21 August 2020

Proven: Historical climate changes occurred simultaneously in several parts of the world

CLIMATE

A new study published by researchers from the University of Copenhagen and partner institutions has proven that repeated and abrupt climate changes during the last ice age occurred simultaneously in South America, Southeast Asia, Europe and Greenland. Abrupt climate change can be as problematic as gradual change and we should deal with the risks associated with abrupt scenarios, suggests a UCPH researcher.

Photo collage of  stalactite caves and ice Greenland
Photo: Getty Images

A kind of domino effect — a convergence of rising temperatures and changing precipitation rates occurred across the planet during the last ice age, stretching from 120,000–11,700 years ago.

According to a study published 21'st of august 2020 in the journal Science, climate changes in several areas of the world affected each other.

"By analyzing stalactite measurements from caves in South America, Asia, Europe and ice core samples from Greenland, we are able to see that 34 of the last ice age's 37 abrupt climate changes occurred simultaneously in each of these regions. In Greenland, abrupt warming caused temperatures to rapidly increase by roughly 20 degrees on 37 occasions during the last ice age, while other regions were particularly impacted by sudden changes in precipitation patterns," explains Sune Olander Rasmussen, an associate professor at the University of Copenhagen’s Niels Bohr Institute.

"While we don't completely understand what caused these climatic changes, they are most likely the result of changes to the strength of the Gulf Stream," elaborates Rasmussen.

For many years, there has been a running assumption that climate changes spread like ripples across water, thereby affecting several areas of the planet at once. But until now, such occurrences had never been mapped accurately.

By measuring the presence of radioactive elements with known half-lives in stones from stalactite caves, as well as by counting annual layers in ice cores drilled from the Greenland Ice Sheet, the researchers were able to pinpoint when climate changes occurred.

"This is the first time that we have been able to gather so much data from across the last ice age, at so many different sites, and prove that climate change occurred simultaneously in several parts of the world — with as little as 100 years of uncertainty. When working on climate change spanning tens of thousands of years, this is considered to be very accurate," says Sune Olander Rasmussen.

We should prepare for abrupt temperature swings

While the study does not delve directly into modern day climate change, Rasmussen believes that its results are valuable for identifying the mechanisms at play today and in the possible future, vis-à-vis abrupt climate change.

"Abrupt changes in temperature or global sea level could transpire at rates that are difficult for us to adapt to. Denmark is no exception, even though we have more resources than many other countries for dealing with the problems associated," he says.

Much of the current policy agenda is based upon reducing gradual global warming. But a new agenda, one that deals with the risk of fundamentally different scenarios — abrupt climate changes — is on the way. According to Rasmussen:

"It is at least as important for us to reduce the risks associated with abrupt climate changes, as it is to work to reduce the scope of gradual climate change — just as we as a society devote considerable resources to reduce the risks of serious, yet unlikely disasters such as nuclear accidents and plane crashes."

Dating methods confirmed

Beyond cementing that the climate changes of the last ice age occurred simultaneously, the researchers were also able to confirm that their dating methods work:

"We have worked to date ice cores from the Greenland Ice Sheet by counting annual core layers for many years. The new results demonstrate that we are better at doing so than we could have ever imagined," explains Sune Olander Rasmussen.

For example, if the researchers had missed just one or two percent of the annual layers in the ice cores, they would have miscalculated by thousands of years.

“We have steered clear of major errors and find the same patterns of climate change in both the ice cores and stalactites. The number of years between each of the 37 climate changes match so well that it confirms our interpretation and counting of the annual core layers. This is important for the future of climate change research because it means that we can combine and better use ice core and stalactite data together," concludes Sune Olander Rasmussen.