The Hidden Biological Bomb: Could Thawing Ice Release Ancient Microbial Danger?

Introduction

Microbes form the foundation of all ecosystems, drive global biogeochemical cycles, and regulate greenhouse gas fluxes, yet they are under-recognized and have remain largely absent from climate policy and scientific assessments. Indeed, while Earth system models account for permafrost carbon stores, they typically omit detailed representations of microbial activity, the climate system’s “unseen elephant in the room”. Understanding microbial processes is, therefore, essential for predicting and mitigating the impacts of anthropogenic climate change. Microorganisms, bacteria, archaea, microbial eukaryotes, fungi, viruses, and phytoplankton govern key processes in carbon and nutrient cycling, soil fertility, plant productivity, marine primary production, and atmospheric chemistry [1]. In marine environments, phytoplankton perform nearly half of global photosynthetic carbon fixation and oxygen generation, while marine bacteria and archaea, remineralize organic matter, influence carbon sequestration, and modulate methane and nitrogen cycles. Climate-driven changes in ocean temperature, acidification, stratification, nutrient availability, and circulation alter microbial community structure, with cascading impacts on productivity, food webs, and carbon burial. Similarly, in terrestrial ecosystems, soil microbes regulate decomposition, organic matter storage, methane emissions, and nitrogen cycling.

Scientific studies and data available show that climate change affects microbial community composition, growth efficiency, evolutionary adaptation, substrate use, and metabolic pathways. Rapid warming, acidification, eutrophication, and pollution reshape microbial interactions with plants, corals, and animals, influencing ecosystem resilience. Shifts toward harmful cyanobacterial blooms, pathogen proliferation, coral microbiome disruption, and altered plant-soil feedbacks exemplify these consequences. Moreover, climate change impacts microbial processes in agriculture, increasing methane emissions from rice paddies and ruminants, enhancing nitrous oxide release, reducing soil microbial diversity, and threatening global food security [1].

This article investigates the growing scientific concern that accelerating Arctic warming may revive long-dormant microbes, bacteria and viruses that have been preserved in frozen permafrost for thousands of years. Scientists argue that although much public attention is focused on greenhouse gas emissions and sea-level rise, the microbial risks associated with thawing permafrost remain insufficiently studied yet potentially consequential. This review article evaluates recent empirical evidence that appears to corroborate the hypothesis that, in the near future, the substantial thawing of ice-encased contemporary and archaic microorganisms, along with their genetic material and genomic structures, may precipitate localized outbreaks and potentially, global pandemics.

The Thawing Earth

The IPCC’s Sixth Assessment Report noted that each of the last four decades has been successively warmer than any decade that preceded it since 1850. The report noted that global surface temperature was 1.09°C higher in 2011-2020 than in 1850–1900. The increase in land’s surface temperature is relatively higher than over the ocean (1.59°C increase in land to 0.88°C increase in the ocean). This increase in the earth’s global temperature is mostly due to the observed increases in well-mixed greenhouse gas (GHG) concentrations since around 1750 which is unequivocally caused by human activities. Since 2011 (measurements reported in the IPCC’s Fifth Assessment Report), concentrations have continued to increase in the atmosphere, reaching annual averages of 410 ppm for carbon dioxide (CO₂), 1866 ppb for methane (CH₄), and 332 ppb for nitrous oxide (N₂O) in 2019 [2].

One of the effects of this human-induced global warming is the thawing of the earth’s cryosphere- the icy part of our planet- and the melting of the otherwise all-year-round frozen planet’s glaciers and ice sheets. This is evident from the increased frequency of extreme climactic warnings all over the globe. A trailside sign at the Sperry Glacier on the north slopes of Gunsight Mountain west of the Continental Divide in Glacier National Park in the U.S. state of Montana, alarmingly notes that the glacier has shrunk from more than 800 acres in 1901 (320 hectares) to less than 250 acres (100 hectares). The famed snows of Kilimanjaro have melted more than 80 percent since 1912. Glaciers in the Garhwal Himalaya in India are retreating so fast that researchers believe that most central and eastern Himalayan glaciers could virtually disappear by 2035 [3]. A study in 2018 reported that the winter ice sheet in the Bering Sea bordering Alaska was at its lowest levels in over 5,000 years [4]. At the end of July 2020, a study reported that 40% of the 4,000-year-old Milne Ice Shelf, Canada’s last fully intact ice shelf, calved into the sea and the St Patrick’s Bay ice caps completely disappeared [5].

