This matched with evidence from other sources, especially other tree ring records. (drtimball.com)
«Differing amplitudes resulting from borehole and tree ring climate proxies suggest that longer time scale (multidecadal and century) variability is more faithfully captured by borehole results, while the same information can be irretrievably lost in tree ring records...» (deepclimate.org)
But using tree ring records of historical precipitation the scientists calculated that the current drought is «exceptionally severe in the context of at least the last millennium.» (smithsonianmag.com)