Is Collapse of the Atlantic Ocean Circulation Really Imminent?

Icebergs’ History Reveals Some Clues

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Reprinted with permission from The Conversation.

By YUXIN ZHOU & JERRY McMANUS

When people think about the risks of climate change, the idea of abrupt changes is pretty scary. Movies like “The Day After Tomorrow” feed that fear, with visions of unimaginable storms and populations fleeing to escape rapidly changing temperatures.

While Hollywood clearly takes liberties with the speed and magnitude of disasters, several recent studies have raised real-world alarms that a crucial ocean current that circulates heat to northern countries might shut down this century, with potentially disastrous consequences.

That scenario has happened in the past, most recently more than 16,000 years ago. However, it relies on Greenland shedding a lot of ice into the ocean.

Our new research, published in the journal Science, suggests that while Greenland is indeed losing huge and worrisome volumes of ice right now, that might not continue for long enough to shut down the current on its own. A closer look at evidence from the past shows why.

Blood and water

The Atlantic current system distributes heat and nutrients on a global scale, much like the human circulatory system distributes heat and nutrients around the body.

Warm water from the tropics circulates northward along the U.S. Atlantic coast before crossing the Atlantic. As some of the warm water evaporates and the surface water cools, it becomes saltier and denser. Denser water sinks, and this colder, denser water circulates back south at depth. The variations in heat and salinity fuel the pumping heart of the system.

If the Atlantic circulation system weakened, it could lead to a world of climate chaos.

Ice sheets are made of fresh water, so the rapid release of icebergs into the Atlantic Ocean can lower the ocean’s salinity and slow the pumping heart. If the surface water is no longer able to sink deep and the circulation collapses, dramatic cooling would likely occur across Europe and North America. Both the Amazon rain forest and Africa’s Sahel region would become dryer, and Antarctica’s warming and melting would accelerate, all in a matter of years to decades.

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Today, the Greenland ice sheet is melting rapidly, and some scientists worry that the Atlantic current system may be headed for a climate tipping point this century. But is that worry warranted?

To answer that, we need to look back in time.

A radioactive discovery

In the 1980s, a junior scientist named Hartmut Heinrich and his colleagues extracted a series of deep-sea sediment cores from the ocean floor to study whether nuclear waste could be safely buried in the deep North Atlantic.

Sediment cores contain a history of everything that accumulated on that part of the ocean floor over hundreds of thousands of years. Heinrich found several layers with lots of mineral grains and rock fragments from land.

The sediment grains were too large to have been carried to the middle of the ocean by the wind or ocean currents alone. Heinrich realized they must have been brought there by icebergs, which had picked up the rock and mineral when the icebergs were still part of glaciers on land.

The layers with the most rock and mineral debris, from a time when the icebergs must have come out in force, coincided with severe weakening of the Atlantic current system. Those periods are now known as Heinrich events.

As paleoclimate scientists, we use natural records such as sediment cores to understand the past. By measuring uranium isotopes in the sediments, we were able to determine the deposition rate of sediments dropped by icebergs. The amount of debris allowed us to estimate how much fresh water those icebergs added to the ocean and compare it with today to assess whether history might repeat itself in the near future.

Why a shutdown isn’t likely soon

So, is the Atlantic current system headed for a climate tipping point because of Greenland melting? We think it’s unlikely in the coming decades.

While Greenland is losing huge volumes of ice right now – worryingly comparable to a midrange Heinrich event – the ice loss will likely not continue for long enough to shut down the current on its own.

Icebergs are much more effective at disrupting the current than meltwater from land, in part because icebergs can carry fresh water directly out to the locations where the current sinks. Future warming, however, will force the Greenland ice sheet to recede away from the coast too soon to deliver enough fresh water by iceberg.

The strength of the Atlantic Meridional Overturning Circulation, or AMOC, is projected to decline 24% to 39% by 2100. By then, Greenland’s iceberg formation will be closer to the weakest Heinrich events of the past. Heinrich events, in contrast, lasted 200 years or so.

Instead of icebergs, meltwater pouring into the Atlantic at the island’s edge is projected to become the leading cause of Greenland’s thinning. Meltwater still sends fresh water into the ocean, but it mixes with seawater and tends to move along the coast rather than directly freshening the open ocean as drifting icebergs do.

That doesn’t mean the current isn’t at risk

The future trajectory of the Atlantic current system will likely be determined by a combination of the decelerating but more effective icebergs and the accelerating but less influential surface runoff. That will be compounded by rising ocean surface temperatures that could further slow the current.

So, the Earth’s pumping heart could still be at risk, 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 froze New York City. Based on our research, we may take some comfort in knowing that such a scenario is unlikely in our lifetimes. Nevertheless, robust efforts to stop climate change remain necessary to ensure the protection of future generations.

WE CAN’T CATCH & WE CAN’T RUN

The Planet’s Original FIRE WORKS; Each Strike is 300 Million Volts

JANICE ANNE WHEELER JUN 2

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Long ago, on the North Rim of the Grand Canyon in Arizona (far from my current environment) I watched the mid-day, late November sky darken and was unabashed until I glanced at my companion. Every strand of his straight blonde hair was completely on end, forming a perfect, unearthly orb as he gazed over the abyss, oblivious. That was the first time I felt that kind of power, and while I remember it with awe, we simply sprinted to the Jeep and observed, safely nestled amongst trees and crags on our rubber tires, snapping photos, listening to the thunder, laughing at the lashing, knowing that, however untimely, rain brings precious life to the desert.

Lightning strikes the Little Choptank River, Eastern Shore of Maryland.

Last night on the Chesapeake Bay, out of the corner of my eye I saw the lightning strike, stark white against the blackness of a cloud-covered sky and a moon not yet risen. I turned in that direction and saw a second strike, just north of the first, and felt a sudden temperature drop. The wind shifted and rapidly built. We were docked; no running from this one.

