Defining the Little Ice Age

Abstract. The "Little Ice Age" (LIA) is possibly the best-documented climatic anomaly of the past. A wide range of datasets portrays a harsh climate that worsened living conditions, primarily in terms of cooler temperatures, for people across Europe sometime during the last millennium. Regardless of the vast amount of data covering the LIA, there is presently no consensus concerning its spatial manifestation (was it regional or global?), its temporal constraints (when did it start and end?), or the broad-scale dynamics associated with it (what mechanisms did it involve?), although there is no shortage of suggestions. Based on a new compilation of data reflecting atmospheric circulation at both high and low latitudes, we show that the LIA lasted for roughly 400 years (∼1400–1800 AD). During this period at least four major atmospheric circulation systems on Earth co-varied on decadal to centennial timescales: Northern Annular Mode (NAM), Intertropical Convergence Zone (ITCZ), El Nino-Southern Oscillation (ENSO) and West African Monsoon (WAM). This pattern of convergence suggests that a strong coupling between these circulation systems was an important pre-condition for the realisation of the LIA.