Global warming risks dehydrating and inflaming human airways

Global warming increases water evaporation rates from planetary ecosystems. Here, we show that evaporation rates encountered during human breathing in dehydrating atmospheres promotes airway inflammation and potentially exacerbates lung diseases. Continuum mathematical analysis predicts that water evaporation thins airway mucus layers and compresses epithelial cells during tidal breathing. Experiments using human tracheal-bronchial cells confirm that exposure to air with progressive degrees of dryness (relative humidities of 95%, 60% and 30% at 37°C) causes the mucus layer to progressively thin (by 5%, 35%, and 58%). Associated compression of epithelial cells elevates secretion of inflammatory cytokines ( $\text{TNF-α}$ , IL-33, and IL-6). Exposing mice with a muco-inflammatory phenotype to intermittent dry air for 7 days results in histopathological changes and alteration of inflammatory infiltrates. Together with climate model simulations, these findings suggest that most of the United States will be at elevated risk of airway inflammation by the latter half of this century.