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A catastrophe like in The Day After Tomorrow: the currents of the world's oceans are slowing down, and this threatens with strong hurricanes

The influential system of currents in the Atlantic Ocean, which plays a vital role in the redistribution of heat throughout the entire climate system of our planet, is now moving more slowly than in the past 1600 years. This is the conclusion of a new study published in the journal Nature Geoscience by some of the world's leading experts in the field. The edition told in more detail CBS News.

Photo: Shutterstock

Scientists believe that part of this slowdown is directly related to climate warming, as melting ice changes the balance in northern waters. Its effects can be seen in storms, heat waves and rising sea levels. And this heightens fears that if humans fail to limit warming, the situation could eventually reach a tipping point, disrupting global climate models.

The Gulf Stream along the east coast of the United States is an integral part of the climate system known as the Atlantic meridional overturning circulation (AMOC). She became famous for the 2004 film The Day After Tomorrow, in which the ocean currents suddenly stop and cause huge deadly storms around the globe, such as the super tornado in Los Angeles and the water wall that covered New York.

As with many sci-fi films, the plot is based on a real concept, but the consequences are pushed to the dramatic extreme. Fortunately, the tide is not expected to stop abruptly anytime soon, if ever. Even if the current eventually stops, and this is actively discussed, the result will not be instant storms that exceed the scale of life, but after years and decades, their impact will certainly be devastating to the planet.

Recent studies have shown that water circulation has slowed by at least 1950% since 15. Scientists in the new study say the weakening of the current is "unprecedented in the last millennium."

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Since everything is interconnected, the slowdown is undoubtedly already having an effect on the Earth, and it is estimated that by the end of the century, circulation could slow by 34-45% if humanity continues to heat the planet. Scientists fear that this slowdown will bring us dangerously close to tipping points.

The importance of global ocean currents

Because there is much more direct sunlight at the equator than at the colder poles, heat builds up in the tropics. In an effort to achieve balance, the Earth sends this heat north from the tropics and - cold south from the poles. This is what makes the wind blow and form storms.

Most of this heat is redistributed by the atmosphere. But the rest moves more slowly by the oceans in the so-called Global Oceanic Conveyor Belt - a worldwide system of currents that connect the world's oceans moving in all different directions horizontally and vertically.

Over the years of scientific research, it has become clear that the Atlantic section of the conveyor belt - the AMOC - is the engine that drives it. It moves water 100 times faster than the Amazon River. Here's how it works: A narrow strip of warm salt water in the tropics near Florida, called the Gulf Stream, is swept north 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. Then this cold water is carried south by deep currents.

Through indirect methods such as ocean sediment cores, which allow scientists to reconstruct the distant past, stretching back millions of years, scientists know that this flow can slow down and stop. And when that happens, the climate in the Northern Hemisphere can change quickly.

One important mechanism over the centuries that acts as a kind of lever that controls the speed of AMOC is the melting of glacial ice and, as a result, the influx of fresh water into the North Atlantic. This is because fresh water is less salty, therefore less dense than sea water, and does not sink as quickly. Too much fresh water means the conveyor belt is losing the sinking part of its engine and thus losing momentum.

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This is what scientists believe is happening now as ice in the Arctic, in places like Greenland, is melting at an accelerated rate due to anthropogenic climate change.

Scientists recently noticed a cold blob, also known as the North Atlantic Warming Hole, in a stretch of the North Atlantic around southern Greenland, one of the few places on the planet that is actually cooling.

The fact that climate models predicted this provides more evidence that this is evidence of excess ice melting in Greenland, increased rainfall and, as a consequence, slower heat transport northward from the tropics.

To establish how unprecedented the AMOC slowdown is, the research team collected proxy data, drawn primarily from natural archives such as ocean sediments and ice cores, over 1000 years. This helped them reconstruct the history of AMOC.

The team used a combination of three different types of data to obtain information about the history of ocean currents: temperature regimes in the Atlantic Ocean, properties of groundwater masses, and grain sizes of deep-sea sediments, which are 1600 years old.

While each individual piece of proxy data is not a perfect representation of the evolution of AMOC, the combination showed a robust pattern of circulation, says lead author Dr. Levke Zeisar, a climatologist at Maynooth University in Ireland.

“The results of the study show that the current was relatively stable until the end of the XNUMXth century,” explains Stefan Ramstorf of the Potsdam Institute for Climate Impact Research in Germany.

