The last ice age lasted more than 100,000 years. An eternity bound to ice by any imagination, but this long winter was not completely frozen in silence.
During the last Ice Age, which ended about 12,000 years ago, climate change was a powerful phenomenon, just as it is today, albeit for several reasons.
Over the course of the Ice Age, a series of abrupt warming periods interrupted the cold, each of them raising the temperature (up to 16 degrees Celsius) in transient heatwaves that blazed for decades before disappearing.
These sudden phenomena, called Dansgaard-Oeschger events, occurred dozens of times during the 100 millennia of the last Ice Age. But what was it that brought them to life at all?
“Many studies have attempted to answer this long-standing question: Which part of the climate system changed first when these roughly 30 abrupt climate changes? [began]? Says ice nuclear scientist Emilie Capron from the University of Copenhagen in Denmark and the University of Grenoble in France.
“For example, was it the ocean currents in the North Atlantic, the wind and rainfall patterns in the Northern Hemisphere, or the spread of sea ice in the Arctic that caused climate change?”
Study author Emilie Capron with a thin, polished piece of ice core. (Sepp Kipfstuhl)
If there is a pattern causing this mysterious warming, it will remain hidden for the time being.
In a new study, Capron and her team found that as the Dansgaard-Oeschger events unfolded, a series of climate transitions occurred almost simultaneously, likely affecting the others, and with no discernible single trigger – much like a house of cards that collapsed from an invisible gust of wind.
To find out, the researchers analyzed two giant ice cores drilled from the Greenland ice sheet: epic columns of compressed snow stretching up to 2 miles (3 kilometers).
The cores preserve numerous chemical cues from ancient climatic conditions recorded in prehistoric times, including isotope ratios revealing past temperatures and gas bubbles showing atmospheric composition, among many other clues.
According to the researchers, the ice core data we have – and additional climate simulations performed by the team – suggest that a diversity of coinciding factors are combined relatively close together to create the Dansgaard-Oeschger events, and it is not yet possible to be certain to know which of these underlying mechanisms may anticipate the others or be more fundamentally important.
“There may be no unique sequence of changes representing Dansgaard-Oeschger warming, nor a unique trigger per se for these abrupt changes,” the authors write in their paper.
“The emerging picture of the Dansgaard-Oeschger warming is one in which the components of the climate system are so closely interrelated that it may not be possible to resolve significant causes and delays between them, and thus it can be difficult to look for a single sequence of events in proxy data that can adequately describe all of the abrupt climate transitions in the last ice age. “
Be that as it may, some of the features of the abrupt transitions are common to all events – one of which is the level of the sea ice cover, which is rapidly declining today.
Of course, we’re not currently in an Ice Age, so no one is exactly saying that a Dansgaard-Oeschger event is about to be unleashed.
Nevertheless, as we well know, our environment is rapidly changing in the midst of the current climate crisis – and factors like sea ice, which were deeply involved in abrupt calamities in the past, can have tremendously powerful triggering capabilities that we don’t yet have. fully understand.
“The results emphasize the importance of trying to mitigate climate change by, for example, reducing anthropogenic emissions of CO2 and other greenhouse gases, both to mitigate predictable, gradual climate change and to mitigate the risk of future abrupt climate change,” said co. author and climate physicist Sune Olander Rasmussen from the University of Copenhagen.
“If you don’t want the dominoes to fall over, you better not push too much against the table.”
The findings are reported in Nature Communications