Thinking with Mold: Metabolizing the Planet in a Changing Climate

I’m a social anthropologist, not a biologist or mycologist. But like everyone else on planet earth, I live with those environmentally ubiquitous, filamentous fungi that are commonly referred to in English as mold. 

Aspergillus molds grow on the vegetables I store in my cupboard and the coffee grounds I throw onto my garden soil. Penicillium molds grows on the leftover dal I keep forgetting about in my fridge. Stachyboytrys molds grow under my feet, beneath the floorboards in my home and in the sealant around my bathroom.    

For most of my career, I have not paid these molds much anthropological attention. Over the past five years, however, as I have been researching how people live with, adapt to, and build solutions to weather patterns that are attributable to rising greenhouse-gas emissions, I have come to understand that mold is everywhere. Not as invisible spores in air, soil, and food or as visible mats of filaments—hyphae—but as objects of public interest amid changing planetary climates.

Across North America and Europe mold is having what we might call a cultural moment. A surge of aesthetic interest in mold is giving rise to novel techniques for time-lapse photography of decay—like those used in the 2022 short Wrought by Canadian filmmakers Joel Penner and Anna Sigrithur—and new methods for “co-creating” art with mold. like those pioneered by Danish-Japanese artist Silas Inoue. Haute cuisine and sustainable cookery, too, have a newfound interest in mold as a natural agent of fermentation inspired by traditions of Japanese food production, as captured by the best-selling cookbook Koji Alchemy by Jeremy Umansky and Rich Shih. Meanwhile, in theatre and television, mold has appeared as a dramatic agent of public health; it takes center stage in the 2024 off-Broadway hit-musical Lifeline (formerly The Mould that Changed the World), which charts the history of penicillin in twentieth-century medicine, and in the satirical HBO series The Regime (2024), in which the power of a European autocrat is constantly threatened by her fear of toxic fungi. 

As I have discovered while studying how people live with extreme heat and rainfall, mold is as ubiquitous in social life as it is in our environments. Mold talk, however, is rarely about fungal ecology. Rather, mold is frequently used as what linguists might call a signifier of something else: dampness or humidity, degradation or decay, spoilage or sourness, poverty or inequality, nature or the nonhuman. As we enter the second quarter of the 21st century, mold has also emerged as a visceral, cross-cultural signifier of planetary climate change.

In contrast to yeasts and mushrooms, mold has been relatively absent from writing and theorizing about life with plants and fungi across the social sciences and humanities (see, for example, the collection of essays gathered in this volume). As an academic, I’ve begun to find that strange, particularly given how much of our work and our source materials are going moldy in libraries. 

Take the Harvard Divinity School library, housed in the same building where the 2025 Thinking with Plants and Fungi conference took place. When I visited on a conference break, the librarians told me they were constantly battling mold. In the main storage spaces, every fifth shelf contains a humidity monitor that helps to keep in check the fungal-mediated biodeterioration of the books, manuscripts, and journals as well as the stacks that contain them. It’s a challenge, particularly as rising annual precipitation rates and average temperatures increase both humidity levels inside the building and the risk of leaks. 

And it is not just Harvard. A recent global survey of libraries found mold present in air samples, dust, and book surfaces from Portugal to Iraq, Egypt, and to Slovakia.¹ These molds endanger the archives where they grow as well as the health of librarians and patrons. 

These opportunistic library molds have proved good for entrepreneurs. Over the past 20 years, the problem of mold in libraries has provided a justification for the world’s technology companies to scan written materials. These digital archives are then used to train the large language models of the artificial intelligence that’s transforming our societies and economies, in the process massively increasing the consumption of energy and water, which data centers use for cooling. When I asked ChaptGPT-4o if that meant it was born from mold, the AI told me the link was poetic and that more accurately it was “born from the impulse to resist mold.”²

More than any other genus of filamentous fungi, human lives around the world are entangled with Aspergillus molds. Although their precise taxonomy and genetic relationships continue to be the subject of much debate, one internationally recognized nomenclature repository for fungi - Index Fungorum - lists over 250 species of Aspergillus that exhibit uniquely versatile and adaptive metabolic capacities. 

Aspergillus molds can turn any organic compound—from carbohydrates and proteins to plant matter, paper, and wood to hydrocarbons and thermoplastics—into energy. They can also absorb inorganic compounds, such as iron, copper, zinc, and manganese. As they do so, many produce secondary metabolites that are pathogenic to plants and humans but of critical value in medicine and industrial production processes. These metabolic traits link Aspergillus molds to a range of negative health conditions, from asthma to sick-building syndrome and, especially in immunocompromised individuals, the invasive lung disease Aspergillosis. They are also what makes Aspergillus molds particularly interesting to industry, where they are being used in the production of citric acid, biological metallic nanoparticles, and drug discovery. 

