Analysis: The Atlantic between Ireland and Canada, which gives us our mild climate, is behaving strangely and is the only location on the earth's surface that has cooled
By Gerard McCarthy, Maynooth University; Tomas Buitendijk, UCD; Audrey Morley, University of Galway; Chris Bean, DIAS
The Atlantic Meridional Overturning Circulation (AMOC) is the system of ocean currents that moves warm water northwards in the Atlantic and cycles water back at depth to the south. This ocean conveyor belt releases the heat that gives Ireland a warmer climate than is typical for maritime climates at the same latitude. It also plays an important role in moving heat and carbon to the deep ocean. When the AMOC weakens, heat is no longer being buried in the deep waters of the North Atlantic, leading to a relative cooling in that region. If it shuts off completely, the likely results could be strong cooling in winter, reduced rainfall especially in summer, and increased storminess.
While recent research has shown that this scenario could well occur in future centuries, an AMOC shutdown is still considered unlikely this century. Yet, even in the much more probable scenario of AMOC weakening, drier summers and stormier conditions will exacerbate the impacts of climate change, even if warming is muted. This combination of altered rainfall patterns and increased storminess would have significant impacts on Ireland's agriculture and on society more generally. Our way of life is adapted to the current mild and wet climate, meaning rapid changes can wreak havoc on Ireland as we know it.
Isn’t that the Gulf Stream?
The Atlantic ocean current system is often inaccurately referred to as the Gulf Stream, which is only one of its components. The idea that the Gulf Stream has cultivated a particularly mild and wet national climate has become deeply entrenched in the cultural identity of Ireland. For example, in James Joyce’s Ulysses (1922), protagonist Stephen Dedalus refuses to take a bath as he argues that "all Ireland is washed by the gulfstream". In other words, he believes the Irish weather will sort him out soon enough. Ireland’s image abroad has also been influenced by descriptions of its temperate oceanic climate. Take Nobel Laureate Heinrich Böll’s Irish Journal (1957), which inspired many German tourists to visit the island and includes a chapter on the arrival of Irish rain after its long journey across the Atlantic.
From the UK's National Oceanography Centre, What is the AMOC and why is it so important?
Despite this seemingly stable connection between climate and cultural identity, scholars in both Ireland and the United States have found evidence of longstanding public concern that the Gulf Stream may collapse as a result of human-induced climate change. Catastrophe fiction from the late Victorian era already imagines how such an event would fundamentally alter the landscape and society in both Ireland and Britain. This trend of imagining climatic disasters related to the Gulf Stream continues into the present—albeit at a global scale—with popular dystopian works like Roland Emmerich’s The Day After Tomorrow (2004) and Kim Stanley Robinson’s Fifty Degrees Below (2005). While any changes to the AMOC are unlikely to be as dramatic as depicted there, it is now increasingly clear that the system is slowing down.
Is the AMOC collapsing?
The heightened public concern around an AMOC collapse is not just fuelled by science fiction. In recent years, more scientific research has raised concerns about the stability of the AMOC. Indeed, the Atlantic between Ireland and Canada is behaving strangely. Since the beginning of the 20th century, this region of the Atlantic is the only location on the surface of the earth that has cooled.
Looking at this cooling as an indicator of AMOC health, the temperatures in this region were not just unusual because they were cooling, but also because they were beginning to wobble, with some decades warmer and some cooler than the global average. This 'wobbling' is a concerning indicator, as it can suggest an impending collapse. Much like when in the pub you see someone wobbling on a bar stool, it is not a surprise when later they fall off. This phenomenon is known as critical slowing down: when a system loses stability, it is more prone to collapse. Based on sea surface temperatures, it appears that the Atlantic is indeed "wobbling on the barstool".
How can we best observe the ocean current changes?
However, the picture derived from sea surface temperatures is incomplete, as these are not direct observations of the AMOC itself. Direct observations of the ocean currents consist of strings of moorings deployed on long cables—such as the RAPID project, stretching from the Bahamas to the Canary Islands—that monitor the AMOC by measuring water density and flow speeds across all depths. These direct observations only exist since the early 21st century, which is a relatively brief timeframe for understanding dynamic ocean systems. They show a weakening, but not a rate of weakening consistent with an imminent collapse. Consequently, a significant aspect of AMOC research involves extending this observational record further back in time.
Scientists close this observation gap by combining marine climate archives, such as sediment cores extracted from the seafloor, with contemporary observations. In layers, just like in ice cores or tree rings, these sediment cores provide an indirect natural archive of AMOC change going back hundreds to millions of years. These longer records are vital for gaining a comprehensive understanding of the AMOC's natural behaviour, its inherent stability, and crucially, how it responded to past climate changes.
From these archives, it has been discovered that the AMOC is not always stable and can abruptly weaken, not only during ice ages, but also during distant past climates that were as warm as today. This deep historical perspective allows for the building of more robust and accurate predictive models and the identification of early warning signs of potential future shifts or slowdowns in the AMOC.
Read more: Are hot Irish days worsening due to climate change?
In such a complex system of currents, making direct measurements remains essential for identifying early warning signs. This presents a major challenge: capturing all components of the overturning circulation requires observations from both surface and deep waters. Yet, obtaining continuous, large-scale, long-term data from the deep Atlantic is enormously difficult and costly. The challenge intensifies if AMOC change accelerates, which would demand even more frequent observations. Current observation systems require huge moorings and ships to service them, ensuring their accuracy, but also making them costly and slowing data availability. Additional observations, particularly at depth, are urgently needed to improve the efficiency of these systems.
A promising development lies in trans-oceanic optical fibre telecommunications cables, which rest on the seafloor and crisscross the Atlantic. The glass fibres are sensitive to environmental changes such as temperature, pressure, and small motions of the cable. Emerging cable monitoring techniques now allow for the detection of tiny stretches in optical fibres, caused by shifts in seafloor pressure, temperature, and flow. Although still in the early stages, combining these cable measurements with machine learning tools offers a potential new horizon for detailed spatial and temporal monitoring of the AMOC.
Ireland's climate crossroads
Ireland's mild and wet climate, intrinsically linked to its cultural identity and historically nurtured by the AMOC's heat transport, now confronts a period of significant uncertainty. The increasing reality that this vital ocean system is slowing down signals a future where drier summers and stormier conditions become more prevalent. Such alterations threaten to profoundly affect Ireland. A proactive approach is key, requiring enhanced scientific research and subsequent policy integration to better understand these risks.
By leveraging deep historical records from marine climate archives and advancing direct measurements, including innovative methods like monitoring trans-oceanic optical fibre cables, we can enhance our ability to build more robust and accurate predictive models and identify early warning signs of potential future shifts or slowdowns.
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Gerard McCarthy is a physical oceanographer based in the ICARUS climate research centre in Maynooth University. Tomas Buitendijk is an interdisciplinary researcher studying the sociocultural dimensions of coastal and marine landscape change. He is based in the Earth Institute at University College Dublin. Audrey Morley is a paleoceanographer based in Geography and the Ryan Institute at the University of Galway. Chris Bean is a Geophysicist based at the Dublin Institute for Advanced Studies. All authors are affiliated with the iCRAG Research Ireland Centre for Applied Geosciences.
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
