The Carbon Isotope Fingerprint Just Got Smudged – and I Owe Some of You an Apology
13 hours ago Charles Rotter
In light of the recent Nature study I discussed yesterday in Settled Science Springs a Leak, it’s time to revisit a position I’ve long held—and, it turns out, one that now requires correction. Specifically, the long-standing assumption that carbon isotope ratios (δ¹³C and Δ¹⁴C) provide unambiguous proof that the rise in atmospheric CO2 is almost entirely anthropogenic.
For years, I’ve maintained that anyone challenging the anthropogenic origin of the CO2 increase had to address the isotope fingerprint argument before their work could be taken seriously. Submissions that didn’t engage with the Δ¹⁴C or δ¹³C evidence were declined, often with little further discussion. That confidence, I now recognize, was misplaced.
The recent study, Old carbon routed from land to the atmosphere by global river systems, has fundamentally altered the context in which the isotopic attribution arguments operate. According to the authors, 59% of global riverine CO2 emissions are sourced from old carbon, meaning millennial-aged carbon from deep soils, sediments, or rock weathering—not recently photosynthesized biomass.
These emissions are radiocarbon-dead, lacking the Δ¹⁴C signal, and are often depleted in δ¹³C—precisely the isotopic traits long attributed to fossil fuel combustion. Until now, these natural contributions were omitted from carbon cycle models and largely absent from attribution logic.
https://wattsupwiththat.com/2025/06/17/the-carbon-isotope-fingerprint-just-got-smudged-and-i-owe-some-of-you-an-apology/