Aspergillus molds are environmentally ubiquitous worldwide. But it is their capacity to metabolize such an extraordinarily diverse range of substrates that allows them to appear across the very different worlds of business, industry, science, and public policy. For anthropologists, how we understand and represent the metabolic capacity of microbial life is both social and political, a reflection of cultural attitudes and interests.³

One framework for tracking these changes, developed by MIT anthropologist Heather Paxton and Oxford geographer Jamie Lorimer, helps to identify shifts and changes over the past two hundred years.⁴ On one hand, Aspergillus molds have been culturally constructed as potentially harmful, demanding interventions aimed at controlling, sterilizing, or eliminating them. This is what Paxton refers to as a “Pasteurian microbiopolitics” and what Lorimer calls “being antibiotic.” On the other hand, Aspergillus molds have been scientifically constructed as potentially beneficial, and essential components of complex ecosystems. This is what Paxton calls a post-Pasteurian and Lorimer calls “being probiotic.” As I explore in this essay, when Aspergillus molds circulate in our environments and societies today, these two paradigms are constantly held in tension.

A different framework appears in a Marxist tradition of writing about economy and society that explores how relationships between humans, plants, and fungi have been transformed under industrial capitalism. In the 19^th century, Karl Marx incorporated into his writings an idea of metabolism developed by his peer, the German scientist Justus von Liebig, who pioneered a chemical and biological understanding of nutrient cycles in the soil. In Marx’s canonical texts, a precapitalist relationship between humans and nature was presented as profoundly metabolic, with humans working upon, consuming, and returning the earth’s material resources to the soil. Under the conditions of industrial capitalism, however, as nutrients are extracted from the soil and transported to new sites rather than being returned, the cycle is broken. The Marxist scholar John Bellamy Foster calls this rupture a “metabolic rift.”⁵ For contemporary scholars, such metabolic thinking provides a powerful way of describing how systems of extraction, production, and consumption have accelerated the depletion of planetary resources.⁶ As we reflect on human relationships to fungi, this framework offers us a powerful reminder that the metabolic capacities of Aspergillus molds and the substrates they metabolize are deeply entwined in capitalist economies that are driving climate change.

The word Aspergillus provides us with a vital linguistic register for understanding the potency and politics of these metabolic processes in contemporary life. Aspergillus was discovered in 1729 by the Italian botanist Pier Antonio Micheli, who named its spores for their resemblance under the microscope to the aspergillum, a Latin word for the object used in the Catholic Church to sprinkle holy water.⁷ The etymological root (spargere, to sprinkle) spans Indo-European languages and provides us with powerful binaries: The words disperse and aspersion in French, Italian, Spanish, and English derive from it; it is used in a positive sense to mean the spreading of seeds or light and in a negative sense to mean the casting of blame or damage; and in South Asia, the same root gives us the Sanskrit and Hindi words prasarga and visarga, which are used to invoke the discharge of positive or negative substances, nectars or poisons. 

This duel register perfectly captures the ways in which Aspergillus molds appear across diverse social and cultural contexts today. Against the backdrop of climate change Aspergillus molds and their metabolic capabilities have distinct positive and negative possibilities. In some places, molds are undesirable, uncontrollable, and potentially harmful. In others they hold out the promise of a magical elixir capable of rejuvenating planetary fortunes. How they are represented depends on what is being metabolized, in what context, and in proximity to whom. To illustrate, let me provide two examples. Both begin with panic, since this is increasingly where much public debate about our entanglements with mold and climate change start.

During the second wave of COVID-19 in India, hospitals witnessed a spike in “black fungus.” Better known to doctors as mucormycosis, this is a fungal infection that affects the sinuses and lungs and is caused by a group of molds called Mucormycetes. In mid-2021, an unprecedented outbreak of mucormycosis occurred in India, with 70 percent of all  infections globally appearing there at the end of extreme tropical heat waves and amid torrential monsoons.⁸ Scientific explanations acknowledged the role of comorbidities like COVID and diabetes but also environmental conditions that meant masks, bandages, and bed linens kept in hot, humid indoor storage spaces were likely being contaminated with spores.⁹

The sudden rise in infections also saw an increase in alternative, popular nonscientific explanations about the mold’s origins. In May 2021, stories posted on Indian social-media networks claimed that black fungus was caused by moldy onions. These claims went viral, prompting public health officials to publish fact checks. India’s national and regional media denounced the information as fake and sought to provide clarifications,¹⁰ but the story gained traction.

