(Photo : Air National Guard)

I've been too hot to sleep, too hot to exercise and too hot to work, but I had no idea it could get too hot to fly. What happens?

American Airlines cancelled 50 flights last week in the southwest United States giving excessive heat as the reason the planes could not fly. Many people have experienced the weather being too cold to fly. Ice on wings and on runways make conditions unsafe for commercial flight. But what happens when the temperature reaches over 118 degrees?

Physics explains why flying when it's too hot is not a matter of danger. Given the circumstances, it is physically impossible.

Some planes, like the Bombardier CRJ airliners have a maximum operating temperature of 118 degrees. Other larger planes from Boeing and Airbus can handle hotter temperatures of 126 degrees. The reason that these planes cannot fly when it is so hot is the air density. When temperatures rise, the air density decreases because gas expands and increases the volume of the air. Less air density generates less lift.

One way to counteract the extremely warm temperatures and low air density is by adding speed to achieve more lift. Unfortunately, you need more runway room to reach that speed. The runways at airports are only so long -- and usually not long enough for high-temperature takeoff.

Perhaps with a new report that was released earlier this month detailing a future increase in heatwaves across the world, Phoenix and other airports will consider lengthening their runways to compensate for the hot weather. The temperatures seen last week across the southwest are not an anomaly. They could be part of the new normal as Earth's climate heats up rapidly.

"Across the world we're finding that we can link unusually warm weather events to climate change," says climate researcher Andrew King.

Climate change is the driving force behind the heatwaves that affected the southwest over the past week. In the future, these types of heatwaves will become more common as the global temperature heats up and carbon emissions fail to decrease. It is well accepted in the science community that man made carbon emissions are causing the rise in temperatures worldwide.