The argument rests on a subtle but important distinction that applied mycology has long recognized yet rarely built into risk assessments. Every mycotoxigenic fungus has two overlapping but distinct ecological ranges: its growth window, the full set of temperature and water activity conditions under which it can colonize a substrate, and its toxin-production window, the narrower range in which the biosynthetic machinery for a given toxin is actually switched on. In nearly every species studied, the toxin-permitting range sits inside the growth range like a kernel inside a shell. Most models have treated these boundaries as fixed species properties, measured once on synthetic laboratory media such as potato dextrose agar and applied as constants ever since. Medina argues that this treatment is doubly flawed: fungi experience the food matrix itself as part of their environment, and boundary values measured on agar can differ considerably from those on the actual grain, nut or fruit at risk.

The factor that forced a reconsideration of these fixed windows is carbon dioxide. When elevated CO2 is added to the interaction between temperature and water availability in experimental systems, it does not simply increase toxin output under already favorable conditions. Instead, it widens the range of conditions under which toxin is produced at all, drawing the toxin-production window closer to the growth window. In studies of Aspergillus flavus on maize, interacting elevated CO2 with drought stress and increased temperature raised the expression of aflatoxin biosynthetic genes aflD and aflR and boosted aflatoxin B1 production, in some cases several-fold, under conditions that previously supported growth only. A parallel pattern, in which fungal growth changes little while toxin production expands, has been documented in pistachio-associated A. flavus and grape-associated A. carbonarius, although the degree and direction of the shift vary by species, strain and substrate.

There is also evidence that these windows are not merely plastic but can shift with repeated exposure. Strains of Fusarium langsethiae, F. poae and F. sporotrichioides sub-cultured for ten generations at 1000 parts per million of CO2 altered their subsequent growth and toxin-production responses relative to non-acclimatized strains, suggesting that successive generations can acclimatize to a changing atmosphere. Medina stresses that the direct CO2 effect has so far been demonstrated most convincingly in Aspergillus systems, and that confirming it across the wider fungal community remains a research priority. Still, the emerging picture is that climate change, acting through the interaction of temperature, water activity and CO2, does not merely make existing conditions more frequent. It modifies the ecological space available to toxigenic fungi, and often widens it.

The second half of the argument concerns timescale. Research on climate change and mycotoxins since the early 2000s has focused on combined rather than single factors, because studies varying one variable at a time consistently mis-estimated fungal behavior compared with combined-factor data. What has changed is the frequency with which these factors now cluster within a single cropping season rather than being spread across successive years. A season that once brought a single anomalous event, an early heat spike, a mid-season drought, a late intense rainfall, can now deliver several in sequence in the same field. Meanwhile, crop pests and pathogens have been shifting polewards at a mean rate of 2.7 kilometers per year since 1960, and temperature-dependent infection risk for fungal crop pathogens is projected to rise fastest at higher, increasingly productive latitudes. A framework built around isolated, spaced-out anomalies simply cannot describe a regime in which extremes compound within one crop cycle.

At the community level, this has a counterintuitive consequence. If growth and toxin windows widen and shift for multiple species at once, the previously separate temporal and spatial niches occupied by Fusarium, Aspergillus, Penicillium and Alternaria species within a crop cycle begin to overlap. Species that once took turns now compete for the same favorable conditions, and the outcomes are strain- and species-specific rather than predictable from single-factor data. Wider ecological windows, in other words, do not simply mean more toxin from one fungus. They may mean a larger, more crowded set of species with a genuine opportunity to contribute toxin to the same commodity at the same time. Medina proposes that the degree of overlap between the growth window and the toxin window could serve as a practical ecological metric for anticipating mycotoxin risk under climate change, one that can be estimated for a given species and matrix rather than assumed constant.