In many respects, this mold panic reflected the online conspiracy theorizing and scientific distrust that was a prominent feature of the COVID-19 pandemic. But it had another dimension. In India, onions are a kitchen staple that are grown in rural hinterlands and transported to cities. Over the past decade, onion supplies have been highly volatile, making their cultivation a highly speculative gamble.¹¹ One of the principal causes is Aspergillus niger; widely recognised as a black rot that degrades the quality and marketability of onion bulbs after they have been harvested.

Like other Aspergillus species, A. niger has a distinct capacity for thermotolerance. It thrives in the climatic conditions attributed to climate change: higher than average temperatures and heavier than average rainfalls. These conditions are also increasingly understood as an environmental trigger that, at the cellular level, increases the mold’s tolerance or resistance to chemical fungicides. 

Amid rising prices, falling crop quality, and seasonal shortages of onions in Indian cities, concern over black fungus reflected broader anxieties over food security and climate change. Onions are valued in South Asian culinary traditions not simply for taste but also for a belief in their natural cooling properties, which are held to give them a role in regulating human bodily temperatures.¹² Yet beneath the public anxiety about black fungus lay another anxiety about the reliability and resilience of what keeps people cool and healthy in the context of a warming world.

As climate change and antimicrobial resistance in agricultural economies increase the concentration of potentially harmful Aspergillus species (in particular A. niger, A. fumigatus, and A. flavus) in food and food waste, they are also creating the rationale and a market for technical solutions. According to recent research partly funded by the IKEA Foundation, India loses approximately $14.33 billion worth of crops each year post-harvest, with less than 10 percent of agricultural produce passing through a refrigerated supply chain. The report projects a $19.2 billion opportunity in cold chain infrastructure, from packhouses to trucks, by 2030.¹³

Refrigerated cold chains for vegetables—we might also call them “mold chains”—are designed with the single purpose of suppressing microbial growth and curtailing degradation in order to maintain the quality and shelf life of perishable food.¹⁴ Innovations in cold chain storage, like those that harness solar power and digital technologies to manage temperature controls remotely and off the grid, seek to do this more affordably, more effectively, and more efficiently than ever before, attracting climate finance from governments and investment firms.

Bio panics about Aspergillus mold are not peculiar to South Asia. In the UK, at least one third of all residential building stock has a mold problem.¹⁵ Over the past 150 years, changes in interior decoration and building technologies have created new interior substrates in UK homes. The increased use of wallpaper, oil based paints, and drywall or gypsum plasterboard have all created new interior surfaces for molds to flourish. Meanwhile the increased use of mechanical heating and cooling systems and windows filled with insulating gas means many newly built homes have little air flow, which creates indoor atmospheres with high humidity. 

Public concern with Aspergillus mold in the UK has a long history. Thirty-five years ago in Glasgow, for example, a community theater group staged a play called Dampbusters, written by a local housing activist, Cathy McCormack. The play envisaged a domestic scene between penicillin and Aspergillus as they reunited in the sitting room after one of them had been in a cupboard.

Dampbusters was a powerful example of the emergence of specific mold genera into public consciousness. But over the past decade, anxiety about toxic mold has risen dramatically, driven in part by cuts in public funding for rent controlled affordable homes that have precipitated a national housing crisis.¹⁶ In 2020, a coroner announced that the death of a two-year-old Sudanese immigrant, Awaab Ishak, in low-rent social housing could be attributed to mold. His death led to a public outcry and major new housing legislation designed to protect tenants not just from opportunistic molds but from opportunistic landlords who minimize their costs and maximize their returns from property by willfully neglecting maintenance.

Across the UK, uncertainty over whether mold is toxic has created demand for reputable information and mold specialists. Facebook lists more than a hundred English-language support groups organizing around toxic mold. In British cities, mold removal experts often market their services via these groups, offering surveys and treatments. Mold anxieties have also created a new market for prepaid  home testing kits. As the advert for one £40 ($55) online DIY kit puts it, “Every home has some mold, but not every home has a mold problem.”

Such anxieties underpin media reaction in the UK to research about the impacts of climate change on Aspergillus, funded by the global charitable foundation Wellcome Trust. Earlier this year, a team of biologists and epidemiologists published a new study mapping Aspergillus mold onto scenarios envisioned by the UN’s International Panel on Climate Change.¹⁷ These scenarios represent the scientific consensus for what kinds of planetary-scale changes in temperature, rainfall, and land use we can anticipate by the end of the 21^st century based on varying degrees of radiative forcing, the process through which atmospheric greenhouse gas emissions trap heat.

