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Is there any evidence that the heat from cars directly contributes meaningfully to temperature in cities? I’m genuinely curious (but skeptical). Edit: Some bac

Is there any evidence that the heat from cars directly contributes meaningfully to temperature in cities? I’m genuinely curious (but skeptical). Edit: Some back of the envelope math: Article says cars add 1.2 * 10^6 BTU of heat per day to Manhattan. Some rough math on my part suggests that Manhattan gets about 5.6 * 10^11 BTU of heat per day from the sun, 5 orders of magnitude more. The heat directly generated by cars is a rounding error.

deleted 2y ago
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atomicnumber3 2y ago
I always think it's kind of fun when we're reminded that the sun is literally a huge fusion explosion constantly going off in the sky. Using science to further appreciate the beauty of nature strikes me as very human.
coldbrewed 2y ago
The heat from vehicles isn't distributed spatially across rooftops/walls/trees where the heat might be dispersed; instead the heat from vehicles is concentrated and radiated adjacent to sidewalks (impacting pedestrians) and asphalt (which is effective at storing and re-radiating heat). Nor is it dispersed evenly throughout the day; congestion during rush hour will cause a spike of heat during the hottest part of the day with greater numbers of pedestrians experiencing that heat. Idling vehicles are also running air conditioning, and all of those idling/air conditioned vehicles will be creating an ambient atmosphere where their AC systems will have to run harder to create the same level of cooling. As you note solar heating likely dominates the overall heating of the city but I would fully expect that idling vehicles contributes meaningfully to the pedestrian and driver perceptions of heat.
- KorematsuFredt 2y ago
  BS. Most cars drive on freeways and interstates most of the time, especially the large trucks etc. traffic in residential areas is generally pretty low and it more only during mornings and evenings. This is just war on cars.
  - milkytron 2y ago
    In a lot of US cities, freeways/state highways are where a lot of commercial, retail, and entertainment destinations exist. The first homes usually aren't that far away either, and a lot of apartment complexes are built directly on state highways.
  - TomK32 2y ago
    Cars are used only 5% of the time, the rest of the day most of them sit around. They sit around in the sun, heat up and only disperse this heat during the night. Without those massive metal blocks in our streets, instead of large trees, the air could stay cooler during the day and night.
    - cman1444 2y ago
      Indeed. And those pesky metal and concrete office buildings sit there empty half the time soaking up heat as well. Not to mention the apartment buildings. In fact, let's just get rid of the whole city all together. That'll solve the problem.
milkytron 2y ago
Not sure how much heat is directly contributed by cars. But regarding the original comment, having dirt or vegetation will be less heat absorbing than even white or gray asphalt. Also it helps with runoff amongst other things. Even if cars directly aren't contributing all that much, the amount of empty parking spaces likely make their direct surroundings less hospitable than whatever the natural vegetation would contribute.
TomK32 2y ago
Do cars cease to exist when they are not driven? No. They sit in a parking space, most likely in the open air where they take away space for trees. Cars is why cities heat up. Put them into expensive parking houses or underground parking to have more surface space for trees.
- anamexis 2y ago
  I'm specifically talking about heat directly generated by cars.
happiness_idx 2y ago
While the raw numbers might suggest that the heat from cars is negligible compared to solar radiation, that overlooks the Urban Heat Island (UHI) effect and the synergistic feedback loops that make urban areas hotter. The UHI effect shows that cities are warmer than their rural surroundings because of concentrated heat sources like cars, buildings, and human activities. This local heat really impacts urban microclimates. Plus, the heat from cars creates feedback loops. More heat means more use of air conditioning, which releases even more heat exhaust, making the area even hotter. This cycle just keeps adding to the overall heat load in the city. So, even if the direct heat from cars seems minor on its own, it actually plays a significant role in making urban areas warmer.
- anamexis 2y ago
  I'm skeptical of that as well. It's my understanding that the Urban Heat Island effect is from roads and structures lowering albedo and absorbing more solar energy. https://www.epa.gov/heatislands https://www.epa.gov/heatislands https://www.heat.gov/pages/urban-heat-islands https://www.heat.gov/pages/urban-heat-islands https://www.annualreviews.org/content/journals/10.1146/annurev-environ-102014-021155 https://www.annualreviews.org/content/journals/10.1146/annur... A few of these do mention waste energy, but it seems to be a relatively small factor. And of waste energy, I would imagine that cars are themselves a somewhat small factor, compared to electric and natural gas usage.
- ch4s3 2y ago
  The UHI effect is mostly down to solar radiation and the thermal mass of the built environment. The sun heats the concrete during the day which radiates heat at night, so that the next day the baseline is higher than the surrounding area. Cars and human activities are a drop in the bucket as a previous poster shows.
TheOtherHobbes 2y ago
If Manhattan is getting 5.6 * 10^11 BTU of free heat energy every day, there isn't much of a reason to import more from outside. You could lose 4 orders of magnitude to inefficiency and still have plenty to run your cars.

