Often referred to as a “conveyor belt” that redistributes warm water from the tropics to the Atlantic Ocean, the Atlantic Meridional Overturning Circulation (AMOC) plays an important role in regulating the Earth’s systems (Rahmstorf 2024; Richardson 2008). This circulation process ensures that temperatures are stabilized, weather patterns are regulated, and ecosystems are flourishing. However, scientists are becoming increasingly worried by early signs indicating a weakening circulation and a potential collapse of AMOC due to increased anthropogenic activities. Such a turn of events could potentially disrupt ecosystems, accelerate climate change, change weather patterns and drastically increase sea-level rise (Rahmstorf 2024). To better understand the significance of this system, let us explore AMOC’s role in climate sciences, the ongoing scientific debate surrounding it, and why AMOC’s collapse matters.
The AMOC is a primary component of the global ocean flow, and part of the greater thermohaline circulation. At its core, this conveyer belt is driven by water density gradients caused by variations in salinity and temperature (Vallis 2011). In the equator, the surface water is predominately warmer than other regions due to the amount of direct sunlight it receives from the Sun. The AMOC then plays an important role in distributing this concentrated heat by transporting the warm water up toward the north (Kuhlbrodt et al. 2007; Vallis 2011). As the warm water reaches the North Atlantic, it begins to cool and sink into the deep ocean at a depth of around 2,000 to 3,000 meters due to its temperature change and salinity concentration (Rahmstorf 2024). The mechanisms of the AMOC are important because it not only distributes heat but carries and stores dissolved carbon in the deep ocean.
Given its importance in the Earth’s systems, the AMOC and its potential collapse has become a topic of interest among the scientific community and the general public. In the past century, there have been multiple observations that have indicated that the AMOC has been weakened between 15 and 20 percent (Le Bras et al. 2023). According to the general scientific community, there are “tipping points” or critical thresholds in systems that when exceeded will cause the collapse or slowdown of said system (Rahmstorf 2024; Ritchie et al. 2021). Because the AMOC is dependent on high salinity concentrations and warm surface waters, there are concerns that climate change will disrupt these mechanisms by introducing freshwater into the North Atlantic region. Freshwater input from precipitation or melting ice has the ability to dilute the ocean’s salinity and decrease the water’s density. This poses a problem, as this will affect the efficiency of deep-water formation and decrease the amount of dissolved carbon stored in the deep ocean.
However, not all those within the scientific community agree on this assessment and argue that the AMOC will most likely weaken but will not collapse anytime soon (Marotzke 2023). Other arguments center on the use of current climate models and their inability to capture the complex dynamics between the ocean and atmosphere. Climate models are computer-based representations of the Earth used to understand and predict the behavior of climate processes over time. These models can be used to assess the introduction of freshwater in the North Atlantic and can help us answer the questions of when the tipping point would occur or what would be necessary to offset this trajectory. Conversely, modeling the AMOC is challenging as it involves capturing fine-scale process that are often difficult to capture within a global model.
Although there is general disagreement on when or if the tipping point will occur, there is an overall consensus among the scientific community that the collapse of the AMOC would have devastating consequences on the Earth’s systems. Beyond altering weather patterns and increasing sea-level rise, the collapse of AMOC has the ability to impact certain regions more than others. For instance, the AMOC brings water up to the North Atlantic region and this is what causes certain countries in Europe to have warmer temperatures. If the AMOC were to collapse, countries like the United Kingdom and Germany would experience harsher and colder weather conditions that could disrupt their water and food source availability (Rahmstorf 2024). The slowdown of the AMOC would also cause an accumulation of water along the US east coast, putting those who reside within Miami and New York at risk for severe flooding. In summary, the AMOC is an important part of the Earth’s climate system, and it highlights the importance of addressing climate change and improving climate modeling to predict and mitigate its effects.
Lopez's paper explores whether the "conveyor belt" of ocean currents, which plays a crucial role in regulating global temperatures and weather patterns, is slowing down. Understanding changes to the AMOC is critical, as a slowdown could have significant impacts, including harsher winters in Europe and disruptions to tropical climates, highlighting the importance of studying this vital component of Earth's climate system.