Was millennial scale climate change during the Last Glacial triggered by explosive volcanism?

James U.L Baldini,Richard J Brown,Jim N Mcelwaine

doi:10.1038/srep17442

Abstract

The mechanisms responsible for millennial scale climate change within glacial time intervals are equivocal. Here we show that all eight known radiometrically-dated Tambora-sized or larger NH eruptions over the interval 30 to 80 ka BP are associated with abrupt Greenland cooling (>95% confidence). Additionally, previous research reported a strong statistical correlation between the timing of Southern Hemisphere volcanism and Dansgaard-Oeschger (DO) events (>99% confidence), but did not identify a causative mechanism. Volcanic aerosol-induced asymmetrical hemispheric cooling over the last few hundred years restructured atmospheric circulation in a similar fashion as that associated with Last Glacial millennial-scale shifts (albeit on a smaller scale). We hypothesise that following both recent and Last Glacial NH eruptions, volcanogenic sulphate injections into the stratosphere cooled the NH preferentially, inducing a hemispheric temperature asymmetry that shifted atmospheric circulation cells southward. This resulted in Greenland cooling, Antarctic warming, and a southward shifted ITCZ. However, during the Last Glacial, the initial eruption-induced climate response was prolonged by NH glacier and sea ice expansion, increased NH albedo, AMOC weakening, more NH cooling, and a consequent positive feedback. Conversely, preferential SH cooling following large SH eruptions shifted atmospheric circulation to the north, resulting in the characteristic features of DO events.

Highlights

With DO event initiation can seemingly occur on human timescales, identifying the underlying cause of such abrupt climate change and considering these forcings in a modern context is critical
We suggest that the Toba eruption initiated southward Intertropical Convergence Zone (ITCZ) migration by inducing a Northern Hemisphere (NH)-Southern Hemisphere (SH) temperature asymmetry, which resulted in more South American Monsoon (SAM) rainfall but reduced rainfall in the NH low latitudes, consistent with speleothem-based evidence (Fig. 1), and identical to the response to NH eruptions over the last 500 years
We propose that the positive feedbacks following NH eruptions (e.g., NH sea ice expansion, NH continental glacier expansion, increased NH albedo, and Atlantic Meridional Overturning Circulation (AMOC) weakening) prolonged the climatic response to the Toba eruption by several hundred years, not dissimilar to recent results suggesting that Little Ice Age cooling was initiated by NH volcanism in the 13th Century but was sustained over hundreds of years by a positive feedback involving sea ice and oceanic circulation[24]

Summary

Introduction

With DO event initiation can seemingly occur on human timescales, identifying the underlying cause of such abrupt climate change and considering these forcings in a modern context is critical. Recent research demonstrates that this same asymmetric cooling effect occurred following the injection of sulphate aerosols into the stratosphere following large volcanic eruptions over the last 100 years (based on instrumental data)[20] and 500 years (based on stalagmite rainfall proxy data)[21].

Results

Conclusion