sk Jodi Sherman to identify a culprit in global climate change, and you’ll get an unexpected answer. The anesthesiologist from Yale University doesn’t name the usual suspects—carbon dioxide, like the kind that spews out of our cars, or methane, the gas packed into every cow burp. Instead, she points a finger at anesthesia, the tool most essential to her trade. “And it’s just being released into the atmosphere with no control,” she says. Carbon dioxide is perhaps the most famous climate-changing chemical, but some of the gases used to knock people out in the operating room are many times more potent. Between sedation for surgeries, manufacturing medical supplies, and keeping the power on in hospitals, the medical sector is responsible for quite a few emissions. In the United States, 10 percent of all greenhouse gas emissions come from the healthcare system. And in the United Kingdom, the National Health Services estimates that anesthesia alone accounts for around 5 percent of the carbon footprint of the health care system. While no doctor would ever suggest performing, say, open heart surgery without anesthesia, many are taking steps to mitigate the effects of the drugs they use.