What brings you to the emergency room today? Increasingly, the answer could be climate change.

It worsens existing ailments and causes people to suffer from new afflictions. Moreover, entire health systems are beginning to recognize that threats from climate change will have a big impact on their operations, according to a recent six-part series in Axios written by Tina Reed, Andrew Freedman, Arielle Dreher and Oriana Gonzalez.

“The growing threats to human health only promise to get more complex and expensive, and health systems have to make major changes to how they prepare for those threats,” Reed wrote.

Virtually all climate change impacts carry potential medical consequences: Smoky air from a wildfire can exacerbate asthma, heat waves can trigger life-threatening heat strokes, and, as climate emergencies become more severe, they are taking a toll on more people’s mental health.

It’s no wonder the World Health Organization has called climate change “the single biggest health threat facing humanity.” It’s driving massive shifts in the way diseases impact communities that haven’t experienced them before.