To put this in context, the rate of ice sheet retreat has increased by nearly 60% since the 1990s. That’s a 28 trillion-ton net loss of ice between 1994 and 2017. Antarctica’s epic ice sheet, the world’s largest, and the world’s mountain glaciers have suffered half of this loss [6]. A new study, published in the journal Nature Climate Change, supports predictions that the Arctic could be free of sea ice by 2035 [7]. One of the world’s biggest carbon sinks, the Siberian tundra is now releasing greenhouse gases like methane that were long trapped below the frost. Similarly, thawing permafrost has caused the ground to subside more than 15 feet (4.6 meters) in parts of Alaska. Some scientists have predicted that by the century’s end, 40% of permafrost regions will have disappeared, releasing the deadly methane gas into the atmosphere [8].

Global warming has a triple effect on the cryosphere. Firstly, global warming is causing soils in the polar regions that have been frozen for as much as 40,000 years to thaw. Secondly, as they thaw, carbon trapped within the soils is released into the atmosphere as carbon dioxide and methane. These gases, released to the atmosphere, cause more warming, which then thaws more the frozen soil. Lastly, when solar radiation hits snow and ice, the icy white surface reflected back approximately 90% of it [9]. However, as global warming causes more snow and ice to melt each summer, the ocean and land that were underneath the ice are exposed at the Earth’s surface. Darker in colour, the ocean and land absorb more incoming solar radiation, and this causes more global warming. In this way, melting ice causes more warming and so more ice melts. This is known as feedback. The result of this triple warming effects is that the Northern Siberia and the Arctic are now warming three times faster than the rest of the world [5].

The thawing and melting of the cryosphere is supported by data reported in the IPCC’s Sixth Assessment Report, which noted that global warming has resulted in the global mean sea level rise by 0.20m between 1901 and 2018. It is important to note that while the average rate of sea level rise was 1.3mm between 1901 and 1971, it increased to 1.9mm between 1971 and 2006, and further increased to 3.7mm between 2006 and 2018 [10].

Global warming, is also affecting the permafrost, which currently holds about 1,600 billion tonnes of carbon, exceeding twice the amount in the present atmosphere [11]. As the Arctic experiences unprecedented temperature extremes, with recent heatwaves reaching up to 38-45°C in Siberia, rapid thawing of the upper layers of permafrost is becoming a defining signal of climate change [12]. As warming accelerates thaw, formerly stable frozen soils fracture into bogs, fens, and lakes, enabling previously dormant microbes to metabolize ancient organic matter. Metagenomics and biogeochemical studies now show that the identity, distribution, and metabolic strategies of microbes critically determine whether carbon is released as carbon dioxide or methane, the latter being significantly more potent. Scientists report that even in areas where deeper permafrost remains extremely cold, the upper half-metre has begun to thaw in recent decades, expanding the “active layer” where liquid water permits microbial activity. This thaw creates conditions in which ancient bacteria and viruses may reawaken or migrate into unfrozen taliks where they can persist [12].

