Study predicts the Atlantic current may collapse. What it means for climate, rising sea

Will Cape Cod end up under water if a major system of currents in the North Atlantic stop working together to move around water and influence weather patterns and sea level rise?

Christopher Piecuch, an associate scientist in the oceanography department at the Woods Hole Oceanographic Institution, doesn't think so, but it would certainly accelerate sea level rise here where some areas would disappear, lead to faster beach erosion, and bring more intense weather.

A new study published Tuesday suggests that the Atlantic Meridional Overturning Circulation — a large system of ocean currents that conveys warm water from the tropics to the North Atlantic and brings cold water southward —– could collapse anytime from 2025 onward, most likely by mid century, because of human-caused climate change.

Piecuch described the system as "this ribbon of currents" that collectively work together to move around warm and cold water, as well as nutrients, not only in a continuous north to south circulation but also a vertical circulation from the ocean floor to the surface.

"The Overturning Circulation is one of a few really key tipping points in the climate system that we're really interested in," he said. "This is a strong control in our climate and we have real strong evidence of its importance."

Confusion exists between the Overturning Circulation, Gulf Stream

He said people often confuse the Overturning Circulation with the Gulf Stream because "it (the Gulf Stream) is a very well-defined feature that's known to us, a current we've known about for centuries that's an important player in the ocean and weather."

The Gulf Stream is only part of the Overturning Circulation, and contrary to some reports in the media, he stressed, "the Gulf Stream is not going to collapse."

As for whether the Overturning Circulation is headed toward a collapse, Piecuch said the jury is still out. The new study, he said, is not necessarily a "silver bullet," even though it predicts a collapse with 95% certainty between 2025 and 2095.

Concerns exist, though

But that's not to say it's not concerning and shouldn't be taken into account, he said.

"This study is sort of one more witness that's been brought to the stand," he said, noting it's asked the same question many scientists have been asking and studying which is: "what will be the future of the Overturning?"

Based on geological and paleological evidence, Piecuch said, "we know there have been times in the past when the Overturning Circulation has weakened." And studies that have been done to date all point to a conclusion that the current is probably, at the very least, weakening at a faster rate than would have been expected naturally because of human-escalated climate change.

"It is of interest to us to understand what trajectory the Overturning is taking," he said. "We always want to bring different vantage points in. (This study) provides a very new angle on the problem. It does, in some regards, tell us what we already know — that there will be a further weakening of the Overturning Circulation."

More studies telling the same story need to be assembled, though, before there can be any consensus on the study's findings.

Significant changes to the current would bring weather changes

Certainly the effects from a collapse of the current would be stronger than what would come with a weakening, he said.

The current has influence on precipitation patterns and weather, Piecuch explained, so significant changes to how it's working can result in more significant rain events in some places with the result of flooding, or less precipitation in other areas and droughts, warmer temperatures in the northwest Atlantic region, and stronger storms. The intensity would be greater if the current was to collapse.

And then there is sea level rise.

"There are a lot of studies that link the strength of the Overturning Circulation with sea level rise," he said. "When the Overturning Circulation weakens, you have a rise in sea level along the East Coast."

This is problematic because the East Coast is already experiencing sea level rise that's faster than the global average, he pointed out, so a weakening or collapse of the current would result in added sea level rise that's specific to the East Coast.

In turn, this would result in more rapid coastal erosion.

Concerns about the current's effects on dispersing heat in the ocean

There are also concerns about the current's involvement with dispersing heat in the ocean.

"When you weaken the Overturning Current, the impact in terms of ocean temperatures is you see a distinct pattern of ocean temperature changes," Piecuch said.

A weakening of the current would lead to some cooling in the North Atlantic, but "at the same time you get warming in the Gulf of Maine and Atlantic Canada," he said. The overall effect is enhanced warming on top of what is already being observed here, as the Gulf of Maine is recognized as one of the fastest warming water bodies on the planet.

Dramatic shifts in marine populations could occur

As a result, more dramatic shifts in marine populations would be expected, which is a concern for fisheries in terms of "where things are," he noted.

Warming also provides fuel for hurricanes. Piecuch pointed at Hurricane Katrina as an example of a storm that gained strength from warm water as it passed over the Gulf of Mexico and brought devastating consequences to states on the Gulf.

Cape Cod has generally been spared from direct hits by hurricanes coming up the coast, but a weakening or collapse of the current would be expected to bring more frequent and more intense storms.

Inundation on parts of Cape Cod could occur

While analysis would need to be done to determine what percentage of Cape Cod could end up under water as a result of changes to the current, some areas would certainly be expected to be inundated. Local studies by the Waquoit Bay National Estuarine Research Reserve have predicted up to a 90% chance of sea level rise between eight inches and 6.6 feet by 2100 — that's without taking into account a collapse of the Overturning Circulation.

"In principal, you worry about erosion of beaches," Piecuch said.

The Cape also has fragile salt marshes. While they have resilience built into them where they can, "within a certain envelope," build up silt and absorb sea level rise, the question is "can the salt marshes keep pace with sea level rise?"

"We're concerned about the viability of our coastal ecosystems," he said.

'We're not powerless here'

The situation is certainly concerning, he said, but added he can't help but get frustrated with the tendency for some people to be fatalistic, shrug it off as something that they can't do anything about, and go about business as usual.

"We're not powerless here," he emphasized. "If you look at all these projections of future climate change there's a really big difference between a world where you reduce emissions globally and act locally" and a world where nothing is done.

Fortunately, that attitude is overshadowed here, where people have already started dealing with issues related to climate change, have accepted that it is happening and are taking action, he said.

"There's a lot that coastal communities here on the Cape and the Islands are doing," he said.

Cape Cod climate group reacts to study

The latest study on the Overturning has rung alarm bells for the Cape Cod Climate Change Collaborative.

"The report released this week indicates that some of the most devastating impacts of climate change, including changes in the ocean currents, could possibly occur earlier, even far earlier, than scientists had previously estimated," said Janet Williams, vice president of the collaborative.

The findings, according to the organization, "underscore the increasingly urgent need for immediate action to reduce global greenhouse gas emissions to try to avoid some of these impacts, and to prepare for what seems likely to be coming."

The news only adds more steam to the organization's efforts in the face of climate change.

"Here on Cape Cod, we are acutely aware that many of climate change’s impacts will be felt and experienced here first, so we continue in our efforts to encourage and support our communities in taking steps to promote and build resilience so as not to be left unprepared and vulnerable," Williams said. "This is at the heart of everything that the Climate Collaborative was created for, believes and works toward."

Practical preparation, and people asking "how do we come together and develop collective action and live with this," said Piecuch, is "the kind of response we need to see."

The Cape Cod Times is investigating the effects of a rapidly heating planet on people who live on the Cape & Islands. This is part of the USA TODAY project Perilous Course.

Heather McCarron writes about climate change, environment, energy, science and the natural world. Reach her at hmccarron@capecodonline.com, or follow her on Twitter @HMcCarron_CCT

This article originally appeared on Cape Cod Times: Study: Atlantic current may collapse. How could it affect Cape Cod?