An international study, involving Professor Eric Wolff at the Department of Earth Sciences, University of Cambridge, has found that the onset of past climate changes was synchronous over an area extending from the Arctic to the low latitudes.
The Last Glacial Period, a cold interval extending from between 115,000 and 11,700 years ago, was punctuated by a series of severe climate changes: warm periods where temperatures in Greenland hiked by 8-16°Cover the course of a decade.
Data from the Greenland and Antarctic ice cores suggests that these warming events, known as Greenland Interstadials, occurred at least 25 times over this interval. Their imprint has also been observed in climate records collected from mid to low latitudes, leading scientists to question whether these widespread changes were simultaneous, or whether warming in some regions lagged behind others.
But resolving this question has proved challenging because precisely dated records of past climate are relatively rare. And dating is key. If scientists could exactly pinpoint the relative timing of warming in different regions, they could answer whether the climate changed synchronously.
The study, published in Science and led by University of Melbourne PhD student, Ellen Corrick, uses detailed climate data from stalagmites (speleothems) to compare the timing of climate changes between regions. Stalagmites take in detailed information on regional temperature and rainfall as they grow, and they can also be dated accurately, often to decadal resolution, using the uranium-thorium technique.
Corrick compiled climate data from 63 speleothem records collected from caves across Asia, Europe and South America - a dataset amounting to 20 years’ of published research from scientific teams around the world. The onset of many Greenland Interstadials was clearly recognisable in the speleothem data, each event marked by a shift in the contents of stable oxygen isotope, δ18O.
To test if the changes were synchronous, the team used statistical methods to compare the age of onset for the interstadials. Once they were sure that intraregional changes were simultaneous, the team looked at the relative timing of interstadials between Asia, Europe and South America. The wider comparison showed that, out of the 25 interstadials studied, 23 were synchronous.
According to Professor Eric Wolff, the findings “provide confirmation of a persistent but, until now, unsubstantiated assumption that climate changes between the tropics and the Arctic were synchronous.”
The team went on to compare their speleothem data with model simulations of future abrupt climate changes. “An interesting feature of this study is how well the climate model outputs agree with the stalagmite data. This gives us increased confidence in the climate models we’ve built”, said Professor Xu Zhang from Lanzhou University China, who conducted model experiments at the Alfred Wegener Institute in Germany.
The findings shed light on the patterns and timing of these warming phases, also known as Dansgaard-Oeschger events. But their cause, whether external factors, such the ice sheet height, greenhouse gases, meltwater and volcanism, or internal oscillations in Atlantic Ocean circulation, remains, as yet, an open question.
E. Corrick et al. ‘Synchronous timing of abrupt climate changes during the last glacial period.’ Science (2020). DOI: 10.1126/science.aay5538
Adapted from a press release by The University of Melbourne