Icebergs in the Ship Canal, Polar bears roaming on Deansgate?
New research looking at ocean currents has raised the possibility that global warming could plunge Western Europe into a 1,000 year mini ice age
During an abrupt global cold snap nearly 13,000 years ago, the Gulf Stream ocean current shifted further north, temporarily disrupting eastern Canada’s oceanic ecosystems, a process which could happen again as the climate changes
Research published in Nature Communications, reconstructed the history of the ocean current using marine sediments recovered off the east coast of Canada.
The team found that during a time of rapid and intense climatic change known as the Younger Dryas about 12,900 years ago, the Gulf Stream shifted hundreds of miles to the north, bringing it closer to the coast of Nova Scotia.
The Gulf Stream transports warm tropical waters northward and plays a major role in regulating climate around the North Atlantic. The shift would have initially warmed the waters surrounding Nova Scotia, likely disrupting local marine ecosystems. The effect would have lasted for the first few hundred years of the Younger Dryas, until cold fresh water from growing sea-ice from further north would have ultimately covered the warmer current, insulating it from the land and atmosphere.
The Younger Dryas was an abrupt cold snap that happened while Earth’s climate and oceans were warming following the end of the last Ice Age. Scientists are concerned because climate models predict that the present warming climate and oceans could lead to similar tipping points in the coming decades.
Lead author Fangjingcheng Zhu, who did the research at UCL and is currently at the University of Southampton, said: “Our research shows how the many different components of the Atlantic circulation system are all interconnected and can be abruptly altered during climate change. This is the first geological evidence that the Gulf Stream moved northward when the deep currents of the Atlantic weakened and is likely do so again in the future.”
The Younger Dryas was a sudden and significant dip in global temperatures that lasted a little over a thousand years, caused by Earth warming up following the last ice-age. Over less than a century, global mean temperatures abruptly plummeted about 0.6 degrees Celsius, though regions of the Northern Hemisphere saw annual mean temperatures drop by as much as 10 degrees Celsius.
The abrupt change was likely brought about by a switch in the strength of different branches of the ocean currents running throughout the Atlantic Ocean that are known collectively as the Atlantic Meridional Overturning Circulation (AMOC).
The AMOC plays a critical role in regulating Earth’s climate. It acts like a conveyor belt, transporting heat northward from the tropics and helping to keep Europe temperate. The Gulf Stream is a core part of the AMOC, where warm water from the Gulf of Mexico travels north along the east coast of North America then across the Atlantic towards Europe.
Scientists had previously known that when the currents of the AMOC changed, it reduced the heat transfer to the far north of the Atlantic Ocean. This resulted in sea-ice expanding off the UK, causing mean annual temperatures across continental Europe and much of North America to drop by up to 6 degrees Celsius.
Scientists are concerned about the possibility that the planet could face a similar abrupt change to the AMOC. Climate models predict that warming North Atlantic waters will become less dense and less able to sink and circulate, reducing the strength of the AMOC. Without this transport mechanism, less ocean heat from the tropics will reach Northwest Europe, cooling its climates.
Scientists think that if the AMOC weakens in the future, the Gulf Stream will again shift northwards, having a similarly disruptive effect on the region’s climate and ecosystems.
Senior author Professor David Thornalley (UCL Geography) said: “This study improves our understanding of how different parts of the North Atlantic circulation system interact during abrupt climate change. It’s likely that ocean currents are facing more disruption in the future, and with a more detailed picture of what happened in the past, we can know what kind of changes to expect in the future.”
