The last ice age persisted for over 100,000 years. An eternity bound by ice for any stretch of the imagination, but this long winter was not completely frozen in stillness.
During the last glacial period, which ended about 12,000 years ago, climate change existed as a powerful phenomenon, as it is now, albeit for different reasons.
Throughout the ice age, a series of episodes of abrupt warming punctuated the cold, sending each of them temperatures (up to 16 degrees Celsius) in temporary heat waves that erupted for decades before disappearing.
These sudden phenomena, called Dansgaard-Oeschger events, occurred dozens of times over the last 100 millennia of the Last Glacier. But what caused their lives?
“Many studies have attempted to answer this long-standing question: what part of the climate system changed first when these approximately 30 abrupt climate changes [began]? says Emilie Capron, an ice core scientist at the University of Copenhagen in Denmark and the University of Grenoble in France.
“Was it, for example, ocean currents in the North Atlantic, wind and rainfall patterns in the northern hemisphere, or the spread of sea ice in the Arctic that triggered climate change?”
Studio author Emilie Capron with a thin, polished piece of ice core. (Sepp Kipfstuhl)
If there is a pattern that precipitates these mysterious warm-ups, it will remain hidden for now.
In a new study, Capron and his team found that when the Dansgaard-Oeschger events unfolded, a series of climatic transitions occurred almost in unison, probably each influencing the other and without any discernible trigger, similar to the fall of a house of cards. an invisible streak.
To find out, the researchers analyzed two giant ice cores pierced from the Greenland ice sheet: epic columns of compressed snow that stretch up to 3 kilometers long.
The nuclei retain numerous chemical signals from ancient climatic conditions established in prehistory, including isotope relationships that reveal past temperatures and gas bubbles that show atmospheric composition, among many other clues.
According to the researchers, the data on the ice core we have and complementary climate simulations led by the team suggest that the diversity of coincident factors combine in a relatively close proximity to create the events of Dansgaard-Oeschger and it is not yet possible to know with certainty which of these underlying mechanisms could prevent others or be more fundamentally important.
“There may not be a single sequence of changes that represent Dansgaard-Oeschger warm-ups or a single trigger for these abrupt changes,” the authors write in their article.
“The emerging image of Dansgaard-Oeschger warmings is one in which the components of the climate system are so close that it may not be possible to resolve significant shunts and lags between them and, as a result, it may be difficult to find a single sequence of ‘events in proxy data that can adequately describe all the abrupt climatic transitions of the last glacial. “
Either way, some of the features of abrupt transitions are common between events: one of them is the level of sea ice cover, which is currently declining rapidly.
Of course, we’re not in an ice age right now, so no one is saying exactly that a Dansgaard-Oeschger event is about to unfold.
However, as we well know, our environment is changing rapidly in the midst of the current climate crisis, and factors such as sea ice, which have been deeply involved with the abrupt calamities of the past, can have very important potential triggers that we do not yet have. understand it completely.
“The results emphasize the importance of trying to limit climate change, for example by reducing anthropogenic emissions of CO2 and other greenhouse gases, both to reduce predictable and gradual climate change and to reduce the risk of climate change. sudden future, ”says co-author and climate physicist Sune Olander Rasmussen of the University of Copenhagen.
“If you don’t want the domino tiles to be mastered, it’s best not to push too hard on the table they’re on.”
The findings are reported in Communications on Nature.