The research projected the gradual spread of three Aspergillus species—A. fumigatus, A. niger and A. flavus—across Europe and North America in the next 15 years based on current levels of emissions. It concludes that the molds’ expanding geographic range would impact the spectrum of aspergillosis disease in plants, crops, and humans. In the UK, the research produced headlines and articles ranging in tone from the urgent to the apocalyptic. As the Financial Times reported, “A. Fumigatus could spread to an additional 77 per cent of territory by 2100 if the world continues to use fossil fuels heavily.” As the UK’s Daily Mirror put it, “ ‘[k]iller fungus’ plague . . . could cause millions of agonizing deaths.”¹⁸

What animates these panics around Aspergillus molds that are so ubiquitous in human life? One explanation might be that molds have broken loose. They are metabolizing the very infrastructures and technologies with which humans have managed fungal life for much of the 20^th century. Studies report that emerging strains of Aspergillus that are resistant to dominant azole-based fungicides are five times more likely to acquire resistance to new chemical treatments.¹⁹ They have, as the authors of the 2024 book Field Guide to the Patchy Anthropocene put it, “gone feral.”²⁰

Perhaps it is no surprise, then, that at the very same historical moment Aspergillus molds are evolving beyond our capacity to eradicate or control them, we find a surge of interest in the possibility of harnessing or capturing their capacities for human ends. Just as newspaper headlines amplified public anxiety about a new killer mold, the UK’s Office for Science released a new report on the country’s aspirations for engineering biology, which laid out the economic opportunities for modifying mold to produce vital materials without polluting the planet.²¹ Here, Aspergillus molds are the solution, a means of greening industrial processes.

In a key chapter, the report celebrates the potential to put molds like A. fumigatus to work in “microbial metal factories” where they can be made to extract, recycle, and recover critical minerals from industrial and electronic waste flows, from low-grade copper and iron ores to electric cabling and lithium-ion batteries. Gene editing and genetic-manipulation techniques are being used to speed up this metabolic process, growing molds that can more cleanly and efficiently produce metallic nanoparticles. For the UK government, this is a potential new engine of the biotech economy. Against the backdrop of feral molds, it is difficult not to see policymakers’ newfound enthusiasm for biologically re-engineering Aspergillus molds as part of a cultural project to re-establish or reassert control over fungal life.

What might it mean to think with mold in the face of public anxiety and private-sector ambition? At the very least, it means grappling with the ways that molds exist on a planet that continues to be transformed by human activity—modifying the biology and habitats of mold even as they modify us. But perhaps it also means acknowledging our metabolic entanglements. 

Just as thermotolerant Aspergillus molds find ecological opportunity in compromised books, deteriorating buildings, damp utility poles, vulnerable bodies, and a warming planet, so too do enterprising individuals and companies, optimizing new pathways to profit and gain. In some contexts, the byproducts of this metabolic process are undesirable, uncontrollable, and potentially harmful—but in others they are being reimagined, reengineered, and repackaged as the solutions to climate adaptation. How these dynamics unfold and with what effects will shape how we think about fungal life over the course of the 21^st century.   

¹ Islam El Jaddaoui, Hassan Ghazal, and Joan W. Bennett, “Mold in Paradise: A review of fungi found in libraries.” Journal of Fungi 9.11 (2023), 1061. [Return to Section]

² Conversation with ChatGPT, OpenAI, March 2025, https://chat.openai.com/chat. [Return to Section]

³ See, for example, Heather Paxson and Stefan Helmreich. “The perils and promises of microbial abundance: Novel natures and model ecosystems, from artisanal cheese to alien seas,” Social Studies of Science 44.2 (2014), 165–193. [Return to Section]

⁴ Heather Paxson “Post‐pasteurian cultures: The microbiopolitics of raw‐milk cheese in the United States,” Cultural Anthropology 23.1 (2008): 15-47; Jamie Lorimer, The Probiotic Planet: Using Life to Manage Life (University of Minnesota Press, 2020). [Return to Section]

⁵ John Bellamy Foster, Brett Clark, and Richard York, The Ecological Rift: Capitalism’s War on the Earth (New York University Press, 2010). [Return to Section]

⁶ See for example Kohei Saito, Marx in the Anthropocene: Towards the Idea of Degrowth Communism (Cambridge University Press, 2023) and Nancy Fraser, Cannibal Capitalism: How our System Is Devouring Democracy, Care, and the Planet—and What We Can Do about It (Verso Books, 2023). [Return to Section]

