This Brief focuses on connections between climate change and health in the United States (U.S.) in 2017. It draws out some of the most nationally-relevant findings of the global 2018 Lancet Countdown on Health and Climate Change report with U.S.-specific data to highlight the key threats and opportunities climate change poses for the health of Americans. Climate Change Threatens Americans' Health Now Increases in heat and heatwaves pose a serious threat to health and labor productivity. More Americans are being exposed to extreme heat as a result of above-average and record-setting temperatures in the U.S., and heatwaves have been getting more frequent and lasting longer. This puts people at risk for heat exhaustion and heat stroke while worsening chronic conditions such as lung, heart, and kidney disease, which increases healthcare utilization and costs. Increased heat has health implications for laborers and has contributed to the loss of approximately 1.1 billion labor hours in the U.S. between 2000 and 2017. Increases in extreme weather events significantly threaten both health and health systems. In 2017, there were 16 extreme weather disasters in the U.S., from severe hurricanes to extensive wildfires, that each cost more than a billion dollars and together cost over $313 billion. While each type of disaster poses different threats to human health, they all can lead to death. The official death toll was estimated at 3,278 lives, though the actual number is likely much higher, highlighting the need for better surveillance. Climate change is elevating the risk of mosquito-, tick-, and water-borne diseases. Climate-sensitive vector-borne illnesses transmitted by mosquitoes, ticks, and fleas, including Lyme disease and West Nile virus, tripled between 2004-2016. Longer warm water seasons and increased water temperatures support pathogens and bacteria, like Vibrio, which can cause gastrointestinal illnesses, food poisoning, skin infections, and even death. Prevention of Further Dangerous Climate Change: Transitioning to Renewable Clean Energy Hospitals can lead America's efforts to transform the energy system. Increasingly affordable renewable energy sources in the U.S. have created the opportunity for a transition towards solar and wind energy, which results in cleaner air and water with fewer greenhouse gas (GHG) emissions. While this change is already happening, it must accelerate. Healthcare systems are major energy consumers, are well-placed to lead, and should ensure that their own operations are powered by renewable energy in order to minimize harm from their activities. Healthcare should extend its commitment to "do no harm" by divesting from the fossil fuel industry and investing in innovative solutions that will improve health now and for future generations. While public health departments across America are responding to climate change, healthrelated adaptation spending is inadequate for the challenge ahead. Forward-thinking public health departments and cities across America are already developing sh...