The ~4.2–3.9 ka BP abrupt aridification and cooling event (Zanchetta et al., 2015; Weiss, 2016) is recognized in many locations across the globe, but its causes, precise timing, characteristics and quantification remain enigmatic. A 3-day international workshop on this topic was held at the Dipartimento di Scienze della Terra (Università di Pisa, Italy), 10–12 January 2018, and attended by ~60 people. This special issue will include individual papers presented at the meeting and regional syntheses subsequently developed by those in attendance.