The summer sun can turn a closed vehicle into a dangerous environment in minutes. This rapid and severe temperature increase is a direct result of physical laws working within the car’s cabin. Understanding the science behind this phenomenon is key to recognizing the profound risks involved.
The Physics of Solar Gain
The extreme heat inside a parked car is primarily caused by a process similar to the greenhouse effect. Shortwave solar radiation, which includes visible light, easily passes through the car’s glass windows and windshields. Once inside, this energy is absorbed by the vehicle’s interior surfaces, such as the dashboard, seats, and floor mats.
The absorbed shortwave radiation is then re-emitted by these surfaces as longwave infrared radiation, which is felt as heat. Unlike the incoming shortwave light, the glass is opaque to this longwave infrared energy, effectively trapping it inside the car. This continuous cycle causes a rapid accumulation of thermal energy and a dramatic temperature spike within the sealed cabin.
Rate of Temperature Escalation
The temperature inside a closed vehicle rises with alarming speed. Studies show that the greatest increase occurs almost immediately after the car is parked. A car’s interior temperature can rise by an average of 40 degrees Fahrenheit within a single hour, regardless of the ambient temperature outside.
Crucially, approximately 80% of this final temperature increase occurs within the first 30 minutes. For instance, on a day where the outside temperature is 70°F, the interior can reach 90°F in just 10 minutes. After 60 minutes, the interior temperature can be 43 degrees higher than the outdoor reading.
Physiological Impact and Danger
Exposure to these high temperatures quickly overwhelms the body’s natural cooling mechanisms, leading to a condition called hyperthermia. This occurs when the body absorbs heat faster than it can dissipate it, causing the core body temperature to rise dangerously. In the small, sealed space of a car, the air quickly becomes saturated with moisture, making sweating an ineffective way to cool down.
Children and pets are disproportionately vulnerable because their bodies heat up three to five times faster than an adult’s. A core temperature of 104°F is enough to cause heatstroke, and 107°F is often fatal. This uncontrolled rise can lead to irreversible damage to the brain, kidneys, and liver, with symptoms rapidly progressing from dizziness and weakness to confusion, convulsions, and death.
Factors Influencing Interior Heat
Several external and internal characteristics of a vehicle can modify how hot the interior becomes. The color of the car’s exterior plays a role because darker colors, like black, absorb more of the sun’s shortwave radiation than lighter colors, such as white or silver, which reflect more light. This higher absorption means darker cars tend to have higher surface and interior temperatures.
The effectiveness of slightly cracking a window is minimal, as research indicates it only reduces the final internal temperature by a negligible one or two degrees. Interior materials also heavily influence solar gain; dark dashboards, steering wheels, and seats absorb large amounts of solar energy. These surfaces can easily reach temperatures exceeding 180°F, radiating intense heat into the cabin air and contributing significantly to the overall temperature.