High sensitivity of summer temperatures to stratospheric sulfur loading from volcanoes in the Northern Hemisphere

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https://www.pnas.org/doi/10.1073/pnas.2221810120

Authors 

Andrea Burke https://orcid.org/0000-0002-3754-1498 ab...@st-andrews.ac.uk, Helen M. Innes https://orcid.org/0000-0002-4003-3910, Laura Crick, Kevin J. Anchukaitis, Michael P. Byrne https://orcid.org/0000-0001-9019-3915, William Hutchison, Joseph R. McConnell https://orcid.org/0000-0001-9051-5240, Kathryn A. Moore https://orcid.org/0000-0002-9242-5422, James W. B. Rae https://orcid.org/0000-0003-3904-2526, Michael Sigl https://orcid.org/0000-0002-9028-9703, and Rob Wilson

06 November 2023

https://doi.org/10.1073/pnas.2221810120

Significance

Stratospheric sulfate aerosols from large volcanic eruptions reflect incoming sunlight and cool climate, but this process is not well quantified due to a limited observational record. Here, we take advantage of the unique sulfur isotope fingerprint imparted by UV radiation in the upper stratosphere, measuring volcanic sulfate peaks in polar ice cores to determine their climatically important stratospheric component. We find evidence that several of the coldest decades in the last two thousand years—linked with major climatic and societal disruption—were driven by a relatively small amount of stratospheric sulfate from high-latitude eruptions. This challenges the view that tropical eruptions have the largest climatic impacts and suggests enhanced climatic sensitivity to high-latitude volcanic forcing in the Northern Hemisphere.

Abstract

The 540s, 1450s, and 1600s represent three of the five coldest decades in the Common Era (CE). In each of these cases, the cause of these cold pulses has been attributed to large volcanic eruptions. However, the provenance of the eruption and magnitude of the volcanic forcing remains uncertain. Here, we use high-resolution sulfur isotopes in Greenland and Antarctic ice cores measured across these events to provide a means of improving sulfur loading estimates for these eruptions. In each case, the largest reconstructed tree-ring cooling is associated with an extratropical eruption, and the high-altitude stratospheric sulfate loading of these events is substantially smaller than previous estimates (by up to a factor of two). These results suggest an increased sensitivity of the reconstructed Northern Hemisphere summer temperature response to extratropical eruptions. This highlights the importance of climate feedbacks and processes that amplify and prolong the cooling signal from high latitudes, such as changes in sea ice extent and ocean heat content.

Source: PNAS