Biodeterioration of built heritage in the context of climate change and atmospheric pollution: Toward transdisciplinary conservation strategies.

The built heritage -encompassing monuments, historic buildings and sculptural ensembles- is increasingly threatened by the synergistic impacts of climate change, atmospheric pollution and biological activity. This review critically analyses current understanding of the mechanisms driving the biodeterioration of built heritage, focusing on calcareous materials (e.g., limestone, marble and lime-based mortars), which are both widespread in built heritage and highly susceptible to degradation. We examine how environmental drivers -such as elevated humidity, temperature fluctuations, and pollutant deposition (SOₓ, NOₓ, particulate matter)-trigger complex physicochemical and biochemical reactions that compromise structural stability and aesthetic integrity. The review explores the metabolic strategies of biodeteriative organisms (fungi, algae, cyanobacteria), the interactions of pollutants and mineral substrates, and the consequent formation of salts, black crusts and corrosion products. We highlight the role of biomonitoring as a methodological and interpretive bridge linking atmospheric pollution to biodeterioration processes. In addition, we discuss emerging interdisciplinary methodologies - including functional metagenomics, microbial network analysis, and metabolomic profiling -and introduce the Function-Based Biodegradation Risk Assessment model, extended into a Multi-Level Risk Assessment Framework that connects microbial functionality, material diagnostics, and climate modeling. We contend that safeguarding built heritage in a changing climate requires transitioning from static, material-centred diagnostics to integrated, predictive frameworks that link microbial ecology, materials science, and climate dynamics, providing the basis for adaptive and anticipatory conservation strategies.