Recurrent transitions to Little Ice Age-like climatic regimes over the Holocene

Samuli Helama,Markus Stoffel,Vladimir V Matskovsky,Phil D Jones,Laura Arppe,Kari Mielikäinen,Pekka Nöjd,Richard J Hall,Mauri Timonen,Markku Oinonen

doi:10.1007/s00382-021-05669-0

Abstract

Holocene climate variability is punctuated by episodic climatic events such as the Little Ice Age (LIA) predating the industrial-era warming. Their dating and forcing mechanisms have however remained controversial. Even more crucially, it is uncertain whether earlier events represent climatic regimes similar to the LIA. Here we produce and analyse a new 7500-year long palaeoclimate record tailored to detect LIA-like climatic regimes from northern European tree-ring data. In addition to the actual LIA, we identify LIA-like ca. 100–800 year periods with cold temperatures combined with clear sky conditions from 540 CE, 1670 BCE, 3240 BCE and 5450 BCE onwards, these LIA-like regimes covering 20% of the study period. Consistent with climate modelling, the LIA-like regimes originate from a coupled atmosphere–ocean–sea ice North Atlantic-Arctic system and were amplified by volcanic activity (multiple eruptions closely spaced in time), tree-ring evidence pointing to similarly enhanced LIA-like regimes starting after the eruptions recorded in 1627 BCE, 536/540 CE and 1809/1815 CE. Conversely, the ongoing decline in Arctic sea-ice extent is mirrored in our data which shows reversal of the LIA-like conditions since the late nineteenth century, our record also correlating highly with the instrumentally recorded Northern Hemisphere and global temperatures over the same period. Our results bridge the gaps between low- and high-resolution, precisely dated proxies and demonstrate the efficacy of slow and fast components of the climate system to generate LIA-like climate regimes.

Highlights

Major climate episodes have interrupted the ongoing interglacial period (Denton and Karlén 1973; Bond et al 2001; Mayewski et al 2004; Wanner et al 2011)
Tree-ring samples of such subfossil remains and living Scots pine (Pinus sylvestris L.) trees have been previously utilised for reconstructions of summer temperature and cloud cover based on the stable carbon isotope values (δ13C) (Helama et al 2018a), tree-ring width (TRW) (Helama et al 2010) and maximum latewood density (MXD) chronologies (Matskovsky and Helama 2014)
The MXD based temperatures were available from 1 CE, whereas the reconstructions based on tree-ring δ13C and TRW were available from 5500 BCE (Helama et al 2010, 2018a)

Summary

Introduction

Major climate episodes have interrupted the ongoing interglacial period (Denton and Karlén 1973; Bond et al 2001; Mayewski et al 2004; Wanner et al 2011). The latest of these episodes, the ‘Little Ice Age’ (LIA), has excited much interest with extensive evidence from a broad range of early instrumental and documentary sources and environmental proxies (Lamb 1995; Grove 2004). A regime of cold events has been described between 300 and 900 CE (Wanner et al 2011; Helama et al 2017a, b), this interval being further punctuated by an episode of abrupt, synchronous, multi-decadal (Larsen et al 2008; Helama et al 2017b) or even centennial (Büntgen et al 2016; Matskovsky and Helama 2016) cold climate anomalies across a collection of Northern Hemisphere (NH) proxy sites around the mid-sixth century

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