Continental-scale temperature variability during the past two millennia

Past global climate changes had strong regional expression. To elucidate their spatial-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the last one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the 19th century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between 1580 and 1880 CE, punctuated in some regions by warm decades during the 18th century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the last 30-year period (1971-2000 CE), the area-weighted average reconstructed temperature was likely higher than anytime in nearly 1400 years.