Human-induced habitat loss rates exceed baseline rates across islands worldwide

Islands harbour disproportionately high biodiversity and endemism yet are among the world's most threatened ecosystems. Habitat loss is a major driver of this decline, but its magnitude is difficult to interpret on its own: human-induced loss can only be evaluated relative to the long-term natural variability preceding human arrival. Here, we compare human-induced habitat loss rates (HumHLr) with natural baseline habitat loss rates (BaseHLr) across 43 volcanic oceanic islands spanning eight archipelagos worldwide. HumHLr was estimated since first human arrival using two complementary proxies of natural habitat: island-specific vegetation data (local proxy) and the globally standardised Human Modification Index (global proxy). BaseHLr combined the two dominant long-term natural processes reducing habitat on volcanic islands: sea-level rise since the Last Glacial Maximum (SeaHLr) and Holocene volcanism (VolHLr). Our results indicate that HumHLr exceeded BaseHLr by approximately one order of magnitude on nearly all islands (median ratios: 18.6 global proxy, 15.4 local proxy), and was significantly higher than each baseline component, SeaHLr and VolHLr, under both proxies. Within the baseline, sea-level rise contributed more to habitat loss than volcanism, which was restricted to a few geologically active islands. Overall, these findings show that contemporary habitat loss on islands far outpaces the geological processes that shaped island environments over millennia, providing a reference for assessing extinction risk and prioritising conservation.