Warming Could Push the Atlantic Past a ‘Tipping Point’ This Century

According to a recent analysis, the system of ocean currents that controls the temperature for a large portion of the earth may collapse sooner than previously thought.

When the powerful network of ocean currents that determines the climate surrounding the North Atlantic experienced a significant slowdown previously, it appears to have driven Europe into a deep freeze for more than a millennium.

There were not many people alive to witness it at the time, which was approximately 12,800 years ago. Scientists have been attempting to ascertain whether and when the currents might suffer another great weakening, which would have repercussions for weather patterns throughout a large portion of the planet. However, in recent decades, human-driven warming may be forcing the currents to slow once more.

This week, two scientists from Denmark proposed a daring solution: By the end of the century, we might experience a sharp weakening or perhaps a shutdown of the currents.

Even the researchers were taken aback by the timing of the probable collapse, according to one of them, Susanne Ditlevsen, a professor of statistics at the University of Copenhagen. Although most climatologists concur that the Atlantic circulation will drop this century, there is disagreement about whether it will plateau before 2100.

Because of this, Dr. Ditlevsen said it was also surprising that she and her co-author were able to determine the exact moment a collapse occurred. Dr. Ditlevsen stated that the new findings were sufficient justification for not seeing a shutdown as a hypothetical, distant danger. Scientists are obligated to continue researching and debating the subject, though. It is now, she declared.

The new study, which was released on Tuesday in the journal Nature Communications, adds to a growing body of research that explains how humankind’s continuous emissions of heat-trapping gases could trigger climatic “tipping points,” or quick changes in the environment that are difficult to reverse.

abrupt thawing of the permafrost in the Arctic. The Amazon rain forest is being lost. West Antarctic and Greenland ice sheets melting. Although the precise thresholds at which this might happen are still very uncertain, experts warn that once the earth warms past a certain point, these and other processes could be quickly set into motion.

In a maze of ocean currents known as the Atlantic Meridional Overturning Circulation, or AMOC (pronounced “AY-mock”), scientists have been looking for signs of tipping-point-like change in the Atlantic.

Warm waters from the tropics are carried by these currents via the Gulf Stream, through the southeast of the United States, and then veer northward towards northern Europe. This water sinks to the bottom of the deep ocean and moves back towards the equator as the air farther north absorbs the heat it releases into the atmosphere. The currents have a significant impact on the climate around the Atlantic and beyond because of this sinking effect, or “overturning,” which enables them to transport massive amounts of heat around the earth.

However, the melting of the Greenland ice sheet is adding a lot of fresh water to the North Atlantic, which could be upsetting the equilibrium of heat and salinity that keeps the overturning flowing while people warm the atmosphere. Some experts believe that the appearance of a “cold blob” in the Atlantic south of Greenland in recent years is evidence that the climate system is slowing.

Although scientists are currently assessing their possible size, the repercussions on the climate would be profound should the circulation fall into a significantly weaker condition. The Northern Hemisphere could cool significantly. Sea levels may rise more quickly along North American and European shores. Winter storms may be more frequent in northern Europe, whereas the Sahel region of Africa and the monsoon regions of Asia are likely to get less precipitation.

Ice and sediment core evidence suggests that the Atlantic circulation had sudden stops and starts in the distant past. But since the combination of factors that shapes the currents is so complicated, scientists’ most sophisticated computer models of the global climate have yielded a wide range of projections for how the currents would behave in the upcoming decades.

In his latest study, Dr. Ditlevsen concentrated on a straightforward indicator of the intensity of the Atlantic circulation that is based on sea surface temperatures and is comparable to others that other scientists have employed as proxies. Together with her brother Peter Ditlevsen, a climate scientist at the Niels Bohr Institute at the University of Copenhagen, she carried out the analysis. The statistical indicators that predict changes in the overturning were calculated using data on their proxy measure from 1870 to 2020.

Not only do we observe a rise in these indications, but we also see an increase that is consistent with things nearing a tipping point, according to Peter Ditlevsen.

They then extrapolated from these trends using the mathematical characteristics of a system resembling a tipping point. They concluded that the Atlantic circulation could collapse in the middle of the century, though it could happen as early as 2025 or as late as 2095.

They made no exact predictions about how much greenhouse gas emissions will increase in the coming century in their analysis. Only the unchanging rate of the factors causing an AMOC collapse—basically, the continuation of the rise in atmospheric carbon dioxide concentrations since the Industrial Revolution—was assumed.

Given how challenging it has been to anticipate when we would cross a tipping point using computer models of the global climate, numerous experts who study the topic praised the new analysis in interviews for employing a different technique. However, they expressed scepticism over several of its methodologies and claimed that additional study has to be done in order to more precisely pinpoint the timing.

Physical oceanographer Susan Lozier of Georgia Tech argued that sea-surface temperatures in the North Atlantic near Greenland weren’t always affected by variations in the overturning, making them a suspect proxy for estimating those variations. She cited a research from the previous year that demonstrated changes in wind and atmospheric patterns could account for a large portion of the cold blob’s growth.

Currently, sensors draped over the Atlantic are being used by scientists to measure the overturning directly. Among these measuring initiatives is one in which Dr. Lozier is active. The goal is to enhance predictions of future changes and gain a better understanding of what’s causing the changes beneath the waves.

However, the initiatives didn’t start gathering data until 2004 at the earliest, which isn’t long enough to make definite long-term predictions. Dr. Lozier said that it is “extremely difficult to look at a short record for the ocean overturning and predict what it will do over 30, 40, or 50 years.”

The older temperature records that Dr. Ditlevsen and Dr. Ditlevsen used to compute their proxy raised concerns from Levke Caesar, a postdoctoral researcher investigating the overturning at the University of Bremen in Germany. Without appropriate changes, she warned that these records from the late 19th and early 20th centuries might not be trustworthy enough to be utilised for fine-toothed statistical analysis.

Nevertheless, the new study urgently underlined the need to continue gathering information on the shifting ocean currents, according to Dr. Caesar. There is probably something unusual going on, she remarked, adding that something is happening. if not for us humans, “something that wouldn’t have happened.”

According to Hali Kilbourne, an associate research professor at the University of Maryland Centre for Environmental Science, the fact that scientists are unsure exactly when an AMOC collapse would occur shouldn’t be used as an excuse for not lowering greenhouse gas emissions to try to prevent it.

The possibility that we have already fallen off a cliff and are unaware of it is extremely real, according to Dr. Kilbourne. Sincerely, I worry that it will be far too late to take action by the time any of this becomes established science.

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