Common ragweed (Ambrosia artemisiifolia) is an invasive alien species in Europe producing pollen that causes severe allergic disease in susceptible individuals 1 . Ragweed plants could further invade European land with climate and land-use changes 2,3 . However, airborne pollen evolution depends not only on plant invasion, but also on pollen production, release and atmospheric dispersion changes. To predict the e ect of climate and land-use changes on airborne pollen concentrations, we used two comprehensive modelling frameworks accounting for all these factors under high-end and moderate climate and land-use change scenarios. We estimate that by 2050 airborne ragweed pollen concentrations will be about 4 times higher than they are now, with a range of uncertainty from 2 to 12 largely depending on the seed dispersal rate assumptions. About a third of the airborne pollen increase is due to on-going seed dispersal, irrespective of climate change. The remaining two-thirds are related to climate and land-use changes that will extend ragweed habitat suitability in northern and eastern Europe and increase pollen production in established ragweed areas owing to increasing CO 2 . Therefore, climate change and ragweed seed dispersal in current and future suitable areas will increase airborne pollen concentrations, which may consequently heighten the incidence and prevalence of ragweed allergy.Common ragweed is native in North America. Since the end of the nineteenth century it has invaded large regions in Europe 4,5 and also parts of Australia, South America and East Asia 6 . The sensitization of the human population to ragweed pollen is increasing in many countries 7 . In Europe, its established presence is at present largely limited to several areas in the [42 • N-47 • N] latitudinal band (Pannonian plain, northern Italy and southeastern France) and in areas with disturbed land, such as agricultural areas or along roads and railways. However, there is a high potential for further spread given that suitable, although not yet invaded, habitats are substantial 8,9 . Plant density may also further increase in established infested areas. Factors determining the rate of spread of ragweed plants within its current climatic niche include seed dispersal due to natural or anthropogenic processes (for example, spread through contaminated crop seeds), land-use change (which would provide changes in disturbed land areas) and the efficiency of ragweed eradication policies. Climate change may further impact the spread of ragweed by altering the climatic niche determined by physiological thresholds or affecting cropping patterns 5,10,11 . Ragweed airborne pollen concentrations depend not only on plant infestation, but also on phenology, pollen production, release, dispersion and atmospheric transport. Recent modelling efforts 12-15 have led to increasingly successful simulations of airborne pollen concentrations. Although previous work was mostly devoted to short-term forecasts to inform sensitized populations, the maturity of the mode...

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