• A recent study shows that 80% of UNESCO World Cultural Heritage sites are facing climate stress, with wood and stone constructions susceptible to a range of threats from extreme heat, humidity, aridity and other climatic factors.
• Researchers also found there is no single pathway toward mitigating global greenhouse gas emissions that will uniformly protect these sites.
• In addition, the team found a Global North-South divide in heritage conservation, as Global South nations do not have the same resources to preserve their cultural sites; preservation will take collective efforts.
• This story is part of The 89 Percent Project, an initiative of the global journalism collaboration Covering Climate Now.

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The Great Wall of China, Petra of Jordan, Ellora Caves of India, the traditional Ottoman Houses in Turkey — none of these world-famous historical sites can easily be replaced if damaged. Yet, each of these sits out in the open, inviting hordes of tourists every year, under alarming climate jolts.

A recent global assessment revealed that a staggering 80% of sites on the UNESCO World Heritage list are already burdened by climate stress, with nearly one in five sites (19%) constructed of key materials that are threatened, such as stone and wood.

The study found that if the world follows a “low-emission” path — where strong global action is taken to cut pollution and limit climate change to safer levels, while keeping global temperature rise below 1.5° Celsius (2.7° Fahrenheit) above preindustrial levels — about 40% of threatened sites could be protected. However, global greenhouse gas emissions are rising, with a trajectory for around 2.5-3°C (4.5-5.4°F) of warming by 2100, closer to a “medium-emission” path. Under this scenario, far fewer sites would be spared, according to the study.

In an increasingly warming world where climate change effects are growing worse each year, researchers decided to analyze the status of humanity’s most renowned historical sites made of stone and wood. The team analyzed the past (1961-91), present (2010-40) and future (2070-2100) climate risks to World Heritage sites by mapping the exposed surfaces of buildings with 3D models, which provided a site-level index of climate stress.

Interestingly, the researchers found that no single mitigation strategy could equally protect the sites due to regional and material variations, the study reveals.

Haiyang Cui, corresponding author of the study and a professor at Guizhou University in China, noted in an email to Mongabay that the key motivation for the global-level study was to conduct a material-specific assessment. “Our goal was to help countries prioritize where to save first when budgets are tight,” he said.

Buddhist monks walk up Borobudur Temple, a UNESCO World Heritage site in Indonesia. Research shows that many heritage sites, particularly those built of stone or wood, face multiple stresses due to climate change. Image by AP Photo/Yasuyoshi Chiba/Pool photo.
Visitors examine an ancient wall near Jiayu Pass, a strategic point of the Great Wall of China in northwestern Gansu province. As with many other World Cultural Heritage sites, the Great Wall is threatened by climate change. Image by AP Photo/Ng Han Guan.

Regional disparities & Global North-South divide

Among the most striking findings of the study: a stark Global North-South divide in heritage conservation.

While more than 40% of affected heritage sites are in Europe and North America, the same fragilities play out differently in the Global South.

Haiyang said that climate risks are determined by differences across climate zones, such as tropical monsoon areas, subtropical coastal regions and arid inland zones and cannot be approached from a country-specific or continent-specific lens. However, he noted that low- and middle-income countries often face greater pressure from compound climate events but have the least access to conservation resources, creating a Global North-South divide in conservation efforts and impacts.

“Temperature, humidity, and weather patterns determine climate risks,” he said. For instance, in subtropical coastal climates, such as those found in Brazil, Morocco or China, he said that problems like salt spray, erosion and storm surges are especially severe. Whereas in tropical monsoon regions like Southeast Asia, heritage sites built from stone such as Angkor in Cambodia or the Borobudur Temples of Indonesia, face constant exposure to high heat, high humidity and heavy rainfall. “Often, these climatic conditions also trigger secondary effects, such as invasive plant roots or termite activity, which may damage structures from within,” he said.

In arid regions like the Middle East, alternating high temperatures and very low humidity levels cause expansion and contraction in materials, which can lead to cracking in brick or stone buildings.

He explained a notable case in the mosque complexes of Isfahan, Iran, where delicate architectural elements are increasingly exposed to thermal stress. “Even in temperate inland Europe, recent years have brought more frequent heatwaves and dry wind events,” he noted.

