Those who scoffed at the swiftness with which the world was plunged into an ice age in the film The Day After Tomorrow may need to rethink their disbelief with new research showing that such a scenario may not be so far from the truth. A new study reveals that switching off the North Atlantic circulation can force the Northern hemisphere into a mini ‘ice age’ in a matter of months rather than the tens of years indicated by previous research.
Around 12,800 years ago the northern hemisphere was hit by a mini ice-age, known by scientists as the Younger Dryas, and nicknamed the “Big Freeze”, which lasted around 1300 years. Geological evidence shows that the Big Freeze was brought about by a sudden influx of freshwater, when the glacial Lake Agassiz in North America burst its banks and poured into the North Atlantic and Arctic Oceans. This vast pulse, a greater volume than all of North America’s Great Lakes combined, diluted the North Atlantic conveyor belt and brought it to a halt.
Without the warming influence of this ocean circulation temperatures across the Northern hemisphere plummeted, ice sheets grew and human civilization fell apart. Previous evidence from Greenland ice cores has indicated that this sudden change in climate occurred over the space of a decade or so. Now new data shows that the change was amazingly abrupt, taking place over the course of a few months, or a year or two at most.
Using a mud core taken from an ancient lake, Lough Monreach, in Ireland, the researchers have created the highest resolution record of the Big Freeze event to date. Using a scalpel layers were sliced from the core, just 0.5mm thick, representing a time period of one to three months.
Carbon isotopes in each slice reveal how productive the lake was, while oxygen isotopes give a picture of temperature and rainfall. At the start of the Big Freeze their new record shows that temperatures plummeted and lake productivity stopped over the course of just a few years.
Meanwhile, their isotope record from the end of the Big Freeze shows that it took around two centuries for the lake and climate to recover, rather than the abrupt decade or so that ice cores indicate. “This makes sense because it would take time for the ocean and atmospheric circulation to turn on again,” says researcher William Patterson, from the University of Saskatchewan in Canada.
Looking ahead to the future Patterson says there is no reason why a “Big Freeze” shouldn’t happen again. “If the Greenland ice sheet melted suddenly it would be catastrophic,” he says.
The study was carried out by the European Science Foundation EUROCORES program ‘Histories from the North – environments, movements, narratives’, which was comprised of 38 individual research teams from Europe, Russia, Canada and the USA.