The Hunt for Holocene Abrupt Climate Change

Abrupt Climate Change (ACC) is one of the biggest unknowns of the modern climate system, posing a critical risk to ecosystems and human lives. Climate models struggle to simulate ACCs, underestimating the amplitude of climate variability at decade-plus timescales, and at identifying tipping points with significant accuracy. Paleoclimate records are therefore critical in assessing the magnitude, spatial footprint and impact of ACCs. However, the detection of ACCs in individual paleoclimate studies exceeds its prevalence in statistical summaries. Could this reflect confirmation bias in individual studies, statistical limitations in syntheses, or a language barrier between methodologies? We propose a distinction between an "impact sphere" where the climate impact of ACC is of unusual magnitude, and a "detection sphere" where the climate impact of ACC is detectable but not unusual. This framework will aid paleoclimate inferences and climate modelling of ACCs and help discussions on ecosystem disturbance and societal upheavals, both past and future.