it will only exacerbate the problem.

An increased number of microbes doesn’t have to be an increase in farm production. But I agree that that’s the most likely. It could also be an increase in native forest production, I think.

Some other environmentally aware people were apt to blame clathrates, but farm seems more likely to me.

mollwollfumble said:

PermeateFree said:

mollwollfumble said:

Why is the relative concentration of atmospheric carbon-13 decreasing?

The drop seems to rule out fossil fuel emissions, wildfires, or biomass cook stoves as the reason for the post-2007 methane surge. All those sources of methane, to a greater or lesser extent, are enriched in carbon-13, not depleted.

It’s a counterintuitive finding: methane from fossil fuels seems to be making up a smaller share of total global emissions. The decline in the 13-C isotope of methane in the atmosphere indicates that microbial sources must have an increasing share of total methane emissions globally.

From https://www.climate.gov/news-features/understanding-climate/after-2000-era-plateau-global-methane-levels-hitting-new-highs

That is very interesting, or the actual rise in overall methane levels even more so.

The drop in 13-C levels might be the mixing of methane from various quarters, which have naturally reduced levels of 13-C or none at all.

These devoid levels of 13-C methane is largely from increased farm production, due to dramatically increased human population and from natural wetlands. In the latter situation drying occurs from droughts, permitting vegetation to grow in previously flooded areas, but then that dies to release higher methane levels when flooded again. Obviously less stable climate conditions, droughts and floods will be enhanced, especially in tropical and mid-level geographic regions where these higher methane levels are greatest. I would think as more permafrost melts (as is the case), it will only exacerbate the problem.

An increased number of microbes doesn’t have to be an increase in farm production. But I agree that that’s the most likely. It could also be an increase in native forest production, I think.

Some other environmentally aware people were apt to blame clathrates, but farm seems more likely to me.

Well that was what the article you supplied said, which was written and produced by climate-education@noaa.gov which seems to be a highly professional organisation. And yes, I did read it all. I just changed the emphasis to the increasing methane record from your OP.