Lately, the heat has been off the charts all over the world, from Europe to Asia and North America.

Imagine this: Death Valley almost set a new record with a scorching 128 degrees Fahrenheit (53.3 degrees Celsius) on July 16, 2023.

Phoenix went through an unprecedented heatwave, with temperatures soaring above 110 F (43.3 C) for 19 straight days.

And the nights weren't much cooler, barely dipping below 90 F (32.2 C). Experts believe early July might have been the hottest week ever recorded.

It's not just the heat alone that's the problem; it's also the humidity. Scientists are diving deep into this, measuring something called "wet-bulb temperature" to figure out when heat and humidity together become too much to handle.

The mix of extreme heat and high humidity is a growing concern.

A decade ago, experts suggested that a wet-bulb temperature of 95 F (35 C) might be the tipping point.

That's like having a 95 F day with 100% humidity or a 115 F day at 50% humidity.

However, recent studies in controlled environments are showing that the limit could be even lower than we thought.

At Penn State University's Noll Laboratory, researchers are trying to pinpoint exactly when "too hot" really is too hot.

They had volunteers, all young and healthy, swallow special pills that keep tabs on their body temperature while they did light activities in a room where the researchers cranked up the heat or humidity.

The goal was to find the "critical environmental limit," or the point where the body just can't cool down anymore.

These experiments found that the danger zone starts at a wet-bulb temperature around 87 F (31 C) when the humidity is over 50%. That's equivalent to a 100% humid day at 87 F or a 60% humid day at 100 F (38 C).

When the mercury rises, staying hydrated and finding shade or air-conditioned spaces, even just for short breaks, becomes key to staying safe.

Some cities in the U.S. are setting up more cooling centers to help out. But with high energy costs and the risk of power outages during heatwaves or wildfires, finding relief from the heat can be tough for many.

In short, climate change is making our world hotter now, not just in the future. It's a challenge we're facing head-on, as we learn more about what our bodies can handle and how to stay cool under the sun.