Fish boomed when CO2 was five times higher and Earth was 5–8°C warmer
A new study shows that ocean life thrived with extremely high CO2 and very warm water, says Jo Nova. This runs totally counter to the catastrophe the IPCC is marketing.
Image created with AI
Jo Nova
Date: 2 November 2026
The hottest time since the dinosaurs died out has been held up as the posterchild of a carbon disaster, but it turns out that despite CO2 reaching a shocking 2,000 ppm or more plus temperatures being high, fish life boomed. All the panic about carbon dioxide ruining the ocean and acidification killing off the fish isn’t borne out by the data.
That doesn’t mean every fish species was happy about this rather wild kind of climate change, but it wasn’t the catastrophe we’ve been sold.
The PETM (Paleocene-Eocene Thermal Maximum) has been the choice pick of ancient disasters to warn us of the dangers of carbon dioxide. It occurred 56 million years ago, when volcanoes are estimated to have unleashed between 3,000 and 10,000 billion tons of carbon into the atmosphere. Global warming rose by 5–8°C and tropical fish swam near the poles. The warming lasted about 100,000 years. Just a blip, really, but long enough to wipe out plenty of fish if it was dangerous.
Currently humans are putting out about 40 billion tons of CO2 each year. So the volcanoes unleashed three hundred to nine hundred times as much carbon.*
Make no mistake, these researchers were tracking layers of fish teeth and scales that pile up on the ocean floor. They also looked at barium sulphate, which tells us how much carbon was being “exported” from the surface to the bottom of the ocean from all kinds of life, like phytoplankton. The message is that the entire marine food-production system may have become more productive. This runs totally counter to the catastrophe the IPCC is marketing.
This study took samples from six different sites spread across the world. Scientists had assumed that in a warmer world the ocean would stratify more — and separate into layers determined by density. That would suppress productivity because it would stop the mixing of heat, carbon and oxygen with nutrients upwelling from the deep. Now it appears that in a warmer world enough nutrients might be coming from above, from weathering off the land, to compensate for any lost from below. Did the gloomy predictions missed a potentially powerful counteracting effect?
Fascinatingly, as blockbuster as this paper by Zhou et al seems to be, this exact effect was reported in 2020 by Britten and Sibert. And that paper evidently disappeared like a stone, despite being presented at an AGU Conference. So many experts have known for years that carbon and warmer temperatures seem to be good for marine life, yet they didn’t feel they could speak up, and the media mentioned the results once in a dark corner somewhere and no one got excited. So Zhou et al have presumably repeated and expanded on the earlier work, and now that we are more confident of it, it will …also disappear like a stone.
Perhaps we can change that?
The chlorophyll concentration data are from the E.U. Copernicus Marine Service Information. Dark-blue squares and light-blue squares denote the sites of IAR from this study and previous studies, respectively. Brown circles and yellow circles denote the sites of BAR-derived Pnew from this study and previous studies, respectively. Due to a lack of barite records from Sites U1403 and U1514, the nearest Sites 549 and 738 are selected for data comparison. Small symbols indicate paleo-locations of the Paleocene-Eocene Thermal Maximum (PETM) sites at 56 Ma, with their corresponding modern locations shown as large symbols. Nature
We can see how stark the peaks are. Ichthyolith is a fancy word for tiny fossilized fish bones and scales, so the peaks show booms in fish life in the oceans at six different sites. The IAR means the Ichthyolith Accumulation Rate, and it reached levels that were five to 11 times higher than the background values.
So that would be something like 1,000% more fish — (loosely) in a couple of spots. We don’t know for sure because fish may have had more or less teeth, or grown and lost them faster. But it’s a lot of fish teeth. I am still amazed a fish tooth can survive 50 million years at the bottom of the ocean.
Of course, a bonanza of fish doesn’t necessarily mean some species weren’t wiped out. But it does mean we’ve been sold a panic attack by experts that really had no idea. And even when the experts figured it out, the truth takes years to fight its way to the surface.
It doesn’t have to be like this…
Dark-blue squares denote IAR data from this study. Light-blue squares denote recalculated IAR using the ichthyolith data from ref. and the updated dry bulk density and age model from this study. Error bars represent ±1 standard error (SE). Green circles denote bulk carbonate δ13C data compiled from published records. In all panels, the blue shading indicates the main carbon isotope excursion (CIE) interval (0-50 kyr), and the lighter shading indicates the recovery interval (50-250 kyr). Nature
These are tiny fish teeth, scales and other bits of fishy detritus. Microscopic….
Ichthyoliths from the upper Viséan of Czerna, Poland Michał Ginter and Michał Złotnik
As ancient oceans warmed, carbon export and fish productivity surged
— David Appell in Phys Org
A new paper looks at changes in fish biomass during a past episode of global warming and finds that sustained warming can stimulate open-ocean biomass growth as well as carry carbon taken up by marine plants and algae into the deeper ocean. But it takes a long while to happen. The study is published in the journal Nature Communications.
They combined measurements of the accumulations of fossil fish teeth and dermal denticles, together called ichthyolites—the second in the pair being tiny, flat V-shaped scales that are more like teeth than fish scales, found only in cartilaginous fish like sharks and rays—from six core sites in ocean sediment.
Ichthyolites are deposited on the ocean floor through natural shedding or excretion of indigestible parts by predators. The ichthyolite accumulation rate (IAR) served as the scientists’ proxy of pelagic fish productivity for the PETM.
The group also examined marine barite records from the same or nearby locations. The mineral barite (BaSO₄) in an ocean water column is produced, directly and indirectly, in association with decaying marine organic matter. Its distribution in both the water column and, for these purposes, ocean floor sediments corresponds closely to the organic carbon falling anywhere in the water column from the surface to the deep ocean.
The fish boomed at the same time as the carbon was ‘exported’ from the surface to the sea floor:
Carbon export fueled the increase
The group incorporated the cGENIE Earth-system biogeochemical model to determine the interaction of carbon, nutrients and more across the ocean, atmosphere, sediments and terrestrial systems. Doing so revealed that the widespread increase in pelagic fish productivity closely tracked the rate at which organic carbon was transported to the deep ocean, in the trends and in the spatial patterns across the seafloor. This suggests, they conclude, “the increase was fueled by enhanced carbon export from the surface ocean.”
Thus, under elevated carbon levels in the ocean, the effects of an enhanced nutrient supply seemed to outweigh the effects of ocean stratification—the separation of ocean waters into horizontal layers determined by density—which suppresses productivity because it obstructs mixing of heat, carbon, oxygen and other nutrients.
REFERENCE
Britten, G.L., Sibert, E.C. Enhanced fish production during a period of extreme global warmth. Nat Commun 11, 5636 (2020). https://doi.org/10.1038/s41467-020-19462-w
DeFranco, E. (2021), Ancient fish thrived during a period of rapid global warming, Eos, 102, https://doi.org/10.1029/2021EO210672. Published on 14 December 2021.
Zhou, X., Zhang, R., Tsang, MY. et al. (2026) Coupled increases in pelagic fish productivity and export productivity during the Paleocene-Eocene Thermal Maximum. Nat Commun 17, 10030 | https://doi.org/10.1038/s41467-026-77863-9
*Human emissions today are measured as CO2, but the ancient release was measured as carbon. One unit of carbon is a part of 3.67 units of CO2. Hence the math… human emissions of carbon are about 11 billion tons pa.
This article was published first on joannenova.com.au on 31 October 2026.
Jo Nova
Jo Nova is science presenter, writer, speaker & former TV host; author of The Skeptic’s Handbook.
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