A new study lead authored by a Yale postdoctoral associate warns that excess greenhouse gases in the atmosphere may cause the collapse of an extensive undersea current, leading to significant climate changes.
The Atlantic Meridional Overturning Circulation is an undersea system that carries warm water northward, and returns colder water to the south. The general consensus of the climate science community is that the AMOC is experiencing a gradual decline, though the severity of future slowdown is contested, according to Wei Liu, a postdoctoral associate who works in the Yale Department of Geology and Geophysics.
Led by Liu, the researchers have determined that in actuality, most climate models have a common bias that causes them to understate the changes the AMOC will undergo as climate change progresses.
“The AMOC is one of the most important circulations in the climate system,” said Jiang Zhu, a Ph.D. candidate at the University of Wisconsin-Madison and a co-author of the study. “If it is dead, it is believed that the Northern Hemisphere will be a lot colder than it is currently.”
The heat the AMOC carries north is believed to be partially responsible for the relatively mild climate in Europe, compared to other places at the same latitude, Zhu said. If the current shuts off, Europe’s temperatures could drop dramatically.
The paper predicts other changes in climate systems in the event of an AMOC collapse, including dramatic changes in both the amount and distribution of precipitation, according to Zhengyu Liu, a professor of atmospheric and oceanic sciences at the University of Wisconsin-Madison.
The researchers predict that a collapse in the AMOC will lead to a southward movement of the rain belt above the tropical Atlantic, which will affect the rainfall in many nations located near or on the equator.
In the Northern Hemisphere, there will be marked increases in sea ice due to the decrease in the circulation of warm water. According to the corrected climate model the researchers used, the collapse of the AMOC and the onset of these changes will take place approximately 300 years after the carbon dioxide levels in the atmosphere are double their 1990 value.
“Winter is going to be much more expansive, and it is sure to have a huge impact on marine life,” Liu said. While the conditions resulting from the disruption of circulation will not be as severe as represented in the popular climate science disaster film, “The Day After Tomorrow,” the actual changes will have serious consequences for many living creatures, as well as human populations.
In order to correct the bias in current climate models, the researchers used what is known as a flux adjustment approach, in which they modify the climate model to represent the AMOC more realistically, Wei Liu said. The adjustment counteracts the inclination of a climate model toward a stable AMOC, so that said model accurately reflects the circulation’s observed instability.
However, this means of altering widely accepted climate models with what Liu calls a “patch” is not without controversy. While many in the climate science community have praised the researchers for their work in identifying the decline of AMOC as a major player in the climate’s future, others have taken issue with the methodology, claiming that reliable results cannot be obtained from a model that uses a “patch,” according to Zhu.
“The problem is that this method is not perfect,” Wei Liu said. “The optimal way to correct this bias would be to create an improved model. But so far, this is the best we can do.”
In order to demonstrate the accuracy of the findings, Liu plans to test the “patch” with a variety of other climate models, aside from the one used in the study. Until a more complete model of the relationship between the climate and the AMOC is discovered, Liu is confident that the predictions in this report represent the effects of greenhouse gases on the AMOC to an acceptable degree of precision.
Thermohaline circulation is commonly referred to as the ocean’s conveyer belt.