⁷ Hugo van den Bossche, Donald WR Mackenzie, and Geert Cauwenbergh, eds. Aspergillus and aspergillosis (Plenum Press, 1988). [Return to Section]

⁸ Gregoire Pasquier, “COVID-19-associated mucormycosis in India: Why such an outbreak?” Journal of Medical Mycology 33.3 (2023): 101393. [Return to Section]

⁹ Ibid. [Return to Section]

¹⁰ See, for example, Outlook Web Bureau, “Fact Check: Can You Catch Mucormycosis, or Black Fungus, from Onions?” Outlook India, updated January 16, 2024, https://www.outlookindia.com/national/india-news-fact-check-no-you-cant-catch-mucormycosis-from-onions-news-384541, and The Times of India, “Coronavirus Fact Check: Can you catch black fungus from your refrigerator or onions? Myth Busted!” The Times of India, May 27, 2021, https://timesofindia.indiatimes.com/life-style/health-fitness/health-news/coronavirus-fact-check-can-you-catch-black-fungus-from-your-refrigerator-or-onions-myth-busted/articleshow/82999700.cms. [Return to Section]

¹¹ See, for example, Tanya Matthan, “Speculative crops: Gambling on the onion in rural India,” Geoforum 130 (2022): 115-122. [Return to Section]

¹² See, for example, Chitrita Banerji’s Eating India: An Odyssey into the Food and Culture of the Land of Spices (Bloomsbury Publishing, 2010). [Return to Section]

¹³  Rahul Bagdia, Yamini Keche, Ankit Agrawal, Apurva Parakh, Akshay Gattu, Intellicap, and CLASP, Assessment of the Cold Chain Market in India (Efficiency for Access, 2023), https://www.clasp.ngo/wp-content/uploads/2023/06/Assessment-of-the-Cold-Chain-Market-in-India.pdf [Return to Section]

¹⁴ Jamie Cross, “Mold Chains: How is refrigeration mobilized against fungal life?” Limn 12 (2025),  https://limn.press/article/mold-chains/ [Return to Section]

¹⁵ UK Housing Ombudsman Service, Spotlight Report: Repairing Trust (Housing Ombudsman Service, May 2025). [Return to Section]

¹⁶ Megan Kane, “The violent uncanny: Exploring the material politics of austerity,” Political Geography 102 (2023): 102843. [Return to Section]

¹⁷ Norman van Rhijn, Christopher Uzzell, and Jennifer Shelton, “Climate change-drive geographical shifts in Aspergillus species habitat and the implications for plant and human health,” preprint, https://www.researchsquare.com/article/rs-6545782/v1 [Return to Section]

¹⁸ Michael Peel, “Killer fungi to spread as climate heats up,” Financial Times, May 3, 2025, https://www.mirror.co.uk/news/health/inside-killer-fungus-plague-could-35182311; Sarah Tulloch, “Inside ‘killer fungus’ plague that could cause millions of agonising deaths,” Daily Mirror Online, May 7, 2025, https://www.mirror.co.uk/news/health/inside-killer-fungus-plague-could-35182311. [Return to Section]

¹⁹ Michael J. Bottery, Norman van Rhijn, Harry Chown, Johanna L. Rhodes, Brandi N. Celia-Sanchez, Marin T. Brewer, Michelle Momany, Matthew C. Fisher, Christopher G. Knight, and Michael J. Bromley, “Elevated mutation rates in multi-azole resistant Aspergillus fumigatus drive rapid evolution of antifungal resistance” Nature Communications 15 (2024): 10654. [Return to Section]

²⁰ Anna Lowenhaupt Tsing, Jennifer Deger, Alder Keleman Saxena and Feifei Zhou, Field Guide to the Patchy Anthropocene: The New Nature (Stanford University Press, 2024). [Return to Section]

²¹ UK Government Office for Science, Engineering Biology Aspirations: Foresight Report (Government Office for Science, April, 2025), https://www.gov.uk/government/publications/engineering-biology-aspirations-report/engineering-biology-aspirations [Return to Section]

Cross, Jamie. "Thinking with Mold: Metabolizing the Planet in a Changing Climate" in Thinking with Plants and Fungi: Interdisciplinary Explorations of Ecology, Mind, and the More-than-Human World, edited by Rachael Petersen, Russell Powell, and Natalia Scott Schwein. Center for the Study of World Religions, Harvard Divinity School, 2026. https://doi.org/10.70423/0003.05