Year: 2024
Type: article
Abstract: 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.Identifying ACCs is particularly important in the Holocene [1].Once thought to be relatively quiescent, significant low-frequency climate variability is now recognised as a common feature of the Holocene [2].With near-modern boundary conditions and high data density, Holocene paleoclimate records of ACCs are a potential goldmine of information for understanding tipping points in the climate system.Further, multi-annual to multi-centennial changes in temperature and rainfall variability are frequently implicated in societal upheavals and transitions via freshwater availability and crop growth [3].Commonly invoked drivers of Holocene ACCs include freshwater pulses to the North Atlantic, solar variability and clusters of volcanic eruptions.The largest ACC of the Holocene, which occurred 8.2 kyr BP (the 8.2 ka event) is associated with freshwater pulses to the North Atlantic from icesheet melt and/or a glacial lake outburst.Large singular and clusters of volcanic eruptions are now identified as significant drivers of multi-annual to decadal scale climate anomalies [4].However, internal variability in the climate system is also frequently implicated in Holocene ACCs.ACCs may therefore be forced or unforced.The 4.2 ka event (4.26 to 3.97 kyr BP) [5], labelled a 'Global Megadrought', is implicated in societal upheavals across the northern hemisphere mid-latitudes, drawing substantial interest from paleoclimate and archaeological fields.However, it has no smoking gun driver so it is unclear whether it could be a forced ACC or an example of internal climate variability.While the 4.2 ka event has been identified in many paleoclimate records, statistically rigorous syntheses don't identify it as having an unusually large magnitude or a coherent spatial signal in the Eastern Mediterranean/Middle East [6], the Indian Ocean [7], the East Asian Summer Monsoon region [8] or globally [9,10].This holds across both high-resolution, selective syntheses, and low-resolution, inclusive syntheses.What is behind the discrepancy?Are individual
Source: PLOS Climate
Authors: Nick Scroxton, Nicholas McKay
Institutions: University College Dublin, Northern Arizona University
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $2,400
OpenAlex ID: W4405609716