Disentangling the causes of the 1816 European year without a summer

Andrew P Schurer,Davide Zanchettin,Simon F B Tett,Stefan Brönnimann,Tim Cowan,Claudia Timmreck,Gabriele C Hegerl,Jürg Luterbacher

doi:10.1088/1748-9326/ab3a10

Abstract

The European summer of 1816 has often been referred to as a ‘year without a summer’ due to anomalously cold conditions and unusual wetness, which led to widespread famines and agricultural failures. The cause has often been assumed to be the eruption of Mount Tambora in April 1815, however this link has not, until now, been proven. Here we apply state-of-the-art event attribution methods to quantify the contribution by the eruption and random weather variability to this extreme European summer climate anomaly. By selecting analogue summers that have similar sea-level-pressure patterns to that observed in 1816 from both observations and unperturbed climate model simulations, we show that the circulation state can reproduce the precipitation anomaly without external forcing, but can explain only about a quarter of the anomalously cold conditions. We find that in climate models, including the forcing by the Tambora eruption makes the European cold anomaly up to 100 times more likely, while the precipitation anomaly became 1.5–3 times as likely, attributing a large fraction of the observed anomalies to the volcanic forcing. Our study thus demonstrates how linking regional climate anomalies to large-scale circulation is necessary to quantitatively interpret and attribute post-eruption variability.

Highlights

We apply state-of-the-art event attribution methods to quantify the contribution by the eruption and random weather variability to this extreme European summer climate anomaly
By selecting analogue summers that have similar sea-levelpressure patterns to that observed in 1816 from both observations and unperturbed climate model simulations, we show that the circulation state can reproduce the precipitation anomaly without external forcing, but can explain only about a quarter of the anomalously cold conditions
This study finds that the atmospheric circulation associated with the Sea-level pressure (SLP) pattern in the summer of 1816 is estimated to cause only about a quarter of the cold anomaly observed

Summary

Introduction

Global temperatures were exceptionally low in 1816, and it was probably the coldest year for at least the last 250 years (Crowley et al 2014). In addition large volcanic eruptions have been shown to lead to a reduction in global precipitation (Iles et al 2013), a shift of the Inter Tropical Convergence Zone away from the hemisphere of maximum forcing (which can have a considerable effect on monsoon rainfall; Stevenson et al 2016) and can wetten some dry regions (Iles and Hegerl 2015). They induce dynamic changes in the large-scale circulation of both ocean and atmosphere (Zanchettin 2017). The eruption of Mount Tambora is very likely to have had a profound impact on a global scale (Raible et al 2016), causing widespread extreme climate fluctuations throughout the world in its aftermath and the following years

Methods

Results

Conclusion