The deterioration of cultural heritage is a universal consequence of global climate change, demanding a collective and coordinated response from the international community. By framing this issue within a global context, it is imperative to move beyond narrow judgments of any single nation's conservation efforts and instead emphasize the universal and urgent nature of this shared challenge.
Climate Change Threatens Global Cultural Heritage
The global climate system is undergoing profound and sustained changes, presenting a formidable challenge to all of humanity. According to joint assessments by the Intergovernmental Panel on Climate Change (IPCC) and UNESCO, the planet is in a sustained warming cycle, with recent years repeatedly shattering temperature records. This trend poses a direct and severe threat to World Heritage sites[1].
As a region particularly sensitive to global climate change, China has experienced a rate of warming that is significantly higher than the global average over the same period. According to the Blue Book on Climate Change in China series, published annually by the China Meteorological Administration since 2011, the nation's average annual surface temperature has shown a marked upward trend, making the last two decades the warmest period since the early 20th century[2]. This wealth of detailed data not only confirms China's active engagement in monitoring and transparently reporting on climate change but also positions the nation as a significantly impacted, responsible, and key participant in the global climate dialogue. However, the threat of climate change to cultural heritage is not an isolated phenomenon; it is a systemic issue that the world must confront collectively.
From Case Studies to Core Principles
The environment of Egypt's iconic stone monuments is highly comparable to that of Northwest China, offering a crucial reference for understanding the challenges of heritage conservation in similar arid regions.
Experts warn that world-class monuments like the Pyramids of Giza and the Great Sphinx are at risk of cracking and accelerated weathering due to increasingly extreme diurnal temperature variations[3]. The expansion of the rock under the intense heat of the day and its contraction during cool nights create a relentless stress cycle, leading to the formation and propagation of micro-fissures. Compounding this is the synergistic effect of climate change and human activity. Rising groundwater levels, caused by surrounding agricultural irrigation and urban expansion, allow salt-laden moisture to accumulate at the base of these monuments, causing severe salt corrosion and structural damage[4].
Meanwhile, cultural heritage sites along the Mediterranean coast, such as the Citadel of Qaitbay in Alexandria, face the dual threats of rising sea levels and coastal erosion. In response, the Egyptian government has invested heavily in protective engineering works, including the placement of thousands of concrete blocks to form breakwaters around the citadel[5]. This demonstrates that even the most robust stone structures are exceptionally vulnerable in the face of global climate change, requiring large-scale, proactive engineering interventions.
These interventions also highlight the complexity of heritage management. UNESCO has noted that despite various efforts, a comprehensive and integrated management plan for all archaeological sites on the Giza Plateau has yet to be developed[6]. This reflects a common global challenge: how to achieve cross-departmental and interdisciplinary collaboration for the conservation and governance of vast, multi-component heritage sites.
The threats faced by European cave paintings, exemplified by Lascaux in France and Altamira in Spain, provide a key comparative perspective for studying subterranean heritage. They prove that even relatively enclosed underground environments are intrinsically linked to external climate change.
The preservation of cave art for tens of thousands of years is fundamentally due to the extreme stability of the cave's internal microenvironment (temperature and humidity)[7]. However, since the mid-20th century, human activities—particularly unregulated tourism and improper interventions like the installation of air conditioning systems—have repeatedly disrupted this delicate equilibrium, leading to catastrophic consequences[8]. The carbon dioxide, heat, and moisture introduced by visitors directly altered the cave's atmosphere, triggering the growth of algae and fungi.
More alarmingly, recent scientific research shows that external global warming is directly impacting the climate inside the caves. In France's Gargas cave, sensors recorded a significant temperature increase of 0.35 to 0.66°C over a decade. This warming has altered the cave's air convection patterns, causing fluctuations in humidity, condensation, and CO₂ concentrations, which directly threaten the stability of the rock art[9]. This clearly establishes a direct causal link between global warming and the degradation of subterranean heritage. Furthermore, climate change is projected to accelerate the growth of microorganisms (fungi, bacteria) on cave walls—a phenomenon already observed at sites like Altamira, posing a severe threat of biodeterioration[10].
