You can chug water, sit in the shade, and pray for a breeze… but once temperatures hit a certain point, none of that will save you. That’s the terrifying reality behind a little-known killer: wet-bulb temperature.

Unlike dry heat, which feels like standing in an oven, humid heat clings to you like a sweaty blanket and makes it almost impossible for your body to cool down. At a certain threshold, called the wet-bulb limit, sweating stops working. Once this point is crossed, your body can no longer regulate its temperature, and heat stroke becomes deadly fast. No amount of hydration or shade will help. The only way to survive? Artificial cooling, like air conditioning.

But here’s the problem: parts of the world are already hitting these dangerous levels. With just 2°C of global warming, up to a third of the Earth’s land, including much of India, China, and the eastern U.S., could regularly experience deadly heat. Go to 4°C, and over 60% of land areas are affected.

But relying solely on air conditioning isn’t a perfect fix. It’s expensive, not universally accessible, and contributes to climate change by increasing energy demand. In many vulnerable areas, AC isn’t even an option. And when power grids fail, whether from overloads or other extreme weather, millions could be left helpless.

So what do we do? The PBS video below suggests solutions: transitioning to clean energy, redesigning cities to reflect and absorb less heat, planting more trees, upgrading power infrastructure, and prioritizing support for at-risk communities.

Extreme heat isn’t just uncomfortable, it’s becoming a public health crisis. And the science is clear: unless we act now, “too hot to handle” might become “too hot to survive.”