We recently reported on an important new study that raises interesting questions about where the extra carbon in the atmosphere is coming from. And we noted in passing that geochemist Dr. Matthew Wielicki has written a Substack essay about this issue called “Is it really our CO2”? His essay deserves a deeper look because the fundamental question is very interesting and very relevant. The Earth’s annual carbon cycle is massive, and our CO2 emissions make up only a tiny fraction of the flows into and out of the atmosphere. Some of the flows in and out are poorly measured. So how do we know the rising CO2 content of the atmosphere is due to humans rather than to natural sources? The answer up to now has been that CO2 coming from natural sources has an atomic fingerprint that differs from the stuff we get from burning fossil fuels. On average the CO2 in the air is gradually becoming more like the fossil fuel-based stuff which means the increase is likely due to us. But scientists recently discovered that a large natural source, namely rock erosion by rivers, releases a lot of CO2 that looks exactly like the fossil fuel-based stuff. The models tracking where the carbon in the air is coming from don’t take this into account. Which means we may have to rethink the whole question of how much we are responsible for changing the atmosphere’s CO2 content.
The fundamental issue has to do with the term “fossil” in fossil fuels. (And never mind the idiots who think it means anyone believes oil came from dinosaurs.) These hydrocarbons are ancient: millions of years in the making. Which is a long time by any standard including that of radioactive decay of various elements in the periodic table including, crucially here, carbon.
The standard chemistry class carbon atom, item #6 on the periodic table, has the standard setup with six electrons, six protons and six neutrons. Boooring! But of course it also has less standard forms (“isotopes”) that have a matched number of electrons and protons so the electric charges cancel out but differ based on the number of neutrons lurking in the nucleus. The more neutrons the more unstable the atomic structure, aka the more “radioactive” the element, and the shorter the “half life” in which half of any given isotope will spew forth its extra neutrons and go straight. (With nuclear fission the atomic nucleus actually splits into two or more elements different from the original but with radioactive decay it just changes from one isotope to another.) And what interests us here particularly are 14C (with eight neutrons and six protons, hence the 14) and 13C (with, obviously, one extra neutron so seven plus the usual six protons).
Crucially, normal carbon gets turned into one of its isotopes by being bombarded by cosmic rays that among other things contain stray neutrons looking to invade someone’s nucleus. So the stuff gets made naturally and decays naturally. But it only gets made if it’s exposed to the sun, not if it’s buried deep underground for a long time. There it just decays.
So over millions of years the 14C isotopes in oil and coal have decayed entirely into 12C and the 13C have partially decayed, leaving a higher fraction of those with 12. Which is meant to be the crucial “fingerprint” of a given cloud of carbon dioxide being the result of humans burning fossil fuel and releasing a very high proportion of 12C, a bit of 13C and no 14C, whereas young nice natural CO2, such as that released by decaying plants, still has abundant 14C and 13C.
Science has established that in recent decades not only has the overall CO2 content of the air risen, but the fraction with 14C and 13C has fallen. That change, called the Suess effect after the scientist who first discovered it, is the smoking or glowing gun connecting fossil fuels to the changing atmospheric CO2 content. Or is it? No, not if there are other sources of ancient carbon than human power generation.
Wielicki writes:
“Early in my career, I was struck by the Suess Effect, a shift in atmospheric carbon isotopes that seemed to pin the rise in CO₂ squarely on fossil fuel combustion. The evidence was compelling: burning ancient coal and oil, devoid of radiocarbon (14C) and depleted in 13C, was diluting the atmosphere’s isotopic ratios. It didn’t make me fear catastrophic climate change, but it convinced me humans were reshaping the atmosphere. Now, I’m not so sure. Recent discoveries and lingering contradictions suggest the story isn’t as clear-cut as we’ve been told. … [What] if the foundation is shakier than we thought? What if nature is playing a larger role in rising CO₂ than we’ve accounted for?”
As Wielicki explains, over the past year two studies have been published that show the current carbon cycle models are inadequate. In October 2024 a study came out from the US Oak Ridge National Laboratory showing that the world’s plants absorb 31% more CO2 each year than was previously thought. This finding on its own is a pretty stunning revision to the “settled science” carbon cycle models. But then in June 2025 another paper appeared that Wielicki says “may be the biggest challenge to the narrative yet.”
“The new paper studied the CO2 being released from ancient rocks as they are weathered away by the world’s rivers. That CO2 has an isotopic fingerprint identical to fossil fuels: devoid of 14C and depleted in 13C. What’s more, there is far more of it being emitted than previously believed. In fact the new paper says the amount of ancient carbon coming from rivers is on the same scale as the net land sink (the amount absorbed minus the amount released each year). Right now models don’t account for it at all.”
What does it all mean? At the very least that the carbon cycle models and carbon budget calculations on which so much climate policy relies are wildly inaccurate. Nature is a major source of old carbon, not just humans and nature is absorbing far more than we have assumed up to now so they have both outputs and inputs very wrong. Putting these errors together, Wielicki notes:
“These findings don’t erase the human footprint on climate. Fossil fuel emissions are real, measurable, and significant. But they do expose cracks in our understanding. If plants absorb more CO₂, oceans outgas more than expected, or rivers add uncounted ancient carbon, our models may overestimate humanity’s share of the CO₂ rise.”
So the settled science once again might be in for a major revision. Or due for one the gatekeepers of orthodoxy won’t permit. Something else we will be watching with interest.
So you are walking down a dark alley wherein you discover a dead guy with an obvious gunshot wound, you check for a pulse then you pick up the pistol lying next to him. At that moment our heroic first responders leap in and charge you with murder. This of course is analogous to man made vs natural CO2. If I recall correctly, the scientific method DEPENDS on doubt about the veracity of any theory, the lack of curiosity amongst these alleged scientists is amazing.