We had hosted a dinner guest and consciously checked the radar to see if we were within Mother Nature’s path of powerful storms that rocked the Midwest last Holiday Weekend. “Fireworks?’ he asked as he climbed down the boarding ladder. He must have sensed the energy, too, or gotten just a glimpse. “No,” I had replied, peering thoughtfully at the sky, but, as I considered those unexpected flashes it dawned on me that lightning is the original, true fire work of our planet, having made a significant contribution to creating life in most scientific theories, if not in the theological ones.

Exponentially more powerful than the Fourth of July celebrations which sometimes reverberate into your very bones, lightning strikes are a surreal release of pent-up energy. Weather.gov tells us that a typical lightning flash contains 300 million volts and 30,000 AMPS. For comparison, household current is 120 Volts and 15 AMPS, and that small amount is strong enough to be fatal if it flows through the (very) conductive human body. A sailing vessel is generally the tallest thing on the water and as a rule lightning is attracted to the closest available point of contact. There you have it. Lightning makes us nervous.

Is it the vulnerability? The outright danger of it? Perhaps it is both. Feeling vulnerable certainly ties closely into our inherent lack of control in regard to Mother Nature and the weather. People often ask if we have encountered big storms, and we have. Here is a recent story about waves and wind: (OVER AND OVER AND OVER ) It’s the lightning, though, that is frightening in its unpredictability. And stunningly beautiful. I become mesmerized as I watch where the last strike was and to see what the next one might bring, only to spot one in a direction I wouldn’t have anticipated.

The majority of the time we won’t be able to outrun, won’t be able to avoid these squalls. They change direction and like tiny little hurricanes the wind on one side blows in the opposite direction of the wind on the other side, so as it passes you have to once again adjust, joust, spar, maneuver, second guess and hope.

Last year, on a northerly course off the coast of Florida, destination Fernandina Beach, we sparred one night, slicing through the narrow space between two rapidly-building, fast-moving cells that joined just behind our transom as we sailed to victory on that run, adrenaline pumping long after we dropped anchor and crept into the shelter of our bed. We’ve seen storms come across the water at astonishing speeds, leaving no chance to even joust before the first whirling gust is upon us. At night you watch the strikes, far off, and hope they don’t change direction but they can, and they do. We receive forecasts from Marine Weather Center (MWXC.com) as a subscription service. While they always warn of the big weather systems, it is the squalls that come with the highest risk, the least consistency, and the most power. I think it is safe to say that weather is an inexact science; no matter how good the forecaster, they can certainly be wrong, just like the rest of us.

When we first moved aboard this ketch-rigged sailing yacht a friend inquired, “Do you have lightning rods?” I replied, “Yes, we do have lightning rods.” After hanging up the phone on that call, I looked at my grew-up-on-the-water husband and chuckled a bit awkwardly. “Yes,” he said to me. “We definitely have two giant lighting rods. One is 65 feet and one is 50 feet.”

A ketch rig is when the main mast is taller than the aft, or mizzen mast. While it may look like lightning rods up there, those are actually VHF antennae.

So, you might ask, is there anything available to deter this particular aspect of Mother Nature’s tendencies? To put yourself at an advantage as you spar out on the open ocean? There are methods and theories going back to the King of Lightning Benjamin Franklin in the 1800’s. These days, Lightning Dissipators are designed to create a negative ion field around the mast, depending on installation. A negative ion controversially creates a ground and more damage can occur with these systems than with nothing at all, according to a veteran Marine Surveyor  and investigator of innumerable lightning strike incidents (full disclosure also my husband Steve Uhthoff). For a much more in-depth examination of this topic, please see this LOOSE CANNON. We take the risks with the rewards.

The first winter we explored the Outislands of the Bahamas (Rum Cay, Conception and beyond) we ran low on fresh water. STEADFAST is designed (thank you Dmitri!) with a fresh water collection system on the roof of her pilot house. During a heavy rain shower it’s impressive how much water can fall from the sky, and without a desalination machine, life on the sea is just like life on the high desert. On a calm passage we encountered a slow-moving thunderhead with what looked like lots of life-saving rain. Full of bright ideas and always up for a challenge, we wiped the salt off the surfaces, unburied and hooked up the extensive network of hoses for the collection system, fired up the Detroit Diesel and headed into what was hopefully a rain shower and not a passing storm cell.

The first spar was so close!! We felt some sprinkles but were outmaneuvered in the end, bone dry and miles off our original course. We had no real destination in mind, no schedule, and were not yet defeated. Soon enough we spotted our next target, seemingly not far away, and in a better direction; we utilized both sails and engine only to watch the dark mass pull away from us once again as we heard the rumble of thunder, saw the fireworks within. Mother Nature was simply sending us a reminder that it’s us that moves slowly. Very slowly. We can’t catch and we can’t run.

We found an anchorage that sheltered us from the wind but not the deluge. Unseen, unpredicted and unheard, the downpour hit us late that very night, the rain collection equipment was stored away, the hatches open, the laundry hung out to dry. The Heavens opened once again, this time right onto the bed. The irony struck me full-on as we bolted on deck stark-naked to shut what needed to be shut and then towel off, laughing, knowing I should have just grabbed the soap…

We learned our lesson and never chased another storm. SPARRING WITH MOTHER NATURE on her terms and winning is elusive enough.

I call these “Holes to Heaven” when the sun’s rays find their way through the clouds, this time in Abaco, Bahamas. It does not make the impending storms less threatening, just more photogenic!

I truly appreciate that you read this story; I have many more to tell you!

Please click the little heart wherever you find it and that send this tale to others like you who may enjoy vivid non-fiction with the ability to make you feel like you were there.

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