evidence: The climate of the past millennium was marked by substantial decadal and centennial scale variability in the Northern Hemisphere1. Low solar activity has been linked to cooling during the Little Ice Age (AD 1450–1850; ref. 1) and there may have been solar forcing of regional warmth during the Medieval Climate Anomaly2,3,4,5 (AD 950–1250; ref. 1). The amplitude of the associated changes is, however, poorly constrained5,6, with estimates of solar forcing spanning almost an order of magnitude7,8,9. Numerical simulations tentatively indicate that a small amplitude best agrees with available temperature reconstructions10,11,12,13. Here we compare the climatic fingerprints of high and low solar forcing derived from model simulations with an ensemble of surface air temperature reconstructions14 for the past millennium. Our methodology15 also accounts for internal climate variability and other external drivers such as volcanic eruptions, as well as uncertainties in the proxy reconstructions and model output. We find that neither a high magnitude of solar forcing nor a strong climate effect of that forcing agree with the temperature reconstructions. [...] Ammann, C. et al. Solar influence on climate during the past millennium: Results from transient simulations with the NCAR Climate System Model. Proc. Natl Acad. Sci. USA104, 3713–3718 (2007).