An influential current system in the Atlantic Ocean, which plays a vital role in redistributing heat throughout our planet’s climate system, is now moving slower than in at least 1,600 years. This is the conclusion of a new study published in the journal Nature Geoscience from some of the world’s leading experts in this field.
Scientists believe that part of this slowdown is directly related to our warming climate, as melting ice changes the balance in the northern waters. Its impact can be seen in storms, heat waves and rising sea levels. And it raises concerns that if people are not able to limit warming, the system could eventually reach a tipping point, throwing global climate patterns into disarray.
The flow of the Gulf along the east coast of the United States is an integral part of this system, known as the South Atlantic Overturning Circulation or AMOC. He was famous in the 2004 film “The Day After Tomorrow”, in which the ocean current suddenly stops, causing huge deadly storms that swirl around the globe, like an overloaded tornado in Los Angeles and a wall of water breaking in New York. York.
As with many SF movies, the plot is based on a real concept, but the impact is taken to a dramatic extreme. Fortunately, a sudden power outage is not expected soon – if ever. Even if the current were to stop in the end – and this is hotly debated – the result would not be instantaneous storms greater than life, but in years and decades the impact would certainly be devastating for our planet.
Recent research has shown that traffic has slowed by at least 15% since 1950. Scientists in the new study say the current is weakening “unprecedented in the last millennium.”
Because everything is connected, the slowdown is undoubtedly already having an impact on Earth’s systems, and by the end of the century, it is estimated that circulation could slow down by 34% to 45% if we continue to warm the planet. Scientists fear that this type of slowdown would put us dangerously close to peak points.
The importance of the global ocean conveyor belt
Because the equator receives much more direct light than colder poles, heat accumulates in the tropics. In an effort to reach equilibrium, the Earth sends this heat north from the tropics and sends cold south from the poles. This is why the wind blows and storms form.
Most of that heat is redistributed by the atmosphere. But the rest is moved more slowly by the oceans in what is called the Global Ocean Conveyor Belt – a global system of currents that connects the world’s oceans, moving in all different directions horizontally and vertically.
NOAA
Over the years of scientific research it has become clear that the Atlantic portion of the conveyor belt – AMOC – is the engine that drives its operation. Move water 100 times the flow of the Amazon River. Here’s how it works.
A narrow band of warm, salty water in the tropics near Florida, called the Gulf of Gulf, is being transported north, near the surface, into the North Atlantic. When it reaches the Greenland region, it cools enough to become denser and heavier than the surrounding waters, at which point it sinks. The cold water is then transported south into deep water currents.
Through proxy recordings, such as ocean sediment cores, that allow scientists to reconstruct the distant past that goes back millions of years, scientists know that this current has the ability to slow down and stop, and when that happens, the climate in the northern hemisphere can change rapidly.
An important mechanism over the centuries, which acts as a kind of lever that controls the speed of AMOC, is the melting of ice and the resulting influx of fresh water into the North Atlantic. This is because fresh water is less salty and therefore less dense than sea water and does not sink as easily. Too much fresh water means that the conveyor belt loses its diving part of the engine and thus loses its momentum.
That’s what scientists think is happening now like ice in the Arctic, in places like Greenland, it melts at an accelerated pace due to man-made climate change.
Central climate
Recently, scientists have noticed a cold spot, also known as the North Atlantic heating hole, in a patch of the North Atlantic in southern Greenland – one of the only places that actually cools on the planet.
The fact that climate models have predicted this provides more evidence that it is indicative of excessive melting ice in Greenland, more rainfall and a consequence of slowing heat transport north from the tropics.
GODMOTHER
To determine how unprecedented the recent slowdown in AMOC is, the research team compiled proxy data taken primarily from nature’s archives, such as ocean sediments and ice cores, dating back more than 1,000 years. This helped them reconstruct the history of the AMOC flow.
The team used a combination of three different types of data to obtain information about the history of ocean currents: Atlantic Ocean temperature patterns, groundwater properties, and the size of deep sediment granules dating back 1,600 years.
Although each individual piece of proxy data is not a perfect representation of the evolution of AMOC, their combination revealed a robust picture of inverted circulation, says lead author Dr. Levke Caesar, a climate physicist at Maynooth University in Ireland. .
“The results of the study suggest that it was relatively stable until the end of the 19th century,” explains Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany.
The first significant change in their ocean records occurred in the mid-1800s, after a period of well-known regional cooling called the Little Ice Age, which stretched from the 1400s to the 1800s. During this time, colder temperatures froze. frequently rivers in Europe and destroyed crops.
“With the end of the Little Ice Age around 1850, ocean currents began to decline, following a second, more drastic decline, beginning in the mid-20th century,” Rahmstorf said. The second decline in recent decades has probably been due to global warming caused by burning and emissions of fossil fuels.
Nine of the 11 data sets used in the study showed that the weakening of AMOC in the twentieth century is statistically significant, which provides evidence that the slowdown is unprecedented in the modern era.
Impact on storms, heat waves and sea level rise
Caesar says this is already reverberating in the climate system on both sides of the Atlantic. “As the current slows, more water can accumulate on the east coast of the United States, leading to improved sea level rise. [in places like New York and Boston], “she explained.
On the other side of the Atlantic, in Europe, evidence shows that there are impacts on weather patterns, such as traces of storms coming out of the Atlantic, as well as heat waves.
“Specifically, the European heat wave in the summer of 2015 was linked to the record cold in the North Atlantic that year – this seemingly paradoxical effect occurs because a cold North Atlantic promotes a model of air pressure that channels warm air from the south to Europe, “she said.
According to Caesar, these impacts will continue to worsen as the Earth continues to warm and AMOC slows further, with more extreme weather events such as a change in the runway of winter storms coming out of the Atlantic and potentially more severe storms. intense.
CBS News asked Caesar the million-dollar question: If or when AMOC could reach a tipping point that would lead to a complete shutdown? She replied: “Well, the problem is that we still don’t know how many degrees of global warming the AMOC should reach. But the slower it slows down, the more likely we are to do it.”
Moreover, she explained, “Tipping does not mean that this happens instantly, but rather that, due to feedback mechanisms, the continuous deceleration cannot be stopped once the tipping point has been passed, even if we have managed to we are reducing global temperatures again. ”
Caesar believes that if we stay below 2 degrees Celsius of global warming, it seems unlikely that the AMOC will decline, but if we reach 3 or 4 degrees of warming, the chances of growth will increase. Staying below 2 degrees Celsius (3.6 degrees Fahrenheit) is a goal of the Paris Agreement, which The United States has just reunited.
If the tipping point is crossed and the AMOC stops, it is likely that the northern hemisphere will cool due to a significant decrease in tropical heat being pushed north. But beyond that, Caesar says that science does not yet know exactly what would happen. “That’s part of the risk.”
But humans have a role to play in all of this, and the decisions we make now about how quickly we move from fossil fuels will determine the outcome.
“Whether or not we pass by the end of this century depends on the amount of heating, ie the amount of greenhouse gases emitted into the atmosphere,” explains Caesar.