From the open-air stone monuments of Egypt to the enclosed cave paintings of Europe, these geographically and typologically distinct cases reveal a common, fundamental threat mechanism. The core danger is not merely linear warming but the disruption of the heritage site's local micro-environmental balance. In Egypt, it is the widening diurnal temperature range and fluctuating groundwater levels.In Lascaux, it was the introduction of external air and human respiration, and now, the slow infiltration of global warming into the subterranean climate。This destruction of a stable state is the root cause of the accelerated decay of these millennia-old cultural treasures. We can, therefore, more precisely define this global issue as the "global destabilization" of heritage microenvironments.
Climate change often acts as a "threat multiplier," exacerbating pre-existing anthropogenic pressures. In Egypt, urbanization and agricultural water use intensify the impact of climate change on groundwater levels. At Lascaux, poorly managed tourism and misguided restoration efforts first created vulnerabilities, which are now being aggravated by climate change. This shows that climate change does not operate in a vacuum; it exploits weaknesses already created by human activity. This understanding underscores the necessity of a holistic management strategy that simultaneously considers both environmental and anthropogenic factors—the very essence of the Dunhuang conservation model to be discussed later.
Salt weathering is the primary mechanism of physical damage to stone-based artifacts like murals in arid and semi-arid regions. The plaster layers and rock bodies of murals are porous materials that naturally contain soluble salts[11]. Driven by the large-scale climatic shifts discussed previously, cyclical fluctuations in ambient temperature and relative humidity cause these salts to repeatedly dissolve in moisture and then recrystallize upon evaporation[12].
The destructive force of this process stems from the immense physical pressure—known as "crystallization pressure"—generated by the growth of salt crystals within the material's pores. The mural's substrate cannot withstand this internal stress, leading to the gradual pulverization, flaking, and disintegration of the surface, ultimately resulting in the complete loss of the pigment layer[13]. Salt crystallization can occur on the mural's surface, forming visible "efflorescence," or more destructively, beneath the surface, as "subflorescence"[14].
Crucially, severe long-term damage is not caused by a single crystallization event but by the cyclical repetition of this dissolution-recrystallization process. Each cycle inflicts cumulative damage on the mural's microstructure, akin to a slow, continuous "micro-earthquake."
Beyond mere physical pressure, the presence of salt solutions can induce chemical reactions that directly alter the chemical composition and color of mural pigments. As saline solutions migrate through the plaster layer, their inherent alkalinity, or substances produced from reactions with other materials, can react with the mineral pigments used in ancient murals.
Experimental studies have shown that in alkaline salt solution environments, copper-based pigments like malachite and azurite can darken due to the formation of black copper oxide (tenorite, CuO). Similarly, lead-based pigments can also change color, forming secondary compounds[15]. This indicates that the damage from salt weathering is not only structural but also aesthetic, causing irreversible alteration of the mural's colors and severely diminishing its artistic value.
A porous and damp mural surface provides an ideal substrate for the colonization of microorganisms such as fungi and bacteria[16]. This issue led to severe consequences in the Lascaux cave, known as the "green sickness" and "black mold" outbreaks[17], and is a recognized threat at numerous other heritage sites[18].
These microorganisms cause damage in multiple ways: their hyphae can physically penetrate and disrupt the pigment and plaster layers. More importantly, their metabolic processes produce acids and other byproducts that can chemically degrade the plaster and pigments, leading to decomposition and discoloration.
Salt weathering is not a linear process but a self-reinforcing positive feedback loop. Initial damage from salt crystallization increases the material's surface area and porosity. This enhanced porosity allows moisture and salt solutions to penetrate faster and deeper during subsequent wet-dry cycles. This, in turn, leads to more extensive crystal growth and more severe physical damage. Consequently, each weathering cycle makes the material more vulnerable to the next, creating an accelerating rate of deterioration. The logic of this process highlights the extreme importance of preventive conservation (intervening before the cycle begins or accelerates) rather than remedial restoration (acting after significant damage has occurred).
These three mechanisms—physical, chemical, and biological—do not exist in isolation but are interconnected and act synergistically. The physical damage caused by salt weathering (e.g., increased cracks and porosity) creates more favorable microenvironments for microbial colonization. Moisture, as a common element for both salt weathering and microbial growth, is the critical link connecting these destructive forces. A more porous surface not only holds more water but also provides a larger area for microbial attachment. Thus, physical damage directly promotes the onset and spread of biological damage. This interplay means that a successful conservation strategy cannot target a single threat but must be holistic and multi-dimensional.