deleted 2y ago

[deleted]

atomicnumber3 2y ago

I always think it's kind of fun when we're reminded that the sun is literally a huge fusion explosion constantly going off in the sky. Using science to further appreciate the beauty of nature strikes me as very human.

coldbrewed 2y ago

The heat from vehicles isn't distributed spatially across rooftops/walls/trees where the heat might be dispersed; instead the heat from vehicles is concentrated and radiated adjacent to sidewalks (impacting pedestrians) and asphalt (which is effective at storing and re-radiating heat). Nor is it dispersed evenly throughout the day; congestion during rush hour will cause a spike of heat during the hottest part of the day with greater numbers of pedestrians experiencing that heat. Idling vehicles are also running air conditioning, and all of those idling/air conditioned vehicles will be creating an ambient atmosphere where their AC systems will have to run harder to create the same level of cooling. As you note solar heating likely dominates the overall heating of the city but I would fully expect that idling vehicles contributes meaningfully to the pedestrian and driver perceptions of heat.

KorematsuFredt 2y ago
BS. Most cars drive on freeways and interstates most of the time, especially the large trucks etc. traffic in residential areas is generally pretty low and it more only during mornings and evenings. This is just war on cars.
- milkytron 2y ago
  In a lot of US cities, freeways/state highways are where a lot of commercial, retail, and entertainment destinations exist. The first homes usually aren't that far away either, and a lot of apartment complexes are built directly on state highways.
- TomK32 2y ago
  Cars are used only 5% of the time, the rest of the day most of them sit around. They sit around in the sun, heat up and only disperse this heat during the night. Without those massive metal blocks in our streets, instead of large trees, the air could stay cooler during the day and night.
  - cman1444 2y ago
    Indeed. And those pesky metal and concrete office buildings sit there empty half the time soaking up heat as well. Not to mention the apartment buildings. In fact, let's just get rid of the whole city all together. That'll solve the problem.

milkytron 2y ago

Not sure how much heat is directly contributed by cars. But regarding the original comment, having dirt or vegetation will be less heat absorbing than even white or gray asphalt. Also it helps with runoff amongst other things. Even if cars directly aren't contributing all that much, the amount of empty parking spaces likely make their direct surroundings less hospitable than whatever the natural vegetation would contribute.

TomK32 2y ago

Do cars cease to exist when they are not driven? No. They sit in a parking space, most likely in the open air where they take away space for trees. Cars is why cities heat up. Put them into expensive parking houses or underground parking to have more surface space for trees.

anamexis 2y ago
I'm specifically talking about heat directly generated by cars.

happiness_idx 2y ago

While the raw numbers might suggest that the heat from cars is negligible compared to solar radiation, that overlooks the Urban Heat Island (UHI) effect and the synergistic feedback loops that make urban areas hotter. The UHI effect shows that cities are warmer than their rural surroundings because of concentrated heat sources like cars, buildings, and human activities. This local heat really impacts urban microclimates. Plus, the heat from cars creates feedback loops. More heat means more use of air conditioning, which releases even more heat exhaust, making the area even hotter. This cycle just keeps adding to the overall heat load in the city. So, even if the direct heat from cars seems minor on its own, it actually plays a significant role in making urban areas warmer.

anamexis 2y ago
I'm skeptical of that as well. It's my understanding that the Urban Heat Island effect is from roads and structures lowering albedo and absorbing more solar energy. https://www.epa.gov/heatislands https://www.epa.gov/heatislands https://www.heat.gov/pages/urban-heat-islands https://www.heat.gov/pages/urban-heat-islands https://www.annualreviews.org/content/journals/10.1146/annurev-environ-102014-021155 https://www.annualreviews.org/content/journals/10.1146/annur... A few of these do mention waste energy, but it seems to be a relatively small factor. And of waste energy, I would imagine that cars are themselves a somewhat small factor, compared to electric and natural gas usage.
ch4s3 2y ago
The UHI effect is mostly down to solar radiation and the thermal mass of the built environment. The sun heats the concrete during the day which radiates heat at night, so that the next day the baseline is higher than the surrounding area. Cars and human activities are a drop in the bucket as a previous poster shows.

TheOtherHobbes 2y ago

If Manhattan is getting 5.6 * 10^11 BTU of free heat energy every day, there isn't much of a reason to import more from outside. You could lose 4 orders of magnitude to inefficiency and still have plenty to run your cars.