The Atlantic Meridional Overturning Circulation (AMOC) may have been gradually losing stability over the past one hundred years, according to a new study by Niklas Boers from the Potsdam Institute for Climate Impact Research.
The results of this study are as concerning as they are surprising. The AMOC, which includes the Gulf Stream, is responsible for much of the temperatures in Europe and has an important influence on the overall global climate.
Until now, the collapse of this ocean system had seemed unlikely. If it’s the new reality, there could be dire consequences.
“The Atlantic Meridional Overturning really is one of our planet’s key circulation systems,” said Boers. “We already know from some computer simulations and from data from Earth’s past, so-called paleoclimate proxy records, that the AMOC can exhibit – in addition to the currently attained strong mode – an alternative, substantially weaker mode of operation. This bi-stability implies that abrupt transitions between the two circulation modes are in principle possible.”
The AMOC redistributes heat and it’s predicted that if it collapses, there could be major changes to weather patterns. According to Britain’s Met Office, a collapse of the AMOC would increase cooling of the Northern Hemisphere, cause an overall drop in precipitation over Europe and North America, and lead to a shift in monsoons in South America and Africa,
“The difference is crucial. Because the loss of dynamical stability would imply that the AMOC has approached its critical threshold beyond which an abrupt and potentially irreversible transition to the weak mode could occur,” said Boers.
Previous research has shown that the AMOC is weaker than it’s been at any point in the last thousand years. It’s been unclear whether this weakness is due to a slowing in pace or a loss of stability. Unfortunately, the research suggests that it’s the latter. According to Boers, the culprit seems to be warming.
“Most evidence suggests that the recent AMOC weakening is caused directly by the warming of the northern Atlantic ocean. But according to our understanding, this would be unlikely to lead to an abrupt state transition.”
“Stability loss that could result in such a transition would be expected following the inflow of substantial amounts of freshwater into the North Atlantic in response to melting of the Greenland ice sheet, melting Arctic sea ice and an overall enhanced precipitation and river runoff,”
Direct observation of the AMOC for the last 100 years is non-existent. However, scientists can look at salinity patterns in the Atlantic to look at temperatures and overall climate. Unfortunately, this evidence suggests that indeed AMOC may be close to collapse.
The research is published in the journal Nature Climate Change.