Relative impacts of human-induced climate change and natural climate variability

Assessments of the regional impacts of human-induced climate change on a wi de range of social and environmental systems are fundamental for determinin g the appropriate policy responses to climate change(1-3). Yet regional-sca le impact assessments are fraught with difficulties, such as the uncertaint ies of regional climate-change prediction(4), the specification of appropri ate environmental-response models(5), and the interpretation of impact resu lts in the context of future socio-economic and technological change(6). Th e effects of such confounding factors on estimates of climate-change impact s have only been poorly explored(3-7). Here we use results from recent glob al climate simulations(8) and two environmental response models(9,10) to co nsider systematically the effects of natural climate variability (30-year t imescales) and future climate-change uncertainties on river runoff and agri cultural potential in Europe. We find that, for some regions, the impacts o f human-induced climate change by 2050 will be undetectable relative to tho se due to natural multi-decadal climate variability. If misleading assessme nts of-and inappropriate adaptation strategies to-climate-change impacts ar e to be avoided, future studies should consider the impacts of natural mult idecadal climate variability alongside those of human-induced climate chang e.