The Operating Environment and Aircraft Performance

    As an aircraft goes to and from multiple locations throughout the course of one day, the issues that come with rapid changes in environmental conditions must be taken into consideration when making a flight plan, maintenance, and general wellbeing of passengers and flight crew. Specifically, as it comes to heat, heat can lead to many different issues, such as:

• Increased take-off distance is required since the air is less dense, more time is needed to get to the needed speed for a successful takeoff.
• A change in Density Altitude! This is apparent altitude, or what the altitude would have to be to get the same effects in standard conditions.
• As the air warms up, the density decreases due to the area expanding. This creates a less than optimal air content for flights, making cooler hour flights advisable.
• Higher temperatures can also lead to higher humidity potential, further decreasing the density of the air. As water molecules are less dense than Oxygen and Nitrogen molecules, they tend to overall lower the given area's density

These all combined lead to the issues of temperature being a very important environmental factor, and usually is lead into the concepts of changes in overall global temperatures, solar minima and maxima, and global warming. All of which have varying degrees of consensus and solutions. One thing can be said, however, is that any change in temperature, be it hot or cold, will change how humans plan flights and overall quality of life during said flights.

Source: https://www.researchgate.net/figure/Rendered-simulation-of-the-arctic-mirage-The-inferior-mirage-occurs-when-there-is-a_fig6_221546305

Sources:

https://www.faasafety.gov/files/gslac/library/documents/2011/Aug/56396/FAA%20P-8740-02%20DensityAltitude[hi-res]%20branded.pdf