The world's enormous thirst for oil is quenched by supertankers that move nearly two-thirds of all global crude from producers to markets via the high seas. But the business isn't all smooth sailing. That oil must flow through a series of geographical chokepoints, and disruptions to these vital areas—some of which are located in politically unsettled places—can have serious impacts.
Sarah Ladislaw, director of the Energy and National Security Program at the Center for Strategic & International Studies, says chokepoints are where the logistics of moving oil around the world bang up against geopolitical realities like political unrest and terrorism.
“Places like the Strait of Hormuz and the Strait of Malacca get a huge amount of attention from the security community because of the enormous volume of oil moving through them, and the impacts there will be to world economies, markets and consumers if there's a significant disruption at those places.”
The narrow, crowded waters of such chokepoints are ready-made for problems, whether by geopolitical conflicts or environmental disasters.
A big tanker hauls enough oil (up to 2 million barrels) to fill the gas tanks of 5 million cars. Using an economy of scale on direct, well-traveled routes, tankers move oil for just pennies a gallon—but their concentrated traffic can have consequences for the oceans.
The most obvious impacts are from oil spills, a particular risk at chokepoints where high traffic and tricky geography make safe navigation difficult for tanker ships, which average near the size of the Empire State Building. Chokepoints are also in close proximity to coastal ecosystems and sometimes to large human populations, such as in the Turkish Straits, which bisect Istanbul.
The Turkish Straits and surrounding waters have witnessed hundreds of maritime accidents and several significant spills over the decades. Their consequences, paired with onshore developments and other shipping-produced oil contamination like ballast and bilge water releases, have wreaked havoc with a fragile aquatic environment. Marine species have paid a heavy price, from tiny crustaceans to larger fish species that once filled increasingly empty nets.
The Strait of Malacca, just 1.77 miles wide at its smallest and the carrier of one-third of the world's commercial activity, has also seen its share of spills, and oil here poses particular threats to coastal seagrass beds and mangroves—which tend to trap oil—not to mention to human development along the shores. Preventing them is a big concern in a congested waterway of moving sand bars and dangerous rocky outcrops.
“A major oil spill incident the size of the Exxon Valdez incident would surely cover a huge part of the Strait and would cause irreparable damage to the ecosystem, fishery, biodiversity and the tourism industry,” concludes a 2007 study from the Maritime Institute of Malaysia.
While spills are destructive and dramatic, other impacts of tanker traffic are far less visible.
When tankers discharge their cargo at oil refineries, they take on ballast water to keep them stable in the sea. When those tankers return to get more oil, the ballast is pumped out—carrying with it living organisms. This process moves plankton and microorganisms long distances and introduces them to new environments with unforeseeable effects.
Tankers and other cargo ships often burn high-sulfur bunker fuel, banned on land and in some coastal waters including those around the U.S. because it creates large amounts of air pollution. Crude oil takers also emit volatile organic compounds like methane and heptane into the atmosphere when crude is loaded, stored and transported. The Norway-based research organization SINTEF estimates that emissions from a typical 100,000-ton tanker load represent 2,200 barrels of oil.
And big tankers are loud. The noise they produce can be particularly troubling to marine mammals because it interferes with acoustic communication.
All these impacts are magnified in concentrated chokepoint traffic, which sometimes transits near or through areas of particular importance to the ocean ecosystem. On California's busy coast, for example, tanker traffic heading to Bay Area ports must pass through three interconnected National Marine Sanctuaries. In addition, the Turkish Straits and the Strait of Hormuz are key environmental gateways between larger aquatic ecosystems—and some of the world's most heavily travelled tanker routes.
Meanwhile, tradeoffs between speed and the environment are perhaps nowhere more obvious than at the Panama Canal, which has seen its prominence as an oil conduit shrink because tanker sizes have grown. Despite an ongoing expansion, the waterway, as narrow as 110 feet in places, isn't able to accommodate the largest classes of oil tankers, which must instead ply alternate routes.
Avoiding the canal for a trip around Cape Horn adds about 8,000 miles to the trip and requires additional time and fuel. But expansion of the Panama Canal has also raised anxieties. Canal Zone forests are filled with unique flora and fauna that have comingled here over the eons at the meeting point of North and South America. It's feared that widening the canal may disrupt terrestrial wildlife corridors while facilitating an artificial aquatic one that lets species migrate from ocean to ocean, where they can have unknown impacts on ecosystems.
Ships leaving the canal carry millions of gallons of fresh water with them out into the ocean. The human-made lakes that help supply this water also quench the thirst of people in Panama City, and supplies may become scarce—especially if a changing climate dries out the region. Meanwhile, canal operations also mix ocean waters with the lock system, raising fears that the vital freshwater supplies including Lake Gatun, Panama's primary source, could become too saline with increased ship size and traffic. Canal backers insist the impacts will be neglible.
The impacts are even being felt far from Panama's shores. Widening the canal has already launched a chain reaction in which ports along U.S. coastlines need to dredge and deepen their own waterways—or miss out on the boon of increased traffic from the giant ships the new canal will allow through. Dredging muddies the waters, literally, and can introduce buried seafloor metals to the ecosystem or choke off grasses or other key habitats during seafloor relocation.
Despite the environmental and geopolitical challenges of oil chokepoints, they may also deliver some unexpected benefits along with the crude that powers our economies. Because countries depend so much on oil, for now, it's in everyone's best interest to protect the chokepoints from disruption so they've become places where stakeholders work their hardest to prevent problems. That's created international cooperation and could even open new doors.
“Over the long term, China and other regional sea powers need to cooperate on this issue,” notes Ladislaw. “So that oil transit through Hormuz and Malacca may be a really good way of engaging what people think will be a rising sea power in China to work on an area of common interest.”