The goal of climate restoration is important, and LOF deserves investigation as a research direction. But several claims in this piece don't hold up against the data, and overstating the science risks undermining the credibility of the very cause we are advancing. Let's walk through this carefully, because the corrections actually make the story more interesting, not less.

To verify the claims in this piece, I pulled the primary datasets directly: monthly CO2 concentrations from NOAA's Mauna Loa observatory (the Scripps/NOAA merged record), and monthly and annual temperature anomalies from NASA GISTEMP v4. I computed annual growth rates, baseline comparisons, and statistical measures from the raw data. The numbers below come from that analysis, not from secondary summaries.

1. CO2 never "disappeared." It just accumulated slower.

The Mauna Loa record shows CO2 rising every single year through the Pinatubo period:

• 1990: ~354.5 ppm

• 1991: ~355.7 ppm (+1.25)

• 1992: ~356.5 ppm (+0.84)

• 1993: ~357.2 ppm (+0.67)

What happened is the growth rate dropped from ~1.25 ppm/yr to ~0.84 and then ~0.67 ppm/yr, before recovering to ~1.74 ppm/yr by 1994. This is a reduced rate of accumulation, not a removal event. Saying 18 Gt of CO2 "disappeared" implies the atmosphere lost CO2. It didn't. It gained less than expected.

The ~18 Gt figure itself is defensible. It depends on what baseline growth rate you assume, and against a baseline of ~1.77 ppm/yr the cumulative deficit over 1991–93 comes out to roughly 2.5 ppm (~20 Gt CO2). But calling a growth rate slowdown a "disappearance" is a fundamentally misleading frame. Nothing was removed. The bathtub kept filling, just slower.

2. The "permanence" claim conflates two different things.

The CO2 growth rate returned to its prior trend by 1994–95. The "gap" persists only relative to a hypothetical no-Pinatubo world, not because carbon was permanently sequestered somewhere. It's like slowing down on a highway for two miles: you're permanently behind where you "would have been," but you didn't go backwards. Frölicher et al. (2011, 2013) modeled this explicitly and showed the ocean thermal signal gradually reverses on decadal timescales as temperatures recover.

3. Land photosynthesis is the leading explanation, not a failed one.

This is where the piece makes its most consequential error. You cite narrower tree rings to dismiss terrestrial uptake. But that evidence is only for high-latitude boreal forests where cooling shortened the growing season (Briffa et al. 1998, Nature).

The fuller picture is different. Gu et al. (2003, Science) and Mercado et al. (2009, Nature) demonstrated the "diffuse radiation fertilization effect": Pinatubo's aerosol veil scattered sunlight, increasing the diffuse fraction. Diffuse light penetrates forest canopies more uniformly, reaching understory leaves that direct sunlight misses. Mercado estimated this enhanced the global land carbon sink by 0.7–1.1 Gt C during 1992–93. Combined with reduced soil respiration from cooling, terrestrial processes account for an estimated 60–80% of the observed anomaly in current IPCC synthesis literature.

In other words, the explanation you dismiss first is actually the one the field considers strongest.

4. The anomaly is real but not as exceptional as presented.

The 1992 growth rate of 0.84 ppm/yr sits about 1.1 standard deviations below the long-term mean (1.61 ± 0.67 ppm/yr, 1960–2020). That's below normal, but not statistically remarkable in any single year. What makes the Pinatubo signal credible is three consecutive below-baseline years. But even that needs to be weighed against the fact that ENSO variability routinely produces comparable swings. The 1998 El Niño drove the growth rate to 2.96 ppm/yr, a far larger departure from the mean than anything Pinatubo produced.

5. The "3 of 9 eruptions" selectivity argument can't be verified.

For eruptions before 1958 (pre-Keeling curve), we have only ice core CO2 data with temporal resolution of years to decades. That is far too coarse to detect a 1–2 year growth rate anomaly of ~0.5 ppm. Of the three eruptions during the instrumental record (Agung 1963, El Chichón 1982, Pinatubo 1991), only Pinatubo has a clear, unambiguous CO2 signal. El Chichón's signal is hopelessly entangled with the massive 1982–83 El Niño.

The selectivity pattern you describe, the linchpin of the LOF argument, rests on data that doesn't have the resolution to support it.

6. LOF as a hypothesis: promising direction, but presented with false confidence.

The core LOF claim rests heavily on one experiment: EIFEX (Smetacek et al. 2012, Nature), which achieved ~50% carbon export inside a closed Southern Ocean eddy. That result is real and genuinely interesting. But it's the sole experiment out of 13 major OIF experiments to achieve significant deep export. LOHAFEX (2009), specifically designed to replicate EIFEX, failed. Copepod grazing recycled the carbon before it could sink.

There's also a mechanistic problem the piece glosses over. Recent work (Science Advances, 2025) shows that anticyclonic (downwelling) eddies enhance CO2 uptake through physical pumping but actually suppress biological production by pushing nutrients deeper. Cyclonic (upwelling) eddies are the ones that stimulate phytoplankton growth. The eddies that grow the biology and the eddies that sink carbon aren't the same eddies.

The iron to nitrogen-fixing bacteria to solving nutrient limitation chain has a legitimate scientific basis (iron does limit nitrogenase), but it's a multi-step pathway with uncertain efficiency at each step, and phosphorus co-limitation caps the benefits in many regions.

7. Hunga Tonga is worth mentioning.

The January 2022 Hunga Tonga eruption offers an interesting comparison, though it doesn't cleanly test LOF. It injected only ~0.4 Mt SO2 (2–3% of Pinatubo) but an unprecedented ~146 Tg of water vapor into the stratosphere (Millán et al. 2022, Science). The result was net warming, not cooling, making it the first well-documented volcanic warming event. No CO2 drawdown was observed; the growth rate actually accelerated to 3.0 ppm/yr in 2023 and 3.4 in 2024 (driven primarily by El Niño). Both LOF and conventional frameworks predict no drawdown here (for different reasons), so it's not a discriminating test. But it reinforces that the relationship between eruptions and carbon is far more complex than the piece suggests.

8. What I think the honest version of this story is.

LOF is a legitimate research hypothesis that deserves the kind of investigation NASEM recommended in 2022 ($290–440M over 5–10 years). The EIFEX result is genuinely intriguing. The question of whether targeted iron fertilization near specific eddy structures could enhance carbon export is scientifically interesting and worth testing.

But the Pinatubo CO2 anomaly is largely explained by well-understood terrestrial mechanisms. It wasn't permanent sequestration. It was a temporary growth rate slowdown. And the selectivity argument can't be supported by available data. Presenting LOF as the "only hypothesis" that explains everything, when no peer-reviewed paper on it has been published and it rests on a single unreplicated experiment, risks the credibility of ocean-based CDR research more broadly.

The strongest version of the LOF argument doesn't need to overstate what happened after Pinatubo. It can stand on its own merits: EIFEX showed something genuinely promising, eddy dynamics are underexplored in carbon export, and a well-designed field trial could resolve the key uncertainties for under $50M. That's a compelling pitch. It doesn't need the Pinatubo mystery framing, and the framing, as constructed here, doesn't survive scrutiny.