Moreover, in places like the Old City of Zamość in Poland, the number of severe climate events has increased sharply, raising concern among conservation professionals, Haiyang said, explaining how stone and wood are made of fundamentally different components and react differently to climate change. “Stone dislikes sudden swings in heat and humidity, whereas wood suffers when it gets wet and then dries again, repeatedly.” The frequency of these climate jolts over the years, and the historic sites’ exposure to them, determine the stress thresholds for stone and wood.

“The type of threat varies greatly depending on local climate, and understanding this variation is essential to designing protection strategies that actually work in different parts of the world,” he noted.

Minor bleaching is seen at Lagoon Reef at the northern Great Barrier Reef, a natural site on the UNESCO World Heritage list that faces threats from climate change. Image by AP Photo/The Australian Institute of Marine Science.
This 1950 photograph from what is now the Angkor Archaeological Park in Cambodia shows the ravages of weather, time and jungle growth on the site’s temples. Recent research shows the growing threats of climate change to cultural heritage sites. Image by AP Photo/James Mills.

Challenges in heritage conservation

Haiyang said that building a global climate-heritage risk network will remain unlikely as part of larger conservation efforts due to a lack of documentation and monitoring technologies in the developing countries of the Global South.

He said that funding and advanced skills required to study heritage sites are also scarce in developing countries and suggested that to bridge this gap, high-capacity countries can contribute by offering “flying labs”: mobile expert teams that bring restoration skills, conservation technologies and training directly to under-resourced regions.

He also noted that adapting traditional knowledge in heritage conservation is sustainable and inclusive in the long run.

While the latest study focused only on wood and stone sites rather than natural heritage sites like national parks, another study published in 2024 showed that high temperatures will continue to be a major extreme climate challenge for natural heritage sites if humanity does not take effective measures to control emissions.

The study revealed that extreme weather events will pose threats to landscape structures of natural heritage sites in Spain’s Andalusia. It also emphasized that extreme ocean temperatures are causing the Great Barrier Reef in the Australian region to bleach more frequently. “If no response is taken, the Great Barrier Reef will likely experience bleaching once a year,” the study noted.

Both studies reiterate that reducing emissions is vital to any solution in heritage conservation, but it is beyond the control of local organizations, and the window of time to prevent the worst effects of anthropogenic warming is almost closing.

UNESCO notes that two-thirds of all the natural heritage sites form crucial sources of water, with half of them preventing natural hazards like floods and landslides.

Miriam Stark, a University of Hawai‘i-Mānoa professor and director of the Center for Southeast Asian Studies who extensively studied Angkor-era structures in Cambodia with the Greater Angkor Project, who was not involved in Haiyang’s study, told Mongabay that incorporating material-specific thresholds in climate risk assessments depending on local climatic conditions makes the study stand out.

“The question of who is responsible for protecting the heritage structures from climate risks often comes up. Having worked in Cambodia for 25 years, in heritage sites that we’ve deemed important, if you ask me whether Cambodia alone is responsible for protecting them, I’d say, no,” she said, adding, “Conservation of heritage sites is a collective responsibility.”

However, she emphasized that while the intervention of countries with higher funds for heritage conservation is crucial to preserving world cultural heritage, they must also leave the final decisions to regional and local governing bodies.

Banner image: A Jordanian Bedouin boy leads a tourist on a camel through the ancient city of Petra, Jordan. World Cultural Heritage sites made out of stone are at risk from the effects of severe weather and climate change. Image by AP Photo/Nariman El-Mofty.

This story is part of The 89 Percent Project, an initiative of the global journalism collaboration Covering Climate Now.

Citations:

Chen, Z., Gao, Q., Wu, Y., Li, J., Li, X., Li, X., … Cui, H. (2025). World cultural heritage sites are under climate stress and no emissions mitigation pathways can uniformly protect them. Communications Earth & Environment, 6(1). doi:10.1038/s43247-025-02603-8

Chen, G., Fu, B., Jiang, Y., Suo, X., Lai, Y., Chen, Z., … Li, B. (2024). Natural world heritage sites are at risk from climate change globally. Communications Earth & Environment, 5(1). doi:10.1038/s43247-024-01933-3