From Delhi to Venice: How World Heritage Sites are battling pollution, climate change

Acropolis of Athens, Greece

Recognised as a Unesco World Heritage Site in 1987, the Acropolis of Athens has long stood as a symbol of classical civilisation. It helped shape Western architecture and democracy. Yet its iconic white Pentelic marble monuments, including the Parthenon, Propylaia, Erechtheion, and the Temple of Athena Nike, are increasingly threatened by air pollution.

Sulphur dioxide from vehicle and industrial emissions reacts with marble to form gypsum, creating black crusts that trap airborne particles and accelerate surface erosion, particularly in areas sheltered from rain. As conservation scientists Myriam Bouichou and Elisabeth Marie-Victoire note in their 2021 article, Cleaning Historic Concrete- A Guide to Techniques and Decision-Making, these crusts are “primarily the result of the interaction between atmospheric sulphur dioxide and the marble surface”.

The Acropolis (Wikipedia)

Restoration efforts, underway since 1975, were launched to halt decades of atmospheric degradation and structural damage caused by corroding iron reinforcements from earlier repairs. Led by the Greek culture ministry’s Acropolis Restoration Service (YSMA), the programme combines meticulous documentation, replacement of corroded iron with corrosion-resistant titanium, careful cleaning of marble surfaces, and the reassembly of original architectural fragments using reversible conservation techniques.

The long-running project underscores a wider environmental challenge: preserving ancient monuments today requires not only restoration but continuous scientific monitoring and preventive conservation.

Colosseum, Rome

Drawing more than 12 million visitors every year, the Colosseum is among the world’s most visited cultural landmarks and a lasting symbol of Roman engineering. Recognised as a Unesco World Heritage Site in 1980, the nearly 2,000-year-old amphitheatre is now facing issues of rising temperatures, vehicle emissions, urban pollution, and mass tourism— affecting its travertine and tuff stone. Heat-induced thermal expansion creates microcracks, while humidity fluctuations and heavy rain contribute to surface erosion and material decay.

Further, fluctuations in humidity, coupled with more frequent heavy rainfall, encourage salt crystallisation, water infiltration, and biological growth such as algae and mould, all of which weaken the masonry and increase surface erosion.

As conservation scientist Paolo Camuffo notes in Climatic Change (2001), “Black crusts, mainly composed of gypsum with embedded soot and fly ash, form on the parts of monuments where rainwater cannot wash away the particles of pollutants deposited there.” These crusts hasten chemical weathering and stone decay.

Recognising these risks, the Parco archeologico del Colosseo, an autonomous archaeological park managed by Italy’s culture ministry, launched a comprehensive monitoring programme in 2018. Combining satellite imagery, ground-based diagnostics, digital documentation, historical records, and regular visual inspections, the initiative later evolved into SyPEAH (System for the Protection and Education of Archaeological Heritage), a digital platform developed with the Italian Space Agency to detect structural changes and support preventive conservation.

As project leaders Alfonsina Russo, Irma Della Giovampaola, and Alessandro Coletta, among others, note, the initiative seeks to “reduce vulnerability and increase resilience through the use of low-impact technologies”, reflecting a shift from periodic restoration to continuous, preventive conservation of heritage.

Venice, Italy

Among the many stories told to visitors in Venice is that the city belongs as much to the sea as it does to its people. Today, climate change is turning that poetic image into a growing conservation challenge. Recognised as a Unesco World Heritage Site in 1987, Venice and its lagoon are increasingly threatened by rising sea levels and frequent acqua alta (high-tide flooding). The city’s gradual subsidence, estimated at about 23 cm over the past century, has made flooding increasingly frequent, threatening its historic buildings, public spaces, and tourism.

In Flooding and Environmental Challenges for Venice and Its Lagoon (2011), edited by environmental scientists and researchers Carlo Campostrini, Paolo Canestrelli, David M. Bird, and Paolo Marani, warns, “Time may be running out for Venice,” as rising water levels increase the risk of catastrophic flooding similar to the devastating flood of 1966.

Venice (Wikipedia)

Constructed largely of porous brick and limestone, many of Venice’s structures absorb saltwater during floods. Experts explain that as the water evaporates, salt crystals form within the masonry, accelerating erosion and structural decay. Intense rainfall and humidity lead to further deterioration.

To safeguard the city, Italy has invested in the MOSE (Modulo Sperimentale Elettromeccanico) project, a system of more than 75 mobile flood barriers designed to isolate the Venetian Lagoon from exceptionally high tides. Alongside engineering interventions, Unesco has emphasised the need for long-term protection that will ultimately depend on adapting to accelerating sea-level rise alongside reducing global greenhouse gas emissions.

Rapa Nui National Park (Easter Island), Chile

Set on a remote volcanic island nearly 3,500 km off the coast of mainland Chile, Rapa Nui National Park is best known for its nearly 900 monumental moai statues and ceremonial ahu platforms. It is a reminder of the island’s Polynesian civilisation, which flourished between the 10th and the 16th centuries.

However, rising sea levels, stronger storm surges, and accelerating coastal erosion are destabilising the volcanic coastline and the ahu platforms on which many statues stand. Researchers warn that the ahu at Hanga Roa and Tahai are among the most vulnerable to the storms in the Southern Ocean, making it particularly vulnerable to wave attack and shoreline recession.

Rapa Nui (Wikipedia)

As environmental researchers L. Quilliam, R Cox, P Campbell and M Wright note in their 2014 study, Coastal Climate Change Impacts for Easter Island in 2100,  “Easter Island is susceptible to the impacts of climate change through higher frequency storm surges with increasing coastal inundation and beach shoreline recession.” Beyond the monuments themselves, climate change threatens freshwater availability, agriculture, and the broader cultural landscape that has sustained the Rapa Nui people for centuries.

From Delhi to Athens, Rome, Venice and Rapa Nui, the world’s heritage sites are confronting a shared climate crisis. Scientists argue that preservation requires more than archaeological expertise; it requires coastal management, continuous monitoring, and climate adaptation. However, the burden lies not only with the government but also with the hundreds of thousands of tourists who visit these sites every year.