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, rather than just humans, is a major source of old carbon, and moreover 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.
This could mean that natural CO2 may account for a higher percentage of emissions than previously believed?Yes,the climate alarmist house of cards is slowly beginning to collapse.Has been for awhile now.Love it!Hope it happens!
At least nine of 10 articles here are good and I recommend them on my own climate and energy blog. With over 1.1 million lifetime page views. This article is an embarrassment. Because I've recommended many good Wielicki articles in the past.
Nature has been absorbing CO2 for billions of years. In the past 150 years, atmospheric CO2 increased about 50%. What caused that is very simple. Humans added enough CO2 to double the atmospheric CO2 level. Nature absorbed about half of that added CO2. The result was a 50% rise of atmospheric CO2 since 1850. The recent increase of 50% (from around 280 ppm to over 420 ppm) is unprecedented in the last several hundred thousand years and is directly linked to human activities, primarily the burning of fossil fuels. This is so simple a 12 year old child could understand it. Yet there is a PhD who seems clueless.
... Measurements show a decrease in both {13}C and {14}C in atmospheric CO2, which is consistent with the addition of CO2 from fossil fuels, as fossil fuels are depleted in both isotopes due to their origin in ancient biological matter and their age. While different CO2 sources do have distinct isotopic signatures, the specific changes observed in atmospheric carbon isotope ratios point strongly to anthropogenic fossil fuel combustion as the driver of the recent CO2 increase. Conservatives sometimes embarrass themselves with the false arguments that CO2 is all natural or that CO2 does nothing! Liberals often embarrass themselves by claiming CO2 does everything! Climate science tells us man emitted a lot of CO2 to the atmosphere and it caused some amount of global warming.
https://honestclimatescience.blogspot.com/
Dear Richard Greene (nice surname for climate by the way). You seem to be reasoning from a point where humanity is to blame for something. In doing so, you're making several assumptions that are common for climate alarmists but wrong as well as some basic logic flaws.
First the logic flaws: a 12 year old child can understand that Thor is angry at us for not sacrificing enough sheep and that's why there's a thunderstorm. And that's also why the neighbour's farm was struck by lightning and not ours, because we're much more faithful... The fact that it's an easy to understand explanation that fits the preconceived world-view doesn't make it correct. In fact, this is a common tactic of professional scammers: tell a lie that sounds believable, knowing that you'll be gone before people have time to actually think it through OR in the case of any science that most people simply don't understand the details well enough to see the flaws. It is very important to recognize these biases in oneself, especially when looking at something that disagrees with your world view.
Next, the 'unprecedented' recent increase: you mentioned a geologically narrow timeframe in which you may be right (I don't know the exact data), but I am certain that more pronounced changes have occurred longer ago. At least one of the big glaciation events had both a sharp drop and a sharp rise in CO2, I'm sure there are more. You may be technically correct due to your addition of a limited time, but you imply more by adding 'unprecedented'.
Then, the 'man emitted a lot of CO2 to the atmosphere and it caused some amount of global warming'. This is actually a point of debate. There are several studies that show that adding CO2 to the atmosphere has no effect at all on the temperature on earth, for all kinds of reasons. I'll just list a few: cloud-coverage (resulting in a different albedo) of the planet matches very well with temperature changes (leaving no room for any additional greenhouse effect); the atmosphere is way past its saturation point for CO2 regarding greenhouse effects (meaning if there is a greenhouse effect from CO2, it's already maxed out); historically CO2 tends to follow temperature changes delayed by a few hundred years (which is actually what we're seeing now, we're now getting the additional CO2 from the medieval warm period).
The article states that the math that proves that humans did it all is at least flawed and needs to be critically reevaluated. Whether the result is that we're still responsible for the rise in CO2 or not or something in between is currently unknown.
And until we're CERTAIN that humanity is 1) causing the CO2 increase, 2) the CO2 increase is causing warming, 3) the warming is DEFINITELY going to be CATASTROPHIC, no policy should be made or enforced to actually limit the amount of CO2 produced (other than to prevent smog/pollution due to very old power plants or impure fuels such as brown coal)
I read your silly science and had a good laugh.
Atmospheric CO2 has to be natural or manmade.
If humans have added 1x CO2 to the atmosphere, and atmospheric CO2 increased by 1/2 x, then nature must be a CO2 absorber. And nature has been a CO2 observer for billions of years.
I have followed the subject of climate science for 28 years. My Climate Science and Energy blog has had over 1.17 million page views. I don't waste my time with the silly science, like there is no greenhouse effect, CO2 does nothing and CO2 is 100% natural. Those false claims are for science deniers like you. ...
Concerning cloud cover percentage: The decline of cloud cover percentage in the past 25 years is less than the likely margin of error in the measurements. That makes the data statistically insignificant. Nut if we want to trust the cloud data reduce cloudiness would cause warmer days and cooler nights. The actual pattern of climate change in the past 50 years is warmer days, but more warming at night (TMIN). The likely cause of warmer nights is CO2 emissions. ... Temperature does not lead manmade CO2 emissions. ... CO2 is not anywhere close to being saturated, nor will it ever be saturated. I wrote an article on the subject that would be way over your head. Perhaps someone else would be interested?
https://honestclimatescience.blogspot.com/2024/04/tthe-greenhouse-effect-co2-is-saturated.html
Your comment is a perfect example of why liberals call conservatives science deniers. The liberals predict global warming doom. But after 50 years of global warming, it's obvious that warmer winters are very pleasant. armer winters are a primary symptom of greenhouse warming. I believe CO2 emissions and global warming should be celebrated.
I would think a 6000 year coal seam fire would be indistinguishable from human 'emissions' and not insignificant.
https://www.youtube.com/watch?v=4WqIKlapg_M
This topic was discussed in depth on WUWT with a lot of replies back and forth:
https://wattsupwiththat.com/2025/06/25/under-reported-old-carbon-is-not-the-source-of-increases-in-atmospheric-co2/
The main point is that such natural releases are at work since there was water and land on this earth. There were of course natural variations, but based on the 13C/12C ratio in CO2 over the past 800,000 years in ice cores of -6.5 +/- 0.4‰ δ13C, with about 90 ppmv change over glacial - interglacial transitions, these were very modest. Only since about 1850, the δ13C ratio in the atmosphere and the ocean surface dropped enormously to currently -8.2‰ δ13C in the atmosphere, completely in ratio to human emissions.
It would be very remarkable that natural changes would respond to human emissions...
Wielicki made an error by assuming that the river discharge of CO2 is depleted of 13C, but that is mostly from carbonate rocks that are near zero ‰ δ13C. When that dissolved CO2 is released to the atmosphere, there is a shift in composition towards the lighter isotopes and that gives an average of -6.5‰ δ13C in the atmosphere, still higher than the -8.2‰ δ13C of the current CO2 in the atmosphere.
The only point of interest is that the increase of CO2 in the atmosphere increases the releases of river CO2 from ancient deposits, which can be interpreted as a positive feedback for the 14C drop and a negative feedback for the 13C drop in the atmosphere.