" Net Isotopic Signature of Atmospheric CO2 Sources and Sinks: No Change since the Little Ice Age
by Demetris Koutsoyiannis [ORCID]

Recent studies have provided evidence, based on analyses of instrumental measurements of the last seven decades, for a unidirectional, potentially causal link between temperature as the cause and carbon dioxide concentration ([CO2]) as the effect. In the most recent study, this finding was supported by analysing the carbon cycle and showing that the natural [CO2] changes due to temperature rise are far larger (by a factor > 3) than human emissions, while the latter are no larger than 4% of the total. Here, we provide additional support for these findings by examining the signatures of the stable carbon isotopes, 12 and 13. Examining isotopic data in four important observation sites, we show that the standard metric δ13C is consistent with an input isotopic signature that is stable over the entire period of observations (>40 years), i.e., not affected by increases in human CO2 emissions. In addition, proxy data covering the period after 1500 AD also show stable behaviour. These findings confirm the major role of the biosphere in the carbon cycle and a non-discernible signature of humans."

https://www.mdpi.com/2413-4155/6/1/17

He uses isotopic data from Scripps Institute.

Poor JM. Just can't help himself. If it is  not Milankovitch cycles it must be human.

Polyphemus wrote on Apr 10^th, 2024 at 5:00pm:


Well, as JM freely admits there has been global brightening due to various Clean Air Acts. That means there are less particulates, less pollution, so the Sun is not reduced by those particulates. Therefore, we have global warming. So it could be said that the Clean Air Acts, have indeed promoted AGW.