Is the Atlantic Ocean Circulation Collapse Coming? The History of Icebergs Offers Some Hints

The thought of sudden, drastic shifts terrifies individuals when they consider the threats associated with climate change. Films like "The Day After Tomorrow," which depict unspeakable storms and depict people escaping quickly shifting temperatures, stoke people's anxiety.

Even though Hollywood often exaggerates the severity and speed of disasters, several recent studies have raised concerns about the possibility that this century, a vital ocean current that transfers heat to northern countries could stop, with potentially fatal results.

More than 16,000 years ago was the most recent time such a situation occurred. But it depends on Greenland releasing a significant amount of ice into the sea.

Our recent study, which was published in the journal Science, indicates that although Greenland is currently losing alarmingly large amounts of ice, this may not last long enough to stop the current on its own. A thorough examination of historical data demonstrates why.

Water and blood

Similar to how the human circulatory system distributes heat and nutrition throughout the body, the Atlantic current system disperses heat and nutrients globally.

Before crossing the Atlantic, warm water from the tropics moves northward along the Atlantic coast of the United States. The surface water gets denser and saltier as it cools and part of the warm water evaporates. Colder, denser water flows back south at depth as denser water sinks. The pumping mechanism of the system is powered by changes in salinity and temperature.

Climate anarchy could result from a weakening of the Atlantic circulation system.

Since fresh water makes up ice sheets, the sudden release of icebergs into the Atlantic can reduce the salinity of the water and slow the heartbeat. Significant cooling is probably going to happen throughout Europe and North America if surface water is unable to descend deeply and the circulation breaks down.

In a couple of years or decades, the Amazon rain forest and the Sahel region of Africa would both become drier, while Antarctica's warming and melting would quicken.

The Greenland ice sheet is melting quickly right now, and some experts are concerned that this century may mark a tipping point in the climate for the Atlantic current system. Is that concern justified, though?

We must go back in time to find the solution to it.

Discovery of radioactivity

A group of scientists led by a junior scientist called Hartmut Heinrich collected several deep-sea sediment cores from the ocean floor in the 1980s to investigate the possibility of properly burying nuclear waste in the deep North Atlantic.

The history of everything that gathered over hundreds of thousands of years on that portion of the ocean floor is preserved in sediment cores. Heinrich discovered multiple layers including numerous mineral grains and pieces of land-based rock.

The size of the silt grains prevented the wind or ocean currents from carrying them to the middle of the ocean. Heinrich concluded that the icebergs must have carried the rock and minerals there when they were still a part of the glaciers.

The layers that included the greatest amount of rock and mineral debris were formed during a period when the Atlantic current system was severely weakened. We now refer to those times as Heinrich occurrences.

To comprehend the past, paleoclimate experts examine natural archives like sediment cores. We measured the uranium isotopes in the sediments to find out how quickly icebergs deposited sediments. Because there was so much debris, we were able to calculate the amount of freshwater that those icebergs added to the ocean and compare it to the current state of the ocean to determine whether history would repeat itself anytime soon.

Why a closure is unlikely to occur soon

So, is the melting of Greenland causing the Atlantic current system to approach a tipping point in terms of climate? We believe that in the upcoming decades, it is unlikely.

Even while Greenland is currently shedding enormous amounts of ice, which is concerningly similar to a moderate Heinrich event, the ice loss is probably not going to last long enough to stop the current on its own.

Because icebergs can transport fresh water directly to the places where the current lowers, they are far more effective at blocking the current than meltwater from the land. However, as a result of future warming, the Greenland ice sheet will have to retreat from the shore too soon to allow icebergs to carry enough fresh water.

By 2100, it is predicted that the Atlantic Meridional Overturning Circulation, or AMOC, would be weaker by 24% to 39%. At that point, the iceberg development in Greenland will resemble the weakest Heinrich occurrences in history. In contrast, the Heinrich events lasted roughly 200 years.

Meltwater flowing into the Atlantic along the island's edge is expected to become the main factor contributing to Greenland's thinning, rather than icebergs. Though it does not directly replenish the open ocean like floating icebergs do, meltwater nevertheless contributes to the ocean's replenishment because it combines with saltwater and flows along the coast.

That does not absolve the current risk.

The Atlantic current system's future course will probably be dictated by a mix of the slowing but The Earth's pumping heart may still be in danger, but history suggests that the risk is not as imminent as some people fear. In "The Day After Tomorrow," a slowdown of the Atlantic current system caused New York City to freeze. Based on our research, we may take some solace in the knowledge that such a scenario is unlikely in our lifetimes. Nevertheless, strong efforts to stop climate change remain important to ensure the protection of future generations.