Well over a century after the Age of Sail gave way to coal- and oil-burning ships, climate change concerns are prompting a new look at an old technology that could once again harness wind to propel commercial cargo ships — this time with the goal of reducing greenhouse gas emissions.

Imagine what looks like Boeing 747 wings with movable flaps, set vertically on a ship's deck. The vessel cruises under minimum power from its giant engine as computerized sensors adjust the fiberglass wings to take advantage of the wind's speed and direction. This wind-assisted propulsion saves a substantial amount of fuel and reduces the carbon belching from the ship's stack. Many experts think the idea has the potential to navigate the notoriously dirty shipping industry toward a greener future.

"Shipping is kind of unique," says Gavin Allwright, secretary-general of the International Windship Association (IWSA), a not-for-profit trade organization that advocates for wind propulsion in commercial shipping. From antiquity, ships used clean and free wind energy, "then we carbonized and now we're going back to zero carbon."

At least that's the hope.

The shipping industry could save fuel and cut down on emissions

About 90% of the world's goods — everything from soybeans to sneakers — are transported by sea. The tens of thousands of ships used to get these goods to global markets account for an estimated 3% of the world's carbon emissions each year, a figure that exceeds Japan's annual emissions. Left unchecked, the shipping industry's greenhouse gas emissions are expected to grow 50% by 2050.

Although commercial shipping wasn't included in the 2015 Paris Agreement, there's a huge economic incentive for the industry to decarbonize. The European Union's Emissions Trading System will cover the maritime industry beginning next year, meaning shippers will be forced to pay for their carbon emissions.

Also in 2024, the United Nations' International Maritime Organization (IMO) will grade each ship based on its cargo-carrying capacity and how many grams of CO2 it emits per nautical mile. Vessels with the poorest ratings will be required to take corrective action or risk not being allowed to operate. It's part of the IMO's ambitious goal to cut the shipping industry's annual carbon emissions at least in half by 2050.

Allwright says renewed interest in windships started to gain steam in the early 2010s, and today there are about 30 large commercial ships using one of a number of such technologies. Shipping giants Maersk and NYK are already experimenting with such systems. As many as 20 more are expected in the months ahead. So far, they are mostly "testbeds" to see if the concept is commercially viable.

In one recent trial, the 751-foot bulk carrier Pyxis Ocean operated by Cargill was retrofitted with two rigid sails, known as WindWings, inspired by those found on modern America's Cup racers. The vessel, carrying only water ballast, arrived in Paranaguá, Brazil, last month after an approximately 10,000-nautical-mile journey from Singapore.

The articulated fiberglass and metal wings, which stand 123 feet tall, use the force of the wind to create lift and move the ship forward. The wings can be folded on deck in case of unsuitable wind or heavy weather and while in port, where they would interfere with loading and unloading operations.

John Cooper, the CEO of BAR Technologies, which developed the WindWings, says it took considerable engineering and computer modeling to move the concept from high-tech racing boats to a commercial bulk carrier. On the America's Cup boats, "the hydrodynamic resistance is quite low," he says, compared to the "humongous" dynamic drag of a commercial ship.

On its first voyage last month after it was retrofitted, the 5-year-old Pyxis Ocean hit 16.2 knots (18.6 miles per hour) with the WindWings working in tandem with the ship's engine running at minimum power, Cooper says.

Before departing for Brazil, the ship even sailed briefly without the engine. "We pulled the anchor up, we put the wings up, turned them into their flying shape, and we cruised our way off berth," he says. "The crew were dumbfounded."

Variations on the rigid wing concept are being tried elsewhere. One system, first developed in the 1920s, is a bigger departure. "Rotor sails," or large carbon-fiber cylinders, move a ship along using a principle known as the Magnus effect, an aerodynamic force perpendicular to both the direction of the airstream and the axis of the rotor.

"I would say there's a competition right now," says Matthew Collette, a naval architect who teaches ship design at the University of Michigan. The wings on Pyxis Ocean are "more complicated, [but] potentially more efficient. The rotor sails are very simple, a little bit more limited in what you can do with them."

"But no one is talking costs openly," he adds.

In the case of WindWings, Cargill and BAR say a prototype system installed on a retrofitted ship is not a good indicator of ultimate cost, either for an initial installation or for operation. Ships built from the keel up to optimize the wing technology will show a clearer picture.

Allwright of the Windship Association estimates that, on average, wing technology amounts to $3 million to $4 million tacked on to a $100 million ship. "It's not insignificant, but it's also not a huge expense," he says.

With so many overlapping interests in the shipping industry, simply getting agreement to try a system such as WindWings is no small matter, according to Jan Dieleman, president of Cargill Ocean Transportation.

"You have to work together and somehow share the risk," Dieleman says. "An owner is not just going to put all kinds of installations on [a] ship if they don't know if somebody is actually going to pay them for that."

MC Shipping, a subsidiary of Mitsubishi Corp., owns the Pyxis Ocean, but Cargill, which operates it on long-term lease, agreed to put up the money for the WindWings installation, with help from a small EU subsidy. "We get the fuel savings because the fuel savings go to the operator and that's how we are going to make it work," he says.

Newer, cleaner fuels are another idea to cut emissions

On a retrofitted ship, such as the Pyxis Ocean, it could take anywhere from seven to 10 years to recoup the initial investment of wing technology, "which is not extremely sexy for the average commercial operator in this industry," Dieleman acknowledges.

The shipping industry is also looking ahead to new fuels, such as ammonia and methanol, that would be cleaner burning and put out less carbon — especially if used with new wind technologies. Those cleaner fuels, however, are likely to be much costlier than today's relatively cheap, but more polluting ones.

Fitting WindWings or a similar technology on a cargo ship or on oil tankers is no easy task, but it's simpler than retrofitting some other types of vessels, Collette says. "The deck space is a high priority on both vehicle carriers and container ships. So you're now giving up cargo as well as potentially modifying the ship design," he says. Despite those potential obstacles, earlier this year the French firm Zéphyr & Borée placed an order with South Korean shipbuilder Hyundai for five purpose-designed container windships with methanol-fueled engines.

Vessels designed and purpose-built as windships that burn cleaner fuel are the future that Dieleman envisions. It could cut a 10-year payback for WindWings to just three to five years, he says. In that case, it becomes "something very interesting on a ship that normally has a lifetime of, say, 20 to 25 years."

And fuel costs could be cut by nearly a third if a vessel were built specifically with WindWings in mind, according to Dieleman.

While the Pyxis Ocean continues its trial, BergeBulk, which owns and manages a fleet of some 80 bulk carriers, also plans to install WindWings on one of its vessels. And rotor sails made by Finland-based Norsepower have been installed on commercial vessels in China and Japan.

WindWings may be an entirely modern take on the old sailing ships, but the technology could revive some of the old clipper ship routes that have long fallen out of favor, BAR's Cooper says.

"You can see some of those old routes coming back," Cooper says. "You know, there's probably an argument for continually circling the world in a single direction rather than going backwards and forwards. Just keep going round the world to take advantage of the trade winds."

NPR's international affairs correspondent Jackie Northam contributed to this report.