You may remember the film "The Day After Tomorrow" as a sci-fi thriller, but climate scientists working with the IPCC warn that it might be more realistic than once thought.
Melting glaciers in the Arctic already threaten the AMOC in a serious way. Freshwater is less dense than salt water, meaning that instead of sinking to the bottom of the current and returning down south, it remains close to the surface. This keeps warm salty water from making it down to the bottom to become warmed, effectively shutting down the ocean’s conveyor belt.
2015 is on course to be one of the hottest years on record. Extended heat waves, droughts, and wildfires plagued drier regions, while areas right below Iceland and Greenland in the Arctic are experiencing some of their coldest recorded temperatures. According to researchers from the Potsdam Institute for Climate Impact Research and Penn State University, this reflects a slowdown in the global conveyor belt. Melting freshwater from massive glaciers at the poles has prevented the Gulf Stream from brining warm water toward the north, resulting in unseasonably cold temperatures.
The AMOC continues to run, but research reveals that it is in fact slowing down. Researchers worry that with continued warming and slowing of this essential current, certain climates will race toward a “tipping point” that could result in catastrophic damage to places that weren’t expecting it.
If the global conveyor belt were to actually stop, Europe would likely get colder while coastal North America would likely experience higher sea levels and rougher storms. New York and Boston could face a serious risk of flooding and coastal erosion, particularly in storm surges created by large hurricane-like storms.
The IPCC reported in 2014 that it was unlikely that the AMOC would shut down completely before the end of the century, but it is still subject to some serious changes. According to the most recent climate report, “it is very likely that the MOC, based on currently available simulations, will decrease, perhaps associated with a significant reduction in Labrador Sea Water formation, but very unlikely that the MOC will undergo an abrupt transition during the course of the 21st century. At this stage, it is too early to assess the likelihood of an abrupt change of the MOC beyond the end of the 21st century, but the possibility cannot be excluded. The few available simulations with models of different complexity instead suggest a centennial slowdown. Recovery of the MOC is simulated in some models if the radiative forcing is stabilised but would take several centuries; in other models, the reduction persists.”