'Cold blob' caused by climate change weakening Gulf Stream with potentially dire consequences for Derry and Donegal climate

New research has found that the Gulf Stream which has a key influence on the climate of Derry and Donegal is at its weakest point in over a thousand years.

Friday, 5th March 2021, 1:53 pm

Scientists from the ICARUS Climate Research Centre at Maynooth University, Potsdam Institute for Climate Impact Research (PIK), and University College London have found evidence that the slowdown of the Gulf Stream - formally known as the Atlantic Meridional Overturning Circulation (AMOC) - is associated with the development of a 'cold blob' in the middle of the North Atlantic off Ireland.

This, they say, is weakening the flow of warm ocean currents from the Equator and Caribbean to Ireland, which keeps Derry relatively warm for our northern latitude.

The Gulf Stream keeps Derry and Donegal warm relative to our northerly latitude.

The researchers used so-called proxy data – taken mainly from natural archives like ocean sediments or ice cores – reaching back hundreds and hundreds of years to reconstruct the flow history of the Gulf Stream System.

Alarmingly, they found consistent evidence that its slowdown in the 20th century is unprecedented in the past millennium and it is likely linked to human-caused climate change.

“The Gulf Stream System works like a giant conveyor belt, carrying warm surface water from the equator up north, and sending cold, low-salinity deep water back down south. It moves nearly 20 million cubic meters of water per second, almost a hundred times the Amazon flow,” explained Prof Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research (PIK), initiator of the study to be published in Nature Geoscience.

Previous studies by Prof Rahmstorf and colleagues showed a slowdown of the ocean current of about 15 percent since the mid of the 20th century, linking this to human-caused global warming.

“Instead of relying just on one data set, we used a combination of several different and largely independent proxy indicators to reconstruct the evolution of the AMOC over the past 1600 years,” said lead author Dr Levke Caesar, of the ICARUS Climate Research Centre, Maynooth University in Ireland, and guest scientist at PIK.

A 2019 special report on the oceans of the Intergovernmental Panel on Climate Change (IPCC) concluded with medium confidence ‘that the Atlantic Meridional Overturning Circulation (AMOC) has weakened relative to 1850–1900.’

“The new study provides further independent evidence for this conclusion and puts it into a longer-term paleoclimatic context,” Prof Rahmstorf said.

The consequences of the AMOC slowdown could be manifold for people living on both sides of the Atlantic, as Dr Caesar explained: “The northward surface flow of the AMOC leads to a deflection of water masses to the right, away from the US east coast. This is due to Earth’s rotation that diverts moving objects such as currents to the right in the northern hemisphere and to the left in the southern hemisphere. As the current slows down, this effect weakens and more water can pile up at the US east coast, leading to an enhanced sea level rise.”

In Europe, a further slowdown of the AMOC could imply more extreme weather events like a change of the winter storm track coming off the Atlantic, possibly intensifying them.

"If we continue to drive global warming, the Gulf Stream System will weaken further -- by 34 to 45 percent by 2100 according to the latest generation of climate models,” concludes Prof Rahmstorf.

“This could bring us dangerously close to the tipping point at which the flow becomes unstable.”