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Ships play a central role in the global trade of goods, but they also make noise–which might affect undersea creatures like whales that depend on sound for communication and navigation. M. Scott Taylor investigates this issue in “Saving Killer Whales Without Sinking Trade: A market solution to noise pollution” (Property and Environment Research Center (PERC), September 25, 2025). Taylor (no relation) begins:

Maritime shipping is key to global trade, and international trade is key to prosperity worldwide. Today, approximately 80 percent of world trade by volume and over 60 percent by value is transported by ships. This trade brings new goods, technologies, and ideas from around the world and is critical to maintaining our standard of living and growing it into the future. Despite these benefits, shipping—like all economic activity—has environmental impacts.

Maritime shipping is responsible for perhaps 3 percent of global carbon emissions and a significant share of the world’s particulate and sulfur dioxide emissions. International organizations like the International Maritime Organization and regional governments like the E.U. have set new regulations and plans to reduce these impacts over the coming decades. There is, however, an impact of shipping on the environment that researchers have only recently recognized—underwater noise pollution—that may have deleterious effects on marine mammals. …

There is now widespread recognition that over the post-World War II period, maritime shipping has raised ambient noise levels in the world’s oceans. While estimates of the long-term change in ambient noise are somewhat speculative, one commonly cited source¹ suggests ambient ocean noise has risen by three to four decibels (dB) per decade since the 1950s. This increase, tied to a simultaneous increase in maritime shipping, raised the ambient noise level in the low-frequency zone most relevant to marine mammals from approximately 52 dB in 1950 to more than 90 dB by 2007 …

Not surprisingly, marine biologists and ecologists have started to study the impact of rising ambient noise levels on marine mammals. The reason is simple: Sound to marine mammals is much like sight is to humans—it is their primary sense for moving through the world around them. Low-frequency sounds (less than several hundred Hz) may be interfering with whale communication and social calls, whereas higher-frequency sounds (greater than several hundred Hz) potentially interfere with the echolocation employed to track prey. Therefore, the sounds emitted by maritime shipping may affect almost all aspects of whale life, making it more difficult to communicate, socialize, and hunt.

Thus, two questions arise. First, is there some evidence that underwater sound affects whale populations in a negative way (and what would that evidence look like?). Second, if so, what might be done about it.

For evidence, Taylor offers an analysis of the “Southern Resident killer whales,” who spend most of their year living in what is called the Salish Sea, off the coast of Seattle in Washington state and Vancouver in British Columbia. This is “perhaps the most studied whale population in the world, with detailed health and genealogical information on births and deaths accurately measured since the late 1970s.” Taylor points out that as shipping into this area has increased, the whales living closer to the main ports have seen a decrease in population, while those living further north and away from the ports have seen an increase–suggestive, but one can imagine a variety of explanations.

Thus, Taylor zooms in on the variations in shipping across years, often caused by factors like the 2001 dot-com recession or the 2008-09 Great Recession. As it turns out: “For example, at age 40, a Southern Resident killer whale is over 30 percent more likely to die in a noisy year.” Also, “[i]n years of peak fertility, noisy years lower the probability of a subsequent successful birth by over 25 percent.” The broader question of how shipping noise affects whale populations around the world is clearly worthy of additional study, but for present purposes, Taylor advances to the second question of what might be done.

Of course, what economists call a “command-and-control” approach might just require every ship to install equipment to reduce noise. But as economists also like to point out, there might be an array of ways to reduce noise: along with quieter engines, perhaps a quieter propeller (or even just polishing the existing propellers), redesigning ducts that direct water to the propeller, perhaps travelling at different speeds (recognizing that a faster ship for less time might be preferable to a slower ship for a longer time), perhaps ships of different hull design or different sizes. Indeed, the best answer for minimizing the noise involved in shipping a certain amount of cargo may not be knowable in advance, because it would require research and experimentation over time.

Taylor proposes a way of measuring the underwater noise from ships, and suggests that marketable permits could be used. The idea of such permits is that a shipping company must have a permit for the underwater noise it emits. The original distribution of permits can be done by handing them out to existing shipowners, or by requiring that existing shipowners buy them (perhaps through an auction). Shipping companies that find ways to move cargo more quietly will have extra permits, which they can sell to other firms. At a minimum, such permits could prevent the amount of underwater noise from rising; in addition, the amount of noise allowed by a given permit can be preset to diminish over time.

The basic idea here is that, in this case, public policy should focus not on dictating a command-and-control solution, but instead to set a goal for how much underwater noise from shipping should be reduced, and then to give shipowning firms a financial incentive to innovate and experiment to meet and exceed that goal.

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