Dr. Jennifer Marohasy challenges the mainstream climate narrative, suggesting a significant but overlooked source of atmospheric CO2: the oceans. Using the vivid metaphor of a fizzing soda can, she highlights the possibility that warming ocean surfaces release more CO2 than currently acknowledged by climate consensus, which primarily blames fossil fuel emissions.
Marohasy critiques the reliance on isotopic analysis (the ratio of carbon isotopes ¹³C and ¹²C) to attribute rising atmospheric CO2 levels solely to fossil fuels. She argues this evidence might overlook key oceanic biological processes, particularly calcification near the surface, which can produce CO2 with similar isotopic signatures to fossil fuels.
Together with Ivan Kennedy, she proposes the Thermal Acid Calcification (TAC) hypothesis, suggesting that biological processes like coral and phytoplankton calcification in sun-warmed ocean surfaces significantly contribute CO2 enriched in lighter isotopes (¹²C). This could disrupt conventional assumptions used by the IPCC and others to attribute CO2 increases solely to human activity.
Overall, Marohasy calls for reconsideration of ocean chemistry and biology in climate discussions, emphasizing natural processes potentially playing a larger role than current models recognize.
| Whose C02 is it Anyway? | |||
|---|---|---|---|
| Factor/Issue | Ocean Surface Calcification (Marohasy Hypothesis) | IPCC Position & Assumptions | Comparative Analysis & Implications |
| Source of post-LIA CO₂ increase | Significant portion (~90–100 ppm) due to enhanced ocean surface calcification as temperatures rose. | Majority (~100–120 ppm) attributed to fossil fuel emissions and land-use change since ~1850. | Marohasy hypothesis presents a competing natural source, challenging the attribution of most CO₂ rise to human activity. |
| Estimated atmospheric CO₂ increase since LIA | ~140 ppm total (from ~280 to ~420 ppm). Suggests calcification contributed 60–70% of this rise. | ~140 ppm total, with ~75–85% attributed to fossil fuel emissions. | Major attribution conflict. If calcification is responsible for a large share, IPCC attribution is significantly overstated. |
| Mechanism of CO₂ release | Warming increases biological calcification, which releases ¹²C-enriched CO₂ to the atmosphere. | Human combustion of fossil fuels releases CO₂ with a low ¹³C/¹²C ratio, altering atmospheric ¹³C. | Both mechanisms affect isotope ratios, but IPCC dismisses ocean calcification as a major contributor. |
| Impact on carbon isotope ratio (¹³C) | Surface calcification emits CO₂ depleted in ¹³C, similar to fossil fuels, lowering atmospheric ¹³C. | Declining ¹³C is used as strong evidence for fossil fuel attribution. | IPCC may be misattributing ¹³C changes, as ocean processes could produce similar isotopic signatures. |
| Timescale of effect | Long-term natural feedback accelerating since the end of the Little Ice Age (~150 years). | Primarily a modern industrial-era phenomenon (~since 1850). | Oceanic calcification spans both natural and anthropogenic eras, complicating the fossil fuel attribution timeline. |
| Response to temperature change | Calcification increases with warming due to biological and chemical sensitivity. | Warming is seen as a response to CO₂ increase, not a cause of CO₂ release. | Reverses causality: Marohasy sees temperature driving CO₂ (natural outgassing), not the other way around. |
| Policy implications | Suggests large part of CO₂ rise is natural and not easily controllable via emission reductions. | CO₂ rise is anthropogenic and controllable through emissions cuts (Net Zero policies). | Undermines the foundation for urgent mitigation if much of CO₂ increase is naturally sourced. |
From Walter Shepherd
Compiled with the help of ChatGPT
10th April 2025
This table is available as an easy to download and print off in PDF, click here.
The TAC hypothesis is building on the work of Ivan Kennedy and colleagues with important foundational modelling already published, click here.
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