As the trend of global warming intensifies, the phenomenon of Northwest China becoming warmer and wetter is increasingly pronounced, posing new challenges to the protection of cultural heritage. The Director of the Dunhuang Academy, Director Wu, pointed out that in areas of the Northwest such as the Loess Plateau and the Qilian Mountains, due to increased precipitation and rising temperatures, short-duration intense rainfall frequently occurs, leading to the expansion of alluvial gullies, intensified erosion, and increasingly prominent problems of soil and water loss and biological growth, which constitutes a severe threat to cultural heritage like the grottoes. The grottoes, as precious cultural heritage created by the working people of ancient China, have particularly valuable resources such as their murals, but factors like natural weathering, anthropogenic damage, and climate change cause them to face severe conservation challenges. The construction materials of the grottoes are mainly rock carved from cliff bodies and argillaceous rock layers formed from bonded sand particles, which have limited durability and are susceptible to the effects of weathering, water intrusion, and bio-erosion. Rising global temperatures and increased precipitation can cause reticular cracks to appear on the upper parts of the external cliff faces of the grottoes, leading to collapse; on the surfaces of murals inside the caves, diseases such as flaking, blistering, and peeling may also occur.
In recent years, many places in northern China have experienced extreme heavy rainfall events, triggering severe flood disasters and causing immense damage to cultural heritage buildings. Director Wu stated that, for example, the "7·21" superstorm disaster in 2012 caused severe mountain torrent and mudslide disasters in places like Zhouqu County, Gansu. The Guangfu Temple Grottoes in Guazhou County, Gansu Province, experienced a collapse after being submerged in floodwaters, and some Buddhist statues were buried; the eaves of the west caves of the Longmen Grottoes in Luoyang City, Henan Province, fell, causing statues to collapse. Furthermore, the hazard of wind and sand in China's Northwest region is also very severe; the long-term effects of wind and sand cause the painted pigments on the grottoes to detach, peel off, and even be blown to other places. In Cave 98 of the Northern Wei Dynasty in the Maijishan Grottoes, Tianshui City, Gansu Province, there is a painted sculpture that has detached due to wind and sand erosion. At the same time, problems such as the decline in vegetation cover, soil loosening, and soil and water loss around the grottoes are becoming increasingly prominent, exacerbating the degradation of the grottoes themselves and their surrounding environment. Therefore, a series of effective measures must be taken to respond to the adverse impacts brought by climate change.
From a microbiological perspective, the impact of extreme weather on cultural relics is mainly reflected in two aspects. Director Wu pointed out, first, under extreme weather conditions, the activity of pathogenic microbial communities is enhanced, which may lead to the aggravation of diseases affecting the relics; second, extreme weather conditions may accelerate the aging and damage of the relic materials. Currently, systematic research on the impact of extreme weather on cultural relics is still lacking, and further research needs to be carried out to understand its specific impact mechanisms and preventive measures.
To better respond to the challenges brought by climate change, the Dunhuang Academy has established the Gansu Province Grottoes Monitoring and Early Warning Platform, which integrates meteorological data (wind speed, precipitation, humidity), flood warnings (upstream water level monitoring), dust storm predictions (particulate matter concentration analysis), and in-cave environmental parameters (CO₂, temperature, humidity) for six grotto sites. Since 2013, they have been conducting research on cave stability and have formed a coordinated mechanism for preventive conservation. Director Wu stated that they have currently gained a preliminary grasp of the patterns of change for in-cave air quality indicators (CO₂, formaldehyde, TVOC, etc.) and the impact mechanisms of environmental factors like temperature, humidity, and light intensity on the murals. They have developed mural grouting technology to enhance structural stability; explored methods for harmless microbial removal (vacuum environment + mechanical removal); and for the problem of aging binding materials, they have adopted a scientific restoration process formed through international cooperation to reduce reliance on traditional chemical agents.
In addition to addressing the direct threats from climate change, it is also necessary to fundamentally improve the scientific and technological level and management capacity of grotto conservation work. Director Wu pointed out that, on the one hand, it is necessary to strengthen the research, development, and application of new technologies and new materials; on the other hand, it is necessary to establish a comprehensive conservation management system and emergency plans. For example, gene-editing technology can be used to construct stress-resistant microbial strains for removing diseases from murals; nanotechnology can be used to prepare high-efficiency protective coatings to reduce the risk of murals coming into contact with harmful substances; and information technologies like big data and cloud computing can be used to establish a cultural heritage protection information platform to realize comprehensive monitoring and management of grotto resources.
