Scientists have warned that the collapse of the Atlantic Meridional Overturning Circulation (AMOC), a critical ocean current system, may already be unavoidable. The AMOC plays a vital role in regulating global climate by transporting heat, nutrients, and carbon.
A new study suggests there is a 10% to 24% chance that this system has already reached a "point of no return." The risk escalates significantly with delayed climate action; if the world does not begin a path toward net-zero emissions until 2100, the probability of an inevitable collapse rises to 80%.
The AMOC is driven by the sinking of cold, salty water in the North Atlantic. This process pulls warmer, nutrient-rich waters northward, significantly influencing the climate of Europe. However, melting glaciers from Greenland are introducing freshwater into the North Atlantic, diluting the seawater and making it less dense, which researchers believe is disrupting this sinking mechanism. Studies indicate the AMOC has already weakened by approximately 15% since the mid-20th century due to climate change.
In their modeling, researchers analyzed 21 scenarios based on varying levels of Greenland ice melt and emissions reduction. In the most optimistic scenario, where greenhouse gas emissions peak in 2025 and Greenland's ice melt contributes minimally to sea-level rise, the chance of an inevitable AMOC collapse is 10%. However, current research suggests more realistic ice melt scenarios, contributing up to 274mm to sea-level rise by 2100, carry a 23% risk of collapse even if emissions begin to decrease immediately.
The consequences of an AMOC collapse could be severe. Researchers predict rapid cooling in the Northern Hemisphere, potentially making winters in the UK up to 7°C (12.57°F) colder on average. Conversely, the Southern Hemisphere could experience warming of over 10°C (18°F) in Antarctic regions, threatening ice sheets and glaciers and potentially increasing global sea levels.
Beyond temperature shifts, a collapse could lead to significant changes in rainfall patterns, intensified winter storms in certain areas, rising sea levels along the North Atlantic coast, and widespread disruption to agriculture, marine ecosystems, and fisheries. Impacts on tropical rainfall systems, including African and Asian monsoons, could affect food production for hundreds of millions of people.
Scientists emphasize that once the AMOC tipping point is crossed, simply reducing emissions to previous levels may not be enough to restart the current. The primary method to mitigate the risk is to prevent crossing that threshold by rapidly achieving net-zero emissions. The study indicates that there is typically an 84-year delay between a collapse becoming inevitable and the current actually failing, though this timeframe can shorten if emissions are not curbed promptly after commitment to action. The researchers stress that reducing global emissions as quickly as possible is the only way to decrease the risk of catastrophic climate events like AMOC collapse.