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Climate Change: North Atlantic Warming Hole could disrupt the jet stream

Credit: NASA

The cold temperature anomaly which is developing in southern Greenland due to melting polar ice is expected to increase over the next few decades.  As this cold anomaly, also known as the North Atlantic Warming Hole (NAWH), becomes more pronounced it will have a significant effect on the Atlantic jet-stream.  At least this is what a team of researchers from the University of Columbia (USA) has predicted following a series of simulation tests.  By taking the evolution of the NAWH into consideration, researchers believe future climactic changes could be better understood.   

Although Sea-surface temperatures (SST) are generally predicted to increase in years to come, there are some very rare regions which will see the inverse effect. This is particularly the case for the North Atlantic Warming Hole which is situated to the south of Greenland.

The development of the NAWH is believed to be due to a slowdown in ocean circulation in which warm waters from the tropics are carried northwards into the North Atlantic ocean.  The increase of fresh water coming from melting Arctic sea ice and polar ice caps into the sub-polar gyre is thought to be the cause if these changes in circulation patterns.

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Linear temperature trend from 1901-2013, in degrees per century. Note the cooling trend in the North Atlantic.  Credits : S. Rahmstorf & al. 2015.

Over the course of 21st century, the cooling pattern of Sea surface temperatures is predicted to increase and become more distinct in this area in terms of internal ocean variability.  In other words as Sea surface temperatures tend to increase elsewhere around the world, the NAWH is expected to become colder.

How is the jet-stream affected?

A team of researchers studied the impact of this anomaly on atmospheric circulation in a paper published in the Journal of Climate. Following the results of three simulation tests, the study’s authors underline the importance of the NAWH in future climate projections due to its affect on the jet stream.

We found that this region of the ocean is a really important place for forcing the jet stream that goes across the North Atlantic Ocean,” stated Melissa Gervais, the leading author of the study.

High altitude, west to east winds also known as the jet stream are influenced by temperature differences between the cold Arctic air and hot air from the tropics.  As a result the potential impact of climate change on the jet-stream is exceedingly important for understanding weather patterns and storms.

According to Melissa Gervais, it is generally understood that the jet stream will see a pole ward shift and an eastward elongation with the effects of climate change. However she noted that, “Right now, it’s sort of a tug of war between impacts of the tropics and impacts of the arctic. So those two things are competing to shift where the jet is located.”

However researchers wanted to see in what ways the North Atlantic Warming Hole could have an affect on the jet stream. Following a series of simulation tests, the researchers noted how the warming hole had an important impact on midlatitude atmospheric circulation changes in the model’s future climate simulations. They noted how the NAWH seemed to be shifting even more to the north and elongating even further. “Instead of just thinking about how the tropics and arctic amplification are influencing the jet, we now also need to think about how this warming hole is going to influence the jet,” explains Melissa Gervais. It should be noted that the European continent is particularly exposed to these dynamic changes to the jet-stream.

Major factor to take into account

Currently there are significant differences between the various CMIP-5 climate projections concerning the Atlantic jet stream’s future evolution – especially in winter. It is clear that many factors need to be considered when predicting the evolution of the Atlantic jet stream. Rising sea surface temperatures certainly play a role however, the results of this study also highlight the impact of the North Atlantic’s cold temperature anomaly.  Unfortunately for the time being relatively little work has been devoted to the subject of the North Atlantic Warming Hole and its effects on the jet stream.

Study: Impacts of the North Atlantic Warming Hole in Future Climate Projections: Mean Atmospheric Circulation and the North Atlantic Jet, Melissa Gervais, Journal of Climate, May 2019.

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