Scientist's Opinion on Climate Change and Hard Ticks (Ixodidae).

Tick-borne diseases account for a substantial proportion of the global incidence of infectious diseases, and their recent expansion has been increasingly associated with climate change. Nevertheless, previous studies have produced heterogeneous and often inconclusive results, largely due to differences in spatial scale, variable selection, and limited integration of climatic, ecological, and host-related drivers. Here, we assess the modeled impact of climate trends on the global distribution patterns of ticks parasitizing humans and livestock, rather than changes in tick abundance or pathogen transmission. This study is not an evaluation of human or animal contact rates with ticks. Using the largest curated compilation of georeferenced tick records available to date (213,513 records from 138 Ixodidae species), we adopt a global, climate-centered perspective based on the Holdridge life zones framework. The study characterized current climatic niches of tick genera and projected changes in suitability under future climate scenarios for 2040, 2060, 2080, and 2100. Our results reveal a strong association between tick occurrence patterns and large-scale gradients of temperature and atmospheric water balance, while precipitation plays a comparatively minor role. Projections indicate increasing climatic suitability for human-biting ticks at higher northern latitudes, concurrent with declining suitability across parts of central and southern Africa. By integrating modeled suitability with human population projections and livestock distributions, we estimated future changes in exposure risk. Although local processes such as tick abundance and pathogen prevalence are beyond the scope of this study, our findings provide a coherent global synthesis of how climate change may reshape tick distributions and associated risks.