Gulf Stream is weakest it's been in more than 1,000 years, study says

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This Tuesday, Nov. 10, 2020, satellite image made available by NOAA shows Tropical Storm Eta at 10:40 a.m. EST in the Gulf of Mexico, Theta, right, and a tropical wave to the south that became Tropical Storm Iota. An overheating world obliterated weather records in 2020 - an extreme year for hurricanes, wildfires, heat waves, floods, droughts and ice melt - the United Nations' weather agency reported Wednesday, Dec. 2, 2020. (NOAA via AP)

A group of scientists from Europe presented new research this week claiming that the Gulf Stream is weaker now than it's been at any point over the last 1,000 years. The Gulf Stream is an Atlantic Ocean current that plays a largely hidden role in shaping weather patterns in the United States. Much has been researched and learned about the influential current over the past 500 years, particularly due to the expertise of one of America's Founding Fathers, Benjamin Franklin.

But in recent decades, a shift in the Gulf Stream's circulation has become weaker than any other time over the last millennium, according to a recently published study by scientists from Ireland, Britain and Germany. The weakening of the Gulf Stream, formally known as the Atlantic Meridional Overturning Circulation (AMOC), can be mostly pinned to one catalyst, the researchers said: human-caused climate change.

The Gulf Stream current moves a massive amount of water across the Atlantic Ocean. According to Stefan Rahmstorf, one of the study's authors, it moves nearly 20 million cubic meters of water per second, acting like a giant conveyor belt.

How strong of a current is that? "Almost a hundred times the Amazon flow," he told the Potsdam Institute.

The Gulf Stream location in the Global Real-Time Ocean Forecast System model (RTOFS) from 2016. (Image via NOAA)

The main function of the Gulf Stream is to redistribute heat on Earth by way of the ocean current. The ocean circulatory system plays a crucial role in many weather patterns around the world, particularly along the U.S. East Coast.

Rahmstorf said that his team's research was groundbreaking for being able to combine previous bits of research to piece together a 1,600-year-old picture of the AMOC evolution.

"The study results suggest that it has been relatively stable until the late 19th century," he said. "With the end of the little ice age in about 1850, the ocean currents began to decline, with a second, more drastic decline following since the mid-20th century."

An original mapping of the Gulf Stream from Timothy Folger and Benjamin Franklin from 1768. (Image via Library of Congress)

So what are the implications of this decline in the ocean currents? AccuWeather Senior Meteorologist Bob Smerbeck said it could plausibly lead to rising sea levels if water levels are warmed this year. However, Smerbeck added that it is tricky to know just how warm the waters could get.

Previously, studies have shown that rising water temperatures and higher sea levels can lead to more extreme weather events such as stronger tropical storms, a higher likelihood for extreme heat waves or a decrease in summer rainfall.

However, other researchers have also come out with contrasting data, suggesting that the Gulf Stream hasn't actually declined over the past 30 years. Using a different data modeling system, researchers from the United Kingdom and Ireland pieced together data from climate models that they said in a study published earlier this month showed "no overall AMOC decline."

"Our results reinforce that adequately capturing changes to the deep circulation is key to detecting any anthropogenic climate-change-related AMOC decline," the authors write in their study, which was written just days before Rahmstorf's team published its research on the topic.

Smerbeck, who has been a meteorologist at AccuWeather for nearly 25 years, urged caution in how to interpret the new research claims.

"One possible repercussion discussed in article 1 [the first study mentioned above] about warming waters along the east coast from an AMOC slowdown could lead to rising sea levels due to thermal expansion of the seawater. This seems plausible," Smerbeck said. But, he added that the amount of seawater rise would depend on how warm that waters could get and he wasn't ready to speculate on that.

This undated engraving shows the scene on July 4, 1776, when the Declaration of Independence was approved by the Continental Congress in Philadelphia, Pa. The document, drafted by Thomas Jefferson, Benjamin Franklin, John Adams, Philip Livingston and Roger Sherman, announces the separation of 13 North American British colonies from Great Britain. The formal signing by 56 members of Congress began on Aug. 2. (AP Photo)

How was the Gulf Stream as we know it today discovered? Well, the discovery was fueled by a need for increased efficiency with the mail service and was inspired by the empiricism of whalers.

In 1768, Benjamin Franklin was working in London as deputy postmaster, according to The Smithsonian Magazine, responsible for overseeing the arrival of mail to and from the American colonies. His cousin, Timothy Folger, worked as a captain of a merchant ship at that same time.

One day, Franklin asked Folger why his merchant ships arrived at the colonies much faster than Franklin's mail ships made it back to England. Folger explained to his cousin that merchant captains followed the advice of whalers, who followed a "warm, strong current" to track and kill whales.

While Franklin said mail captains were too prideful to follow the advice of "simple American fishermen," sailing against the current was costing precious time, according to author Laura Bliss.

So Folger sketched out a general location of the current for Franklin, dubbing it the "Gulph Stream." However, Franklin's mail carriers refused to follow the directions.

A chart of the Gulf Stream, published in 1786 in the Transactions of the American Philosophical Society. (Image via Library of Congress, Geography and Map Division)

But when Franklin switched allegiances to the burgeoning United States during the Revolutionary War, he mapped out a more precise route of the AMOC and gave it to French allies, providing them a key advantage in the battle of European Maritimers, according to The Smithsonian. The combination of Folger's whaling knowledge and Franklin's mapping would become crucial in later understanding the importance of the current, even if they originally were just trying to figure out how to deliver mail faster.

While knowledge of the AMOC may only go back a few hundred years, Smerbeck said the dating of the currents can be done in a variety of different ways. Direct measurements with deep-ocean instruments only go back to 2004, he said, but other methods can help piece together the puzzle, such as analysis of coral and historical data from ship logs.

"Tree rings can tell how wet or dry the nearby land climate was in the past, which can be linked to sea surface temperatures," Smerbeck explained. "Ice cores can pretty much tell the same thing as well as how warm or cold it was in the past," he said. "Ocean sediments can show if there were high or low runoff periods from nearby precipitation over land, which could be linked to how warm or cold sea surface temperatures were in the past." Researchers have used all of these clues to inform the understanding, which stretches back more than a millennium, they've developed of the Gulf Stream.

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