Research Highlights Featured Chart

February 12, 2025

Maritime emissions and infant health

Do stricter regulations improve health outcomes for newborns?

Tyler Smith

Source: Ui Inter

Maritime shipping emits as much fine particulate matter as half of global road traffic. Yet, historically, emission standards for ships have been weak compared to other forms of transportation. Stricter rules for ship exhaust, therefore, would appear to have the potential to significantly improve air quality near ports and coastal routes—where roughly half the US population lives—and lead to better health outcomes.

In fact, in a paper in the American Economic Journal: Economic Policy, economists Jamie Hansen-Lewis and Michelle Marcus found that stricter environmental regulations on ship exhaust significantly improved the health of newborn babies.

The researchers drew their conclusions from a 2012 US regulation requiring ships to use low-sulfur fuel within 200 nautical miles off the coast or to install abatement equipment. They compared the difference in birth outcomes in coastal areas with more or less ship traffic between 2007 and 2016, a period showing trends before and after the regulation took effect.

Figure 5 from the authors’ paper shows the event study figures for low birth weight and premature births, critical indicators of a baby's health and future well-being.

Figure 5 from Hansen-Lewis and Marcus (2025)

Panel A tracks rates of low birth weight. Before 2012, the difference in the trends in low birth weight between areas with more or less ship traffic was minimal. But after the regulation took effect, areas with heavy ship traffic saw a significant drop in low birth weight babies. By 2016, areas with the typical exposure to ship traffic had just over one fewer low birth weight babies per thousand births per year compared to what you would expect without the policy. Areas near heavy ship traffic had even greater improvements. Overall, the policy led to roughly 1,536 fewer low birth weight infants per year.

Panel B shows a similar pattern for premature births. Like low birth weight, there was no clear trend before 2012, but after the clean fuel rule, areas with more ship traffic experienced a noticeable decline in premature births. By 2016, although places with heavy ship traffic had even greater improvements, areas with the typical exposure to ship traffic had roughly two fewer premature births per thousand per year from the new rules.

Overall, the authors calculated that these improvements to infant health were equal to more than 70 percent of the estimated cost of the policy, $3.2 billion in 2020.

While the benefits of the environmental regulations took some time to fully materialize, this research, the first ex post evaluation of US maritime emissions regulation, clearly shows that stricter emissions standards on ships can lead to lasting improvements in public health.