The first significant change in their records of ocean circulation occurred in the mid-1800s, following a well-known cooling period in the region called the Little Ice Age, which lasted from the 1400s to the 1800s. During this time, colder temperatures often froze rivers across Europe and destroyed crops.

“With the end of the Little Ice Age around 1850, ocean currents began to decline, and from the middle of the twentieth century a second, sharper decline followed,” Ramstorf said. This second decline in decades was likely due to global warming from combustion and emissions of pollutants from fossil fuels.

Nine of the 11 datasets used in the study showed that the weakening of AMOC in the XNUMXth century is statistically significant, indicating an unprecedented slowdown in growth in the modern era.

Impacts on storms, heat waves and sea level rise

Zeisar says this is already affecting the climate on both sides of the Atlantic.

“As the current slows down on the east coast of the United States, more water can accumulate, leading to increased sea level rise in places like New York and Boston,” she explained.

Across the Atlantic, in Europe, data show that there are impacts on weather conditions such as storms from the Atlantic Ocean as well as heatwaves.

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“In particular, the European heatwave in the summer of 2015 was associated with a record cold in the North Atlantic Ocean that year - this seemingly paradoxical effect arises from the fact that the cold North Atlantic Ocean contributes to the formation of air pressure, which directs warm air from the south to Europe ”, - commented Zeisar.

These impacts are likely to further worsen, she said, as the Earth continues to heat up and the AMOC slows down even further with more extreme weather events such as a reversal in the trajectory of a winter storm emanating from the Atlantic and potentially more severe storms.

“The problem is, we don't yet know at what degree of global warming the AMOC tipping point will come. But the more it slows down, the more likely it is that the flow will stop, ”she said.

In addition, the climatological physicist explained: "Rather, due to feedback mechanisms, the ongoing deceleration cannot be stopped after the tipping point is overcome, even if we manage to bring global temperatures back down."

If humanity can keep global warming at 2 degrees Celsius, then it is unlikely that AMOC will stop, but if we reach 3 or 4 degrees of warming, the chances will increase. Keeping temperatures below 2 degrees Celsius (3,6 degrees Fahrenheit) is the goal of the Paris Agreement, which the US recently rejoined.

If the tipping point is overcome and the AMOC comes to a standstill, it is likely that the Northern Hemisphere will cool off due to a significant decrease in tropical heat being pushed northward. But Zeisar says science doesn't yet know exactly what will happen.

While humans do have some leeway in all of this, the decisions we make now in terms of how quickly we get rid of fossil fuels will determine the outcome.

“Whether or not we pass the tipping point towards the end of this century depends on the degree of warming, that is, the amount of greenhouse gases emitted into the atmosphere,” explains Zeisar.

Hurricane season

The resulting state of La Niña is predicted to disappear in the next few months. La Niña could affect hurricane season, and what will its absence do, the publication said MLive.

La Niña is a time when the surface of the tropical Pacific Ocean becomes colder than usual. La Niña can affect the entire flow of tropical winds and storm currents. During La Niña, a gentle Atlantic wind blows stronger and more stable from east to west. This wind flow situation helps Atlantic hurricanes travel west across the Atlantic towards the United States. East-to-west wind flow means less wind shear for hurricanes and helps keep them from breaking apart.

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In one of its most recent hurricane season forecast updates, the National Oceanic and Atmospheric Administration (NOAA) said: “La Niña could help increase hurricane activity in the Atlantic, thereby mitigating wind shear over the Caribbean and the tropical Atlantic, allowing storms to develop. and grow, ”said Mike Halpert, deputy director of the NOAA Climate Prediction Center. “La Niña's development potential has been factored into our updated Atlantic hurricane season forecast.”

La Niña is now projected to disappear this spring. This means that the major factor that hurricanes bring to the United States will not be present in this coming hurricane season.

The surface water temperature graph shows that the water temperature has decreased over the past few months.

That is, some of the forecasting models even translate La Niña into an El Niño state.

It seemed like the 2020 hurricane season would never end. Without La Niña, tropical weather activity may be less during the 2021 hurricane season. Of course, this does not mean that there can be no hurricanes - there will probably be fewer of them.

And if the ocean really went into an El Niño state, the hurricanes in the Atlantic would be even harder.

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