By Helen Street
In the movie The Day After Tomorrow (2004), AMOC and the associated Gulf Stream collapses, throwing the entire world into chaos. Scotland freezes in seconds, a superstorm annihilates Los Angeles, and New York City is inundated by water. In the movie, the planet is plunged into climate chaos overnight. While this will not occur so dramatically in real life, the potential effects of changes in ocean currents are profound.
What is the AMOC?
The Atlantic Meridional Overturning Circulation (AMOC) is a part of the ‘global conveyor belt’ which distributes heat and energy around the earth. Dense, cold, salty waters in the Northern Atlantic fall to the bottom of the ocean and travel south. The well-known Gulf Stream is a surface current that helps the AMOC transport warm water to the north, giving Europe its mild climate. At the end of the last Ice Age, the melting of ice sheets increased the freshwater content of the North Atlantic, changing the density of water in northern latitudes and leading to the collapse of the AMOC. The result was dramatic cooling in the northern hemisphere and warming in the south.
Is the AMOC breaking down today?
The topic of AMOC collapse is the subject of a highly contentious debate. The 2021 Intergovernmental Panel on Climate Change (IPCC) report claimed with medium confidence that the AMOC would not abruptly collapse before 2100, but there was high confidence in the decline of the AMOC over the 21st century for all emission scenarios. More recently, climate scientists warned the Nordic Council of Ministers that the risk of AMOC collapse was higher than the 2021 IPCC had estimated. In their letter, they claim that the tipping point of the AMOC is a possibility in the next few decades, rather than the next century. There is no clear consensus regarding the timeline of AMOC collapse, but regardless, the definite slowdown of the system which has been observed is worthy of global concern.
Global Effects of an AMOC Slowdown
The AMOC has slowed by approximately 15% since the mid-20th century and is at its weakest in over a millennium. Potential global consequences of such a slowdown include increased extreme weather conditions in Europe, North America, and North Africa, leading to heatwaves, droughts, winter storms, increased sea levels, and flooding. Increased regional variability will occur because the AMOC will no longer effectively distribute heat and energy throughout the planet. Already, over the past 10 years, the Northeast U.S. Shelf and the Gulf of Maine have warmed 99% faster than the rest of the global ocean. Additionally, in Europe from 1981-2010, droughts associated with the weakening of AMOC have cost approximately €9 billion per year to UK and EU economies.
Impact of an AMOC slowdown on UK weather
Along with the rest of Europe, the UK would experience dramatic cooling. It is estimated that in the event of an AMOC collapse, the UK average surface temperatures would decrease by 3-7ºC. This will be coupled with reduced rainfall in the summer and more storms in the winter. These storms will be of increased magnitude, bringing snowfall on the western coast and drying in the east. Eastern Scotland will be especially vulnerable to such changes. In 2022, the east of Scotland saw the driest January in 80 years, and the drought risk in the east is going to continue to increase in the future. Increased variability in weather conditions alongside sea level rise also puts St. Andrews golf courses especially at risk, with a predicted rise of 90 cm by 2100.
How would the AMOC-impacted weather affect the UK economy?
Agriculture:
The aforementioned drying trends significantly threaten agricultural production, a sector which employs 285,000 people in the UK. It has been estimated that in the event of total AMOC collapse, net primary production across the UK would be reduced by 50%, with greater impacts in the north. In 2021, Fife farmers were banned by the Scottish Environment Protection Agency (SEPA) from using water from the Riven Eden because it dropped to the second-lowest water level recorded. With less precipitation in the summer associated with the slowdown of AMOC, there will not be enough water for crops and livestock. Water catchments in Tayside and Fife may be able to collect enough rainfall to irrigate potatoes and horticulture but won’t be able to meet demand if grains require irrigation. It has been suggested that cropping systems may need to shift towards crops that require less water. Scotland’s advanced irrigation technology is likely to be more able to adapt to changing conditions than that of less developed economies which are reliant on water brought by monsoon conditions. For example, the West African Monsoon is predicted to have a shorter wet season in response to changes in the AMOC in a region that is dependent on monsoon rains for agriculture.
Fisheries:
The slowdown of AMOC and the resultant cessation of the even distribution of ocean heat will disrupt ecosystems and impact fishing. In 2023 Scottish sea fisheries employed 3,793 people and landed £652 million of sea fish and shellfish. In Scotland, the offshore waters (covering an area of 462,263 km2) owe their diversity to the influence of the warm Gulf Stream waters from the west and cool Arctic waters from the north and east. Aside from the distribution of heat, the AMOC is responsible for bringing key nutrients from the depths of the ocean. With the slowdown, fewer nutrients will be available in areas where they historically have been, impacting oceanic ecosystems. Furthermore, shifts in the seasonal patterns of ocean warming and cooling will alter salmon migration cues, creating a disconnect between the salmon’s biological requirements and the prevailing ecosystem conditions they come across. Warming patterns also affect salmon because they will have to increase migration distances to reach feeding areas. There is a lot of uncertainty surrounding the impacts of changing ocean climates on salmon and other fish populations, but it is clear that the slowdown of AMOC has the potential to provide massive detriment to the fishing economy.
Could cooler temperatures from AMOC slowdown counteract anthropogenic climate warming?
The changes wrought by the slowdown or collapse of AMOC also demonstrate the importance of the difference in terminology between “climate change” and “global warming.” While there is a general trend towards climate warming, the changing variability and patterns in precipitation and sea level rise are of greater concern and will not occur uniformly.
While it is possible that cooling resulting from the AMOC slowdown could serve to compensate for some anthropogenic climate warming (warming caused by human activity) in the UK and Europe, the greater global climate variability will have a net negative impact. Changing weather patterns and drought regions will be detrimental to agricultural production, and increased strength and frequency of storms will stress infrastructure. Regions used to rainfall will experience droughts and areas not used to rain will experience more flooding. Additionally, the increased ocean temperature in areas, such as the Atlantic along the east coast of North America, will cause sea levels to rise due to thermal expansion.
The slowdown of AMOC will also serve to accelerate climate change. The ocean is a very important ‘carbon sink,’ meaning it takes carbon dioxide out of the atmosphere. The ocean absorbs approximately 31% of carbon dioxide emissions, and it is an incredibly important resource when combatting anthropogenic climate change driven by carbon dioxide and other greenhouse gasses. The risk of a breakdown of the AMOC is that it reduces the carbon dioxide uptake. When the cold water sinks in the North Atlantic, it takes carbon dioxide into the deep ocean, and without this, the ocean would be severely limited in its ability to absorb carbon.
Concluding Thoughts:
Ultimately, the breakdown of the AMOC will not occur as drastically as in the movie The Day After Tomorrow, but the slowdown of ocean processes presents widespread risks to both the global climate and economy. If not combatted, the AMOC could collapse between a few decades and the next century. However, the problem cannot be pushed to future generations. The slowdown of the AMOC means significant changes, including but not limited to weather patterns, temperatures, sea levels, agricultural productivity, and marine ecosystems including fisheries. These changes are a symptom of greater global climate change, and thus it will not be easy to prevent the consequences of the AMOC slowdown or collapse without concentrated effort on combating climate change.
The views expressed in this article are the author’s own and may not reflect the opinions of The St Andrews Economist.