If the mechanism is general, its fingerprints should be visible in field surveys that were never designed to test it, and the evidence assembled in the Perspective is strikingly consistent with that prediction. Household maize in Kenya has been found to carry 22 different mycotoxins spanning both Aspergillus and Fusarium products, alongside 31 metabolites of A. flavus, with sharp regional differences between aflatoxin- and fumonisin-dominant areas. Brazilian cocoa has been reported carrying up to 15 mycotoxins from three fungal genera simultaneously. An 11-year survey of northern Italian maize found more than 85 percent of samples contaminated with two or more mycotoxins from Fusarium and Aspergillus jointly, and a seven-year survey across 23 European countries documented co-occurrence rates of 52 to 74 percent between trichothecenes and other Fusarium-derived emerging toxins. A ten-year global screen of 74,821 animal feed samples from 100 countries found that 64 percent of samples tested for three or more toxins contained at least two.

Multi-species coexistence is also visible within single crops, and species substitutions track the changing climate. In maize, hotter, drier conditions favor a shift from Fusarium verticillioides towards Aspergillus flavus dominance, and one modeling study projects a 92 percent increase in aflatoxin B1 risk in European maize under a two-degree warming scenario. PCR surveys of Spanish vineyards have found A. flavus on 67 percent of organically grown berries, A. niger on 44 percent and A. carbonarius on 14 percent, three toxigenic species routinely sharing the same fruit. On cereals, F. graminearum has displaced F. culmorum as the head-blight pathogen of Danish wheat, while Fusarium head blight has intensified under warming in southern England and central China, the latter accompanied by a shift toward a more toxigenic chemotype. The pattern even persists through processing: a UK survey of plant-based meat alternatives found emerging Fusarium toxins in up to 98.9 percent of samples and Alternaria toxins in up to 90.4 percent, while 78 percent of wheat flour samples from Shandong, China, carried deoxynivalenol together with two Alternaria toxins.

Medina is careful to flag the central confounder. Improved analytical capability, particularly broader liquid chromatography tandem mass spectrometry panels, undoubtedly accounts for a substantial share of the co-occurrence now being recorded, and multi-mycotoxin contamination is unlikely to be an entirely new phenomenon. But the same trend appears across independent surveys differing in continent, commodity and study design, which is compatible with a genuine biological contribution layered on top of better detection. Climate change should be viewed as a major interacting driver rather than the sole determinant, since agronomic practices, cultivar choice, trade patterns, storage conditions and sampling strategies all shape what is recorded. The proposed framework is offered explicitly as a plausible hypothesis rather than an established transition.

The practical implications are considerable, because the infrastructure of mycotoxin management remains anchored in a world of single toxins and single species. Predictive models that treat temperature, water activity and CO2 as separate, additive factors will systematically underestimate risk, since it is their interaction that widens the toxin window. Regulatory limits calibrated around single-compound thresholds do not address the toxicological consequences of co-occurring mycotoxins. Medina calls for surveillance to move to routine multi-mycotoxin analysis and near-real-time monitoring, noting that low-cost CO2 sensing has recently been proposed as an early warning signal because fungal CO2 output rises before toxin becomes detectable. Mitigation strategies validated under current conditions need re-testing under interacting future scenarios, and regulators from EFSA to Codex Alimentarius should treat multi-mycotoxin contamination not as an anomaly but as the baseline against which exceptionality is judged. Because the same crops, climate drivers and contaminated commodities flow through livestock and the wider environment, the author frames this as a One Health problem, shared by human, animal and environmental health sectors. The Perspective leaves readers with a memorable reframing: the black swan was never disappearing, it was multiplying, and the flock, not the single bird, is now the more accurate description of the risk.

Subject of Research: Climate change effects on fungal ecology and the risk of multi-mycotoxin contamination of crops and food

Article Title: Beyond the black swan: climate change and the evolving risk of multi-mycotoxin contamination

Article References: Medina, A. (2026). Beyond the black swan: climate change and the evolving risk of multi-mycotoxin contamination. Frontiers in Fungal Biology, 7, Article 1981215. https://doi.org/10.3389/ffunb.2026.1981215

Image Credits: AI Generated

DOI: 10.3389/ffunb.2026.1981215

Keywords: mycotoxins, climate change, fungal ecology, food safety, Aspergillus flavus, aflatoxin, Fusarium, CO2, ecological niche, surveillance, One Health, food contamination