Health care in the United States ranks among the best in the world. But the Hippocratic oath of “do no harm” goes only so far. Many Americans rightly fear hospitals because of real-life demons like MRSA, the antibiotic-resistant staph infection that dwells in hospitals like silver foxes dwell in Florida. But there may be a more insidious way in which hospitals hurt more than they help. Research says our health care system churns out greenhouse gases and other pollutants — making people sick in the process. A recent PLOS ONE paper found that:

If the U.S. health care system were a country, it would produce more greenhouse gases than the United Kingdom.

That would place it 13th in the world in greenhouse gas emissions. The study traced other environmental impacts, such as acid rain and smog formation, to the health care system too. All that pollution, in turn, takes a significant toll on public health.

The U.S. health care system not only has the heftiest price tag in the world — with Americans spending more than $3 trillion on health care in 2014, up from $1.9 trillion in 2004 — but it also consumes massive quantities of energy, largely in the form of electricity to power hospital ventilation systems and equipment, as well as to manufacture drugs and devices. Collaborators Matthew Eckelman of Northeastern University and Jodi Sherman of Yale University School of Medicine stumbled on a 2009 study of the health care system’s greenhouse gas emissions when they thought, “Wouldn’t it be great to get a whole picture of the health care system overall?’’

To measure greenhouse gas and other emissions from not only health care itself, but the industries that support it — such as pharmaceutical manufacturing and power generation — they used an economic model of dollar flow between industries and calculated the emissions generated per dollar spent. They found that from 2003 to 2013, the health care system’s greenhouse gas emissions rose 30 percent, making up nearly 10 percent of the U.S. total in 2013. Power generation accounted for a whopping 36 percent of those emissions, the biggest source by far.

That year, the health care system also accounted for significant proportions of national air pollution, including 12 percent of acid rain, 10 percent of smog formation, and 9 percent of lead, carbon monoxide and other common air pollutants. The researchers used another model to estimate that this resulted in 470,000 disability-adjusted life years, or DALYs, a metric of years lost due to sickness, disability or premature death. That’s within the same ballpark as the number of lives lost each year due to preventable medical errors. Considering how much the U.S. spends on health care — with facilities paying electric bills and doctors spending their salaries on gas, for instance — the environmental impact “makes sense,” Eckelman says. But he found the public health effects “surprising.”

To be sure, the study only estimates environmental and health effects. For instance, the economic model “provides a very rough average” of emissions from the power generation sector, even if a coal-fired power plant in Pittsburgh generates far more emissions than a hydroelectric plant outside Seattle, says Paulina Jaramillo, of Carnegie Mellon University. “You need to look at these as the aggregate for the entire health care system, not specifically this hospital where I go to see my doctor,” she says. Eckelman acknowledges the use of national averages as “a drawback.”

Still, the study shows a clear upward trend and offers the most comprehensive measurement of the U.S. health care system’s environmental footprint to date. “It’s provided the first statement of the size of the problem” and a starting point for future research, says Robert Lillywhite, of the University of Warwick. “The scary bit is that the provision of health services kills people … Would we actually save more lives than we lose from reducing health care services?” Eckelman says he and Sherman don’t advocate trading off patient care with environmental impacts, but instead minimizing emissions in ways that don’t affect care, like installing more energy-efficient lightbulbs.

While we can say that consuming less electricity is crucial for softening the health care system’s environmental impacts, Eckelman notes that we can’t make specific recommendations for any single health care facility just yet. “The hope is that this article can help get the conversation going,” he says. “Energy efficiency is something clinicians should care about because it’s health. It’s not directly your patient’s health, but it is public health.”