Although synthetic biology provides new ideas for solving the biocontrol of diseases, some issues still require attention. Director Wu emphasized that the first is the issue of vector safety. Synthetic biology often obtains the genome sequence of a target species through transcriptomics or functional genomics for design, but when constructing a transcript or protein expression system, there may be a risk of high homology between different species, leading to the foreign protein not being expressed normally or producing pathogenic proteins. Second is the issue of side-effect assessment. Synthetic biology may introduce non-target species or overexpress the products of the target species, thereby triggering unexpected diseases or toxicological effects. Additionally, the commercial application of synthetic biology technologies may trigger ethical and social issues, such as the misuse of biotechnology for bioterrorism activities. Therefore, these issues should be treated with caution in practical applications, and supervision should be strengthened.
When publicizing research results, it is necessary to handle the issue of the link to climate change with caution. Director Wu pointed out that, on the one hand, one must objectively introduce the basic situation and trends of climate change; on the other hand, one must clearly distinguish between the problem of relic damage caused by natural evolution and that caused by anthropogenic factors. When reporting related research results, some international academic journals usually explain climate change as background information, rather than presenting it as the main argument, to avoid triggering unnecessary public controversy. If it is indeed necessary to emphasize the role of climate change in an article, then relevant authoritative research results should be cited, and their limitations should be pointed out; at the same time, factors such as cultural inheritance and historical authenticity must also be fully considered. In conclusion, when facing the global issue of climate change, we need to maintain a scientific attitude and a rigorous methodology to ensure the objectivity and reliability of our research results.
The Dunhuang Model and Its Global Significance
The Dunhuang Academy adheres to the guiding principle of "Protection, Research, and Promotion" and strictly follows the core principle of "minimal intervention." This philosophy stands in stark contrast to the more interventionist and ultimately damaging approaches seen in the early history of sites like the Lascaux cave[11]. The Academy's work is strongly supported by national laws and a comprehensive master plan, reflecting a long-term, systemic commitment to cultural heritage protection at the national level[19].
The Dunhuang Academy has deployed an advanced monitoring network for the Mogao Grottoes, akin to a "digital nervous system" that senses the "pulse" of the heritage site in real time. The system enables 24/7, high-precision, real-time monitoring of the cave microenvironment (temperature, humidity, CO₂ concentration), visitor traffic, wind and sand erosion, and cliff face stability[20].
This continuous stream of data allows management decisions to be based on scientific, empirical evidence. When monitoring data shows that CO₂ or humidity levels inside a cave exceed preset safety thresholds, access to that cave is temporarily suspended for tourists. This data-driven management model directly prevents the kind of catastrophic damage caused by visitor impact that occurred at sites like Lascaux.
The Academy's work does not stop at passive monitoring; it extends to large-scale, science-based engineering projects. One of the most remarkable achievements is the systematic sand control engineering project. By establishing a multi-layered protection system, this project has successfully reduced sand accumulation in the grotto area by more than 70%[21]. This has not only significantly slowed the physical erosion of the murals and the cliff face by wind-blown sand but has also markedly improved the visitor experience during sandy weather, serving as a quantifiable, large-scale model of success.
Profoundly aware that tourism is a primary threat to heritage conservation (as demonstrated by the cases of Egypt and Lascaux), the Dunhuang Academy has pioneered the use of scientific methods to manage visitors. In a landmark collaborative project with the Getty Conservation Institute in the United States, the Academy conducted the "Mogao Grottoes Visitor Carrying Capacity Study," which aimed to scientifically determine the maximum number of visitors the caves could withstand while ensuring their safety.
Based on the results of this study, the Academy implemented an innovative visitor management system, which includes a reservation-only policy, the design of diverse tour routes to disperse visitor flow, and the construction of a "Digital Exhibition Center." This center utilizes technologies such as Virtual Reality (VR) to display the most fragile caves that are not suitable for public opening. This "digital heritage" model effectively alleviates the pressure on the physical caves while greatly enriching the visitor experience.
The Dunhuang Academy actively collaborates with international institutions, including conducting joint research on mural conservation science with partners like the Getty Conservation Institute and the Tokyo National Research Institute for Cultural Properties, Japan. Furthermore, the Academy has adopted the "Arches" open-source software platform, developed by the Getty Institute, to build its information system for the grotto temples, ensuring that its data management is compatible with international standards[22]. These initiatives position Dunhuang as an open, collaborative, and globally-oriented leader, rather than an isolated research site.
