Gulf Stream is certainly weakening, as confirmed by a new study. Flow of warm water through the Florida Strait has slowed by 4% over the past four decades, with significant implications for the global climate.

The ocean current originates near Florida and travels as a band of warm water along the eastern coast of the United States and Canada before crossing the Atlantic towards Europe. Heat it carries is essential for maintaining temperate conditions and regulating sea levels.

Thermohaline Circulation

Researchers in a study published on September 25 in the journal Geophysical Research Letters (ref.) raise the alarm. “This is the strongest evidence we have of the weakening of this climatically significant ocean current” said Christopher Piecuch, a physical oceanographer at the Woods Hole Oceanographic Institution in Massachusetts.

The Gulf Stream is just a small component of the thermohaline circulation. This current is a global ocean conveyor belt that transports oxygen, nutrients, carbon, and heat around the planet. The water’s movement contributes to controlling sea level and hurricane activity simultaneously.

Originating from the Caribbean, the Gulf Stream carries warmer, saltier, denser southern waters northward to cool and sink in the North Atlantic. After sinking deep beneath the ocean and releasing its heat into the atmosphere, the water moves slowly southward, where it warms again, and the cycle repeats. This process is vital for maintaining temperature and sea level. For example, along the eastern coast of the United States, the water is kept up to 1.5 meters lower than offshore waters (ref.).

Correlation with Climate Change

As the Earth‘s climate warms, a massive influx of freshwater and cold water (ref.) from melting ice is pouring into the oceans. That’s why, according to scientists, the Gulf Stream is weakening. However, due to the size and complexity of the system, it is very difficult to prove.

To find definitive evidence that the flow is slowing down, scientists have analyzed 40 years of data from three separate sources submarine cables, satellite altimetry, and on-site observations. Their statistical analysis revealed that the current has slowed by 4%, with only a 1% chance that the measurement was a stroke of luck caused by random fluctuations.

A 4% shift may seem like a tiny change, but “the concern is that it’s just a slow start” said Helen Czerski, an oceanographer at University College London (UCL). “It’s like in the early days of COVID. People were saying, Oh, there are only 60 cases. We don’t care” she added. “There are only 60 cases, yes, but yesterday it was 30, and the day before it was 15. If you just think a week ahead, we have a problem”.

To find definitive evidence that climate change is the culprit, scientists will need to distinguish the differences between the natural variability of oceanic systems and the impact produced by global warming. This is a challenging task given the relatively short time humans have directly measured climate change and oceanic flows in detail.

Martina De Luca
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