Research at Stordalen Mire reveals that distinct thaw stages host different microbial communities and pathways of methane production. Partially thawed bogs are dominated by hydrogenotrophic methanogens, whereas fully thawed fens support communities engaging in acetoclastic methanogenesis, each responding differently to environmental change. Similarly, new studies of Arctic lakes overturn long-held assumptions by showing that deeper lake regions may release more methane than shallow zones due to temperature-sensitive methanogenic microbes [12]. Large-scale international efforts, from Siberia to Alaska and Greenland, are expanding understanding of permafrost microbiology. Recent findings show that microbes can survive millennia in frozen conditions through iron-based metabolic strategies, and that thaw-activated microbial interactions with soil minerals such as iron can accelerate carbon release. Researchers are also beginning to explore the role of viruses, which may regulate microbial populations and influence carbon processing [13]. Despite these advances, major uncertainties remain, especially concerning the vast unsampled regions of the Arctic and the complex landscape changes that accompany thaw. Nevertheless, integrating microbial genomics with remote sensing, ecological measurements, and climate modelling is beginning to expose the “mechanisms under the hood,” offering a clearer picture of how microbial dynamics may amplify future warming.  

The Thaw and Pandemics

As discussed earlier, global warming is accelerating the thawing of ancient ice layers across the Arctic, Antarctic, and high-altitude regions, creating a largely overlooked but significant threat to global public health. Beyond biogeochemical feedbacks, thawing ice can resurrect ancient pathogens. As permafrost and glacial ice melt, they release long-buried biological materials, including viruses, bacteria, fungi, archaea, and simple multicellular organisms, that have remained frozen for thousands to millions of years. Many of these microorganisms are viable, metabolically active, and capable of infecting modern hosts, while others leave behind intact genetic material that may enable their reconstruction. This review synthesizes current evidence of revived ancient microbes and outlines the potential public health risks posed by climate-induced permafrost thaw. A seminal pictorial representation (figure above) of the potential threats posed by release of ancient pathogens from permanently frozen environments was published in an article, Climate change, melting cryosphere and frozen pathogens: Should we worry…? [13].

Potential threats posed by release of ancient pathogens from permanently-frozen environments

This threat of the ancient pathogens came to academic limelight when ancient, previously unknown viruses were discovered in ice cores taken from a glacier on the north-western Tibetan Plateau in China. Scientists have identified 33 viral genera in the ice cores, of which 28 had never been documented before [14].  Similarly, recent analyses of ice cores from the Guliya ice cap in Tibet illustrate this possibility. Researchers extracted viruses from ice preserved for 520 to 15,000 years, discovering 32 viral genera, 28 of which were previously unknown [15]. Studies of glacier ice cores in Tibet have revealed dozens of previously unknown viral genera preserved for up to 15,000 years, raising questions about what other pathogens may still be entombed in frozen landscapes [15]. These findings demonstrate not only the effectiveness of new “ultra-clean” viral sampling techniques but also highlight the potential biological archives locked within glacial ice. Although the infectivity of such ancient viruses remains uncertain, the melting of these archives could, in a worst-case scenario, reintroduce long-dormant pathogens.

Scientists have successfully revived diverse microorganisms from ancient frozen environments. Viral genomes from pathogenic agents, including variola (smallpox) and the 1918 influenza strain have been identified in preserved human remains and reconstructed through modern sequencing technologies. Frozen environmental samples have also yielded both known and novel viral genera, indicating that ancient virospheres are far more diverse than previously understood [18]. Recent research demonstrates that long-dormant microbes can remain viable in frozen environments for tens of thousands of years. Furthermore, scientists have also revived several ancient viruses from Siberian permafrost, including 30,000-year-old giant viruses such as Pithovirus sibericum and Mollivirus sibericum, which regained infectivity after thawing. Though these viruses currently infect only amoebas, their survival underscores the resilience of viral particles in cold, anoxic environments [17].

While these viruses are harmless to humans, their survival demonstrates the resilience of viral particles, particularly under cold, dark, anoxic conditions typical of deep permafrost. Such environments protect virions, enabling them to persist intact for millennia. These discoveries prompt questions about whether more dangerous pathogens, such as historic smallpox variants or unknown viruses, could also be preserved in permafrost and reactivated. Many possess stress-adapted characteristics, such as enhanced DNA repair mechanisms, metabolic flexibility, and antibiotic resistance traits that predate modern antibiotic use. Their survival highlights unexpected biological resilience under extreme conditions of low temperature, nutrient scarcity, and oxidative stress. Additionally, DNA fragments from historical human pathogens, such as Mycobacterium tuberculosis, Vibrio cholerae, and Yersinia pestis, have been recovered from ancient human remains, underscoring the potential for re-emergence of eradicated or extinct infectious agents [18].