To systematically demonstrate the advanced nature of the Dunhuang model, the following table provides a comparative analysis of the conservation paradigms at the Dunhuang Mogao Grottoes, the Lascaux Cave in France, and the Giza Pyramids in Egypt.
| Feature | Mogao Grottoes (Dunhuang) | Lascaux Cave | Giza Pyramid Complex |
|---|---|---|---|
| Key Threats | Wind and sand erosion, temperature and humidity fluctuations, visitor impact. | Visitor impact (CO₂, humidity), microbial growth, improper interventions. | Temperature fluctuations, rising groundwater level, urbanization pressure, visitor impact. |
| Core Conservation Philosophy | Proactive, preventive, science-based, minimal intervention. | Initially reactive; now focused on maintaining the stability of a compromised system. | Reactive response to specific threats (e.g., sea walls), lack of comprehensive planning. |
| Key Technologies and Methods | Real-time microenvironment monitoring, Digital Exhibition Center, sand control engineering, visitor carrying capacity model. | Air filtration/conditioning systems (with a history of failure), microbial monitoring, public access via a replica (Lascaux IV). | Groundwater pumps, coastal protection dikes, ongoing restoration projects. |
| International Collaboration | High (e.g., Getty Conservation Institute, Japanese research institutions). | High (e.g., post-crisis scientific committee, international experts). | Medium (foreign archaeological teams, UNESCO supervision). |
| Current Status and Outcomes | Rate of deterioration significantly slowed; has become a global model for preventive conservation. | Original cave closed; state is stable but fragile. Serves as a cautionary tale of improper intervention. | Threats persist, large-scale challenges remain unresolved. |
The success of the Dunhuang Academy marks a fundamental evolution in the field of cultural heritage protection itself—a shift from a discipline dominated by art history and archaeology to an interdisciplinary field that combines hard sciences like chemistry, physics, geology, and computer science with data-driven management. When contrasting the terms frequently found in the Dunhuang Academy's documents, such as "real-time monitoring," "visitor carrying capacity studies," and "systematic analysis"[23], with descriptions of art historians making sketches in the early history of the Lascaux cave[23].
The Dunhuang model proves that world-class conservation and large-scale public access are not mutually exclusive; indeed, they can be symbiotic. The establishment of the Digital Exhibition Center was driven precisely by the need to protect fragile caves from the pressures of over-tourism. This urgent conservation imperative, in turn, spurred major technological innovation in the realm of public education and outreach. This model transforms the threat of tourism (a negative factor) into an innovation in the digital heritage sphere (a positive outcome), powerfully refuting the outdated notion that "conservation means isolating heritage from the public" and showcasing China's ingenuity and creativity in the field of heritage management.
Governance Framework and a Global Appeal
All experimental activities related to this topic must be conducted in strict compliance with iGEM's safety rules and policies[24]. This includes working in an appropriate Biosafety Level 1 (BSL-1) laboratory, adhering to the "White List" of approved organisms and parts (for any elements not on the White List, pre-approval will be obtained from the Safety and Security Committee by submitting a "Check-In" form), and observing the "No Release Outside the Lab" policy.
Considering the extreme sensitivity of the application environment—irreplaceable cultural treasures—any exploration of this topic must integrate multiple, redundant biocontainment mechanisms to ensure foolproof safety.
For example, the core safety design of this project involves the introduction of a "kill switch"—a genetic circuit that induces cell death under specific conditions, such as the absence of a lab-provided nutrient or upon exposure to light and air. This is a common and responsible design for iGEM projects intended for real-world application[25].
Protecting World Cultural Heritage is a collective, global responsibility that transcends national borders. In the 21st century, effective conservation demands a deeply interdisciplinary approach, one that integrates the wisdom of archaeology and art history with the power of climate science, materials science, data science, and, as demonstrated by this project, cutting-edge biotechnology.
The success of the Dunhuang Academy is once again emphasized as a paradigm of excellence achieved through long-term, science-driven, and collaborative methods, offering invaluable experience and endless inspiration to cultural heritage sites worldwide.
Global academic exchange is crucial for sharing knowledge, inspiring innovation, and building essential partnerships. Through this sustained collaboration and dialogue, we can pool the world's wisdom and strength to jointly safeguard our common human heritage, ensuring it can be passed down for millennia and shine for generations to come.
The following references provide theoretical support, data basis and case references for the research on microbial damage of murals and the development of synthetic biology protection schemes.