When a car sits parked under the sun, its interior temperature can rise quickly, often reaching levels significantly hotter than the outside air. This rapid heat accumulation is a common phenomenon, yet its potential for danger is often underestimated. Understanding the mechanisms behind this heat increase and the factors that influence it can help in mitigating risks.
The Science of Car Heat
A car’s interior heats up rapidly due to a process similar to the “greenhouse effect.” Sunlight, a form of shortwave radiation, passes through the car’s glass and is absorbed by interior surfaces like the dashboard, seats, and floor. Once absorbed, these surfaces re-radiate the energy as longwave infrared radiation. This longwave radiation cannot easily escape back through the glass, trapping heat within the enclosed space. This trapped energy warms the air inside the vehicle, creating an internal environment hotter than the outside temperature.
Key Factors Influencing Temperature Rise
Several factors contribute to how quickly a car’s interior temperature rises. Ambient air temperature plays a role, as warmer outside conditions lead to higher peak interior temperatures. Direct sunlight exposure is a significant factor, with cars parked in the sun heating faster than those in the shade. The car’s exterior color also influences heat absorption; darker colors absorb more solar radiation, leading to a hotter interior.
Interior materials and colors also affect temperature accumulation. Darker upholstery and dashboard materials absorb more heat, intensifying the warming effect. Window tinting can reduce solar radiation entering the vehicle, helping to keep the interior cooler.
The Speed and Severity of Heat Buildup
Car interiors heat up rapidly, even on days that do not feel excessively hot. On a day with an outside temperature of 70 degrees Fahrenheit, the interior of a vehicle can reach 89 degrees Fahrenheit in 10 minutes and 113 degrees Fahrenheit after an hour. If the ambient temperature is 95 degrees Fahrenheit, the car’s interior can climb to 114 degrees Fahrenheit in 10 minutes and approximately 140 degrees Fahrenheit after an hour. Temperatures inside a parked car can be 43 degrees higher than the outdoor temperature after just one hour.
Surface temperatures within the car can become even hotter than the air. A dashboard can reach an average of 157 degrees Fahrenheit and a steering wheel can hit 127 degrees Fahrenheit after one hour in direct sun. Seats can warm to 123 degrees Fahrenheit, while dark dashboards or seats can even reach temperatures between 180 to over 200 degrees Fahrenheit. These high surface temperatures pose a risk of burns upon contact.
Understanding the Risks to Occupants
High temperatures in parked cars pose health risks, especially for children, pets, and the elderly. A child’s body temperature rises three to five times faster than an adult’s, making them susceptible to heat-related illnesses. Heatstroke occurs when the body’s core temperature rises above 104 degrees Fahrenheit, overwhelming its ability to cool itself. This can lead to organ and brain damage, and be fatal.
Symptoms of heatstroke in children include an altered mental status, seizures, delirium, and a core body temperature exceeding 104 degrees Fahrenheit. Pets, especially dogs, cannot effectively regulate their body temperature by sweating like humans, primarily relying on panting. Signs of heatstroke in pets can include excessive panting, drooling, vomiting, lethargy, and disorientation. Even with windows slightly open, the internal temperature can reach dangerous levels within minutes.
Strategies to Reduce Interior Temperatures
Several practical steps can help minimize heat buildup in a parked car. Parking in the shade is one of the most effective ways to keep the interior cooler, as it prevents direct solar radiation from entering the vehicle. Using a reflective windshield sunshade can significantly reduce interior temperatures by blocking sunlight from entering through the front windshield. Sunshades can lower the interior temperature by up to 40 degrees Fahrenheit and dashboard temperatures by a similar amount.
While cracking windows slightly might allow some hot air to escape, its effectiveness in significantly reducing the interior temperature is limited. Studies show that cracked windows make little difference in preventing dangerous heat levels. For those with remote start features, pre-cooling the car before entry can make the initial moments more comfortable. Covering seats and dashboards with towels can also help reduce direct heat absorption by these surfaces.