A car’s interior can become dangerously hot, even on days with moderate temperatures. Many people underestimate the speed and intensity of this heat buildup, incorrectly believing that leaving windows slightly open or running a brief errand prevents significant temperature increases. This oversight can lead to hazardous conditions in a surprisingly short amount of time.
The Science Behind Trapped Heat
A car acts much like a greenhouse. Sunlight, which consists of shortwave radiation, readily passes through the car’s windows. Once inside, this energy is absorbed by the vehicle’s interior surfaces, such as the dashboard, seats, and floor mats. These heated surfaces then re-emit the energy as infrared radiation, which is a longer wavelength.
Unlike the incoming shortwave radiation, the car’s glass largely traps this re-emitted infrared radiation. As more sunlight enters and is converted to trapped infrared heat, the interior temperature steadily rises, often reaching levels far exceeding the outside air temperature. This process explains why a parked car can feel like an oven even on a seemingly mild day.
Rapid Temperature Escalation
The temperature inside a parked car can rise swiftly. Studies indicate that a car’s interior can increase by 10 to 20 degrees Fahrenheit within 10 minutes. After 30 minutes, the interior temperature can increase by an average of one degree per minute, with the average car becoming 43 degrees hotter than the outside temperature within 60 minutes. On a day with an ambient temperature of 90 degrees Fahrenheit, the interior can reach 109 degrees Fahrenheit in ten minutes and 122 degrees Fahrenheit after 30 minutes.
Several factors influence this temperature increase. The outside air temperature plays a role, though interior temperatures can become dangerous even on mild days. Sunlight intensity and the duration of exposure directly affect how much energy is absorbed. The color of the car’s exterior also contributes, as darker colors like black and navy blue absorb more heat than lighter colors such as white or silver. Similarly, dark interior upholstery and dashboard materials absorb and radiate more heat, further contributing to the rapid temperature rise.
Health Risks of Overheated Interiors
Exposure to extreme heat inside a car poses health risks, especially for vulnerable individuals like children, pets, and the elderly. The body’s core temperature can rise rapidly, leading to conditions such as hyperthermia and heatstroke. Hyperthermia occurs when the body absorbs more heat than it can dissipate. Heatstroke, the most severe form of heat-related illness, happens when the body’s cooling system becomes overwhelmed.
Symptoms of heatstroke include:
- A high body temperature (104 degrees Fahrenheit or higher)
- Confusion, agitation, slurred speech, and seizures
- Nausea, vomiting, rapid breathing, and a racing heart rate
Without prompt intervention, heatstroke can result in irreversible organ damage to the brain, heart, kidneys, and liver, and be fatal. A child’s body temperature can rise three to five times faster than an adult’s, making them highly susceptible.
Strategies to Mitigate Car Heat
Strategies can help reduce the heat buildup in a parked car. Parking in the shade, under trees or in a parking garage, significantly reduces direct sunlight exposure. Using a windshield sunshade is another effective measure, as these reflective barriers block sunlight and can lower interior temperatures by up to 40 degrees Fahrenheit. Sunshades also protect interior materials from UV damage, which can cause fading and cracking.
Cracking windows open slightly offers limited effectiveness. Studies show that temperatures inside a car with cracked windows still rise to hazardous levels at nearly the same rate as those with closed windows. Relying on this method for safety is not advisable. The primary preventative measure is to never leave children, pets, or adults unattended in a vehicle, even for a short period.