Beyond microbes, ancient ice has preserved viable fungi, amoebae, nematodes, and freeze-tolerant arthropods, expanding the range of possible biological risks associated with thawing permafrost. Well-documented events, such as the 2016 anthrax outbreak in Siberia triggered by thawed reindeer carcasses, illustrate the real-world public health consequences of this phenomenon [16].

The intricate and multidimensional relationship between climate change and the COVID-19 pandemic, was eloquently discussed at length in article published in the Environmental Sustainability journal, which argued that climate acts as both a direct and indirect force shaping the emergence, spillover, and transmission of infectious diseases. While early in the pandemic, climate was not considered a major driver of SARS-CoV-2 spread, the authors highlight that climatic variables, particularly temperature and absolute humidity, nonetheless influence the dynamics of zoonotic spillover and the subsequent propagation of respiratory pathogens [13]. The authors further explored how climate affects pathogen survival, environmental persistence, and human-to-human transmission. Absolute humidity and temperature are shown to modulate viral stability in aerosols, droplets, and on surfaces. Respiratory infections, including influenza, SARS, and MERS, historically thrive under “cold-dry” conditions, particularly in the northern hemisphere, where strong seasonal contrasts shape epidemic cycles. The study demonstrate that including temperature-dependent transmission terms significantly improves the accuracy of simulations for COVID-19 dynamics, exemplified by Japan’s winter 2020-2021 wave [17]. 

Conclusion

The review reveals that thawing permafrost constitutes a hidden carbon bomb with cascading ecological and health implications. As ice layers recede, vast ancient carbon pools, on the order of ~1,600 billion tonnes, more than twice the present atmosphere’s carbon, become accessible to microbes. Dormant bacteria and archaea can rapidly metabolize this organic matter, producing CO₂ or highly potent CH₄ depending on community composition and soil conditions. The thawing cryosphere environments should be viewed not only as a carbon source but also as incubators of ancient life. The review highlights that melting permafrost may unleash microbial forces capable of amplifying greenhouse feedbacks and unleashing dormant pathogens. This is a novel nexus: vast carbon reservoirs are rapidly oxidized by revived microbial communities, while age-old viruses and bacteria, some harbouring stress-resistant traits, could re-enter modern ecosystems. The evidence is both urgent and unprecedented, underscoring risks that are largely absent from current climate assessments.

To address this “hidden carbon bomb,” climate policies and global health strategies must adapt. Climate models should explicitly include microbially mediated emissions from thawing soils, and long-term projections must account for this positive feedback. Simultaneously, public health preparedness should incorporate the possibility of novel pathogens emerging from the Arctic: for example, developing surveillance networks in thaw-prone regions and updating pandemic plans to consider climate-triggered spillovers. Achieving this will require interdisciplinary collaboration, linking microbial ecologists, climate modellers, epidemiologists, and policy-makers, to ensure no component of climate change is overlooked. The thawing Arctic offers a clear message: microorganisms are central to Earth’s climate system. As emphasized by scientists, ignoring the microbial “unseen majority” fundamentally limits our understanding of climate change. In light of the scientific findings, integrating microbial risks into international climate agreements and One-Health frameworks is imperative. Only by confronting this microbial dimension can we hope to mitigate the compounded threats of a warmer world and safeguard both planetary stability and public health.

Author Contributions: The author conceived the concept, wrote and approved the manuscript.

Acknowledgment: The author thanks all the researchers who contributed to the success of this research work.

Funding: The author received no financial support for the research, authorship, and/or publication of this article.

Conflict of Interest: The author do not have any conflict of interest.

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