Ever wondered how paleoclimate research arrives at˚C estimates for eras millions of years ago? I did. And here's the answer. In 16 minutes. Very efficient, me likes.
Related to a set standard is: amount of heavy isotopes (w/ more neutrons) in molecules.

I'll add more tweets as I figure out the answer to my original question that set me on this quest:
. @niwa_nz monitors δ13CO2 ratio to 12CO2, heavy vs light isotope https://niwa.co.nz/atmosphere/our-data/trace-gas-plots/carbon-dioxide# It decreases, but lately, the rate of decrease has slowedAnd that's my quest for today

A bit of the first confusion over the graph and text by NIWA has lifted. ATM, I interpret the graph as depicting a decreasing number of 13CO2 in the atmosphere, atmo, compared to 12CO2.

But it might be the exact oppositeAs the video says: ++˚C = ++heavy isotopes in the atmo.

Whether the decreasing curve means --13CO2 or ++13CO2, I'll find out. But the slowdown has happened before. Between 2007 and 2011. Tho, it's got nothing to do with CO2 rise.

That timespan of 5 years corresponds to the CH4 curve flattening for 7 years until 2007. A late reaction?

Plants don't use much 13CO2. Some use -26‰ 13CO2, some -12‰.

Another factor is CH4. Which contains very little 13C: biogenic -60‰ and thermogenic -40‰. Thermo. is fossil gas; while bio. is cow burps or what comes up from landfills or rice fields.
--13CO2 w/ more ff-gas?

As I progress in my quest (I hope), I turn to the Paleocene–Eocene Thermal Maximum, PETM: a sudden 5-8˚C rise, lasting 200k yrs 55mio yrs ago, with a corresponding spike in δ13C found in proxies(probes).

I take it as 1 reason why IPCC invented RCP8.5, the high emissions scenario

Off-topic: I like RCP8.5. It's an extreme and extremes trigger our curiosityLike the extreme flattening of 13CO2 triggered mine. W/o it, I'd not have gone on today's quest.
A similar trigger might've caused scientists to look @ climate refugees in RCP8.5 https://twitter.com/anlomedad/status/1219198171076857857

Anyway. I take the heated debate around RCP8.5 as a sign for hubris in those opposing it. They're wantonly blind to its various benefits, eg relating paleoclimate research to contemporary impact research and the trigger / the psychology of research.
Or they drive a hidden agenda.

Back on topic https://twitter.com/anlomedad/status/1254300800064598017 IMO, the downward trend does mean: less 13CO2 or more 12CO2. Or both.
Why then was/is the curve flattening? What drives the trend? Seems counter intuitive in a warming climate bc warmer oceans release the heavier 13CO2 with increasing ease.

Are oceans warming? Yes, with regional differences. The pic shows ˚C on April 25 https://www.ospo.noaa.gov/Products/ocean/sst/contour/
the ˚C scale is -2 to 31.7˚C.
At https://www.ncdc.noaa.gov/cag/global/time-series/nhem/ocean/all/12/1998-2020 we see hemispheric monthly sea surface ˚C anomalies from 1998-2020 which can be related to the 13CO2 plot from NIWA

Tried to correlate the 3 notable 13CO2 phases with hemispheric temp anomalies. What do you say? Is the rate change conclusive with sea surface temperature changes? I don't see it. At least not considering rate of decrease and the profoundly differing temperature rises as circled

If the NIWA plot marks the beginning of each year and not mid-year (hope so), then the ENSO months don't correspond conclusively with 13CO2, either. Btw, clips with El Nino, El Nina months, and a clip of the total time series from 2003-2010 in this thread https://twitter.com/anlomedad/status/1254509352226107392

I see dips in˚C that don't show in the 13CO2 plot. So if the 13CO2 plateau from Oct 2017 -June 2019(ff?) is not all due to sea surface temperature, what other reasons can I think of?

1) + 13CO2 = eg volcanic or clathrate
2) + 13CO2 = eg ff CH4
3) - 12CO2 via plant more uptake

2) + 13CO2 =eg fossil CH4.
If fossil CH4 were the source, it wd be thermogenic CH4 released ~ 12 years earlier, and by 2017, when the plateau sets in, be transformed into 13CO2 and water. Ie emitted <= 2005. The other 13CO2 plateau at 2007-09 got emitted ~ 1997. Does it fit? Nope

(Sorry for the graphs. It's not MS Paint, I swear)

Superficially, it looks like a fit. But a slowdown of the 13CO2 decrease rate needs a steep rise in ff CH4 ~ 12 yrs prior. I can't see that.
And would tiny amounts of ppbillion versus ppmillion make a dent? I guess not.

Hm.

The eruption of Pinatubo 1991 could have released heavy CH4. NOAA's CH4 data show 1990-91 are a little higher with the occasional CH4 increase of 1.5 ppb/month. But it's a short stint in an otherwise rather even growth of ~ <= 1ppb /month.

ff CH4 is outNow to option 1) and 3).