HEADLINE: “New Evidence Questions Humanity’s Role In The Carbon Cycle”, by Dr. Matthew Wielicki

“Climatologist raises doubts about man-made CO2 causing climate change.”

New Evidence Questions Humanity’s Role In The Carbon Cycle

Climatologist raises doubts about man-made CO2 causing climate change.

by Dr. Matthew Wielicki

June 23, 2025, 8:09 AM

in Energy, News and Opinion, Science

Reading Time: 4 mins read

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Questioning the Fundamental Basis of Climate Science and Policy

As an isotope geochemist, I’ve spent years studying the subtle signatures that reveal Earth’s hidden stories. Isotopes, variants of elements like carbon, act as chemical fingerprints, tracing the movement, age, and origin of materials through time. [emphasis, links added]

They don’t lie, and they don’t bend to narratives.

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 that 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.

At the heart of climate science lies a critical assumption: we fully understand the carbon cycle, the complex dance of carbon through air, oceans, plants, soils, and rocks.

This assumption underpins every climate model, policy, and trillion-dollar investment. But 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?

Let’s explore the cracks in this narrative and ask a critical question: Are we really responsible for the carbon in the atmosphere?

Cracks in the Foundation

The carbon cycle is Earth’s grand accounting system, tracking how carbon moves between vast reservoirs: the atmosphere (850 petagrams of carbon, PgC), oceans (38,000 PgC), soils, vegetation, and fossil fuels.

According to the IPCC’s Sixth Assessment Report (AR6, Working Group 1, Chapter 5), natural processes like photosynthesis, respiration, and ocean-atmosphere exchange shuffle hundreds of gigatons of carbon annually, orders of magnitude more than human activity, which adds roughly 9.5 PgC per year through fossil fuel combustion and land-use changes.

Figure 5.12 in the IPCC report illustrates this beautifully, with yellow arrows showing natural fluxes and pink arrows marking human contributions. The deep ocean alone holds 40 times more carbon than the atmosphere, and natural fluxes dwarf our emissions.

Figure 5.12 | Global carbon (CO2) budget (2010–2019). Yellow arrows represent annual carbon fluxes (in PgC yr-1) associated with the natural carbon cycle, estimated for the time before the industrial era, around 1750. Pink arrows represent anthropogenic fluxes averaged over the period 2010–2019. The rate of carbon accumulation in the atmosphere is equal to net land-use change emissions, including land management (called LULUCF in the main text), plus fossil fuel emissions, minus land and ocean net sinks. Source: https://www.ipcc.ch/report/ar6/wg1/figures/chapter-5/figure-5-12

This isn’t to say human emissions are trivial. Even a small imbalance can tip the scales, gradually increasing atmospheric CO2. But the sheer scale of natural processes raises a question: How precisely do we understand these fluxes?

If our models miss even a fraction of nature’s contributions, the entire carbon budget, our estimate of sources and sinks, could be off. And with it, our confidence in attributing the CO2 rise solely to human activity.

The Isotope Fingerprint… and Its Smudge

The Suess Effect has long been climate science’s ace in the hole.

As fossil fuels burn, they release CO2 with no ¹⁴C (due to radioactive decay over millions of years) and less ¹³C than atmospheric CO2.

This dilutes the atmosphere’s isotopic ratios, a pattern observed since the Industrial Revolution. The IPCC cites this as definitive evidence that fossil fuels drive the CO2 increase, and I once agreed. The isotopic math seemed airtight.

But here’s the wrinkle: other natural sources can mimic this signature. Permafrost thawing in the Arctic releases ancient organic carbon, low in ¹⁴C and ¹³C. Petrogenic carbon from weathered sedimentary rocks does the same.

Deep ocean CO2, upwelled from centuries-old waters, carries a similar isotopic profile. These sources aren’t new, but their contributions are poorly quantified. If they’re larger than assumed, they could blur the line between “human” and “natural” CO2.

The Suess Effect remains strong evidence, but it’s not the unassailable fingerprint we once thought. Could we be overconfident in our attribution? (I discussed this in more detail in my article on the Suess Effect.)

Nature’s Lung Capacity… Bigger Than We Thought

Recent research deepens these doubts. A 2024 study in Nature Geoscienceused carbonyl sulfide (COS), a chemical absorbed by plants, to estimate global photosynthesis. (You can read more about that in my critique here.)

The result? Terrestrial ecosystems are soaking up 31% more CO2 than previously modeled. This suggests land plants are a more powerful carbon sink than we realized, which could shrink the net human contribution to atmospheric CO2.

If our models underestimated this sink, what else have we missed?

Source: https://scitechdaily.com/scientists-were-wrong-plants-absorb-31-more-co2-than-previously-thought/

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