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How hot can the interior of a car get – and how quickly?

Written by on November 12, 2015 in Science



By Jon Sutz


(1) Summary

(2) How hot does it get in a car, and how quickly?

(3) Doesn’t leaving the windows cracked an inch or two make a difference? No.

(4) Quotes by experts


(1) Summary

Imagine your body could not sweat, and was covered in thick fur.

Now, imagine someone who can sweat, who isn’t covered from heat to toe in fur, and who professes to love you, left you in a car, with the windows all or most of the way up – for 10, 20 or more minutes, during spring, summer or fall months.

How quickly would you begin to feel uncomfortable, dizzy, pass out, or die?

This, sadly, is the position that some dog owners leave their “best friends,” because they don’t know (a) how even the most basic information about dog physiology, or (b) why it’s incredibly dangerous to leave them in cars, even for a short period of time, in what seems to be cool temperatures.  And as a result, each year across America, thousands of dogs suffer organ damage, or die agonizing, preventable deaths, due to heatstroke.

This page is devoted to providing dog owners and lovers, police departments, animal shelters with rigorously-vetted scientific information on why it is so dangerous to leave a dog in a car, and why:

  • Dogs can begin to suffer brain damage in as little as 10 minutes, when left in cars, even with the windows partially open
  • Dogs have died from heatstroke in such conditions, even in temperatures as low as 70 degrees
  • Regardless of the exterior temperature, the interior temperature of a car left in anything other than cold conditions, even with the windows partially open, rises 19 degrees in the first 10 minutes, and 29 degrees in the first 20 minutes.


(2) How hot does it get in a car, and how quickly?

This chart, produced by, helps to answer that question.  It is based on research produced by Jan Null, CCM, Department of Earth & Climate Sciences, San Francisco State University.

You can download, print and share HeatKills™ posters and handouts featuring this chart, here.

Animation shows how quickly interior temperature of car can rise in sunlight

This animation was developed by General Motors, to showcase how quickly the interior temperature of an enclosed car can rise to deadly levels:

Video from the Red Rover – My Dog Is Cool campaign:

From the British Columbia (Canada) SPCA:

Report by American Academy of Pediatrics on heat stress in enclosed vehicles

Abstract: Each year, children die from heat stroke after being left unattended in motor vehicles. In 2003, the total was 42, up from a national average of 29 for the past 5 years. Previous studies found that on days when ambient temperatures exceeded 86°F, the internal temperatures of the vehicle quickly reached 134 to 154°F. We were interested to know whether similarly high temperatures occurred on clear sunny days with more moderate temperatures. The objective of this study was to evaluate the degree of temperature rise and rate of rise in similar and lower ambient temperatures. In addition, we evaluated the effect of having windows “cracked” open.

Pediatrics 2005 McLaren e109 12



(3) Doesn’t leaving the windows cracked an inch or two make a difference? No.

A study conducted by Red Rover demonstrates that the difference in interior temperature between a car with the windows fully closed, and those that are cracked a few inches, is negligible. See bottom of page here.

Red Rover cracked window study excerpt

Excerpt from Red Rover study.

Two frustrated veterinarians simulated what a dog endures — using themselves as a guinea pigs — in cars with the windows partially down

Dr. Ernie Ward is a veterinarian you should know. He’s spent many years devoting himself to not only treating illnesses in dogs and cats, but in developing better means for preventing them. Learn about Dr. Ward here.

To answer the question of how hot a car can get, over time, Dr. Ward literally locked himself in a car and videotaped his commentary, to give indication of what a dog experiences when trapped in such an environment:

Adrian Walton, DVM owns the Dewdney Animal Hospital in Maple Ridge, British Columbia. After encountering the unawareness and counter-knowledge that persists in regards to the dangers of leaving a dog in a car, Dr. Walton decided to subject himself to sitting in a car, with the windows open a few inches, for thirty minutes. Here is the result.


(4) Quotes by experts

“Children have died in cars with the temperature as low as 63 degrees. Basically the car becomes a greenhouse. At 70 degrees on a sunny day, after a half hour, the temperature inside a car is 104 degrees. After an hour, it can reach 113 degrees.”

Jan Null, adjunct professor at San Francisco State University (source data here)

“When temperatures outside range from 80 degrees to 100 degrees, the temperature inside a car parked in direct sunlight can quickly climb to between 130 to 172.”

Centers for Disease Control and Prevention

“In terms of heat-rise over time, it makes very little difference whether a car’s windows are closed or partially open. In both cases, a car’s interior temperature can rise approximately 40 degrees within one hour, even when the exterior temperature is only 72°F.”

American Academy of Pediatrics study (2005)

“Even on a relatively cool day, the temperature inside a parked car can quickly spike to life-threatening levels if the sun is out, researchers at the Stanford University School of Medicine have found. They hope their findings will put to rest the misconception that a parked car can be a safe place for a child or pet in mild weather. ‘There are cases of children dying on days as cool as 70 degrees Fahrenheit,’* said lead author Catherine McLaren, MD, clinical instructor in emergency medicine. Though past research has documented the temperature spike inside a car on extremely hot days, this is the first time anyone has looked at cooler days, she added.”

Stanford University press release: “Parked cars get dangerously hot, even on cool days, Stanford study finds” (2005)

(* In Charlottesville, VA, a toddler died of heatstroke after being left in a car, on a day in which the outside temperature did not exceed 66 degrees.)

“Never leave your pet in a parked car when the outside temperature is above 70 degrees. Not even with the windows partway down, not even in the shade, not even for a quick errand. Dogs and cats can’t sweat like humans, so they pant to lower their body temperature. If they’re inside a car, recycling very hot air, panting gives no relief, and heat stroke can happen quickly.”

Michael Dix DVM, Medical Director, Best Friends Animal Society

“Heat stroke can permanently damage a pet’s health very rapidly. The change of only a few degrees to a dog’s normal body temperature can quickly result in coma, organ dysfunction, permanent brain damage or even death.”

Jules Benson, DVM, Medical Director, Pet Plan Pet Insurance




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About the Author

About the Author: My name is Jon Sutz. I am a dog-loving multimedia graphic designer, writer and creative consultant, in Charlottesville, VA (bio). But the most important, joyous job I've ever had, was as "dad" to Shayna, the miracle dog who helped to save my life after 9/11, and about whom I wrote my first book, "Saved By Shayna: Life Lessons From A Miracle Dog." Learn more about Shayna at her website. In tribute to Shayna, I developed to help raise awareness of the dangers of leaving one's dog in a hot car. .


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