18 ms·

Countering climate change with cool pavements

82 points by 35_candelas 5y ago

guerrilla 5y ago
> “cool pavements” [..] reflect more solar radiation and emit less heat than conventional paving surfaces. Darn, I thought they were going to talk about using heat pipes driven deep into the ground to turn the pavement into a heat sink and was wondering how they were going to get the pavement to conduct heat to the heat pipes. Now I'll never know. ;)
clairity 5y ago
> “Conversely, by reflecting light — called incident radiation — onto nearby buildings, cool pavements can warm structures up, which can increase AC usage in the summer and lower heating demand in the winter.” this is one of the reasons why i'm an advocate for street trees, and urban foliage in general (cuts down both incident and reflective radiation), and why i'm maddened when i see urban trees cut down or cut back (as been happening quite often in my urban neighborhood in LA). the tree trimmers i see doing this have no idea what they're doing, being low-paid laborers paid only to run a chainsaw/trimmer, not to contemplate consequences or consider other options. trees take decades to become effective shade, and minutes to butcher irreparably. that's not to put down cool pavements, which are really cool (haha), but that trees can provide all the same benefits and more, which makes it the better first option, with cool pavements being reserved for where tree shading is difficult or impossible (like roadways and parking lots).
- pharmakom 5y ago
  I also like urban trees but remember they cost a fortune to maintain! For example, urban trees have to be expertly managed for disease along transit lines.
  - frosted-flakes 5y ago
    Why would they cost a fortune to maintain? Apart from leaf collection and end-of-life removal, what costs are associated with street trees?
    - godelski 5y ago
      They require water, which requires irrigation (may not already be in place and of course has logistical problems), trees also root systems can lift and crack sidewalks/pipes/other things, you now have biological contaminants, there's bugs and fungus and things that can spread, and so much more. I'm not saying we shouldn't do this. I really like seeing plant life in cities and I think it really makes a psychological difference (I _love_ living in a city with a lot of green spaces and trees everywhere). But it is nowhere near as simple as placing a tree in the ground and cleaning the leaves.
      - ClumsyPilot 5y ago
        "now have biological contaminants, there's bugs and fungus" Dude, we have rats running around, pigeons nesting and pooping, what biological contaminants?
        godelski 5y ago
        Just because biological contaminants exist doesn't mean adding more creates more issues. More trees also means more rats and pigeons. What's your argument? That just because we already have a bad thing doesn't mean that a similar bad thing isn't bad? That doesn't make much sense and is a pretty lazy argument.
        ClumsyPilot 5y ago
        Either way, rats and pigeons feed on garbage, they dont eat oak trees. We need to have less takeaway left on the street and garbage bins that are cleaned up on time.
      - Ma8ee 5y ago
        How much irrigation that is needed very much depends on where you are and what kind of tree. After the first few years it take to settle, trees have deep roots and rarely need watering. And I have never heard of trees contribution negatively to "biological contaminants", whatever that means. Rather, trees contribute to a cleaner and healthier environment.
  - berikv 5y ago
    The pavement replacement won’t be free either, I suppose. I’ve never heard of a government cutting trees as a cost saving, however I didn’t look for that either. I think that, once trees are there, people will be happy to pay the few dollarcents per year for their maintenance.
- harmmonica 5y ago
  from one LA resident to another, amen to that. we were just walking down our street this morning and discussing, for the umpteenth time, whether our neighbors would actually be willing to take care of trees if we went out and bought them and planted them. the problem, as other commenters have pointed out, is that they do require upkeep, but since they're living/breathing things the more hardy ones can really be abused and still survive. The question is how do you incentivize the people who benefit from the trees--the residents, businesses, other local stakeholders--to actually maintain them? on our street there are countless trees that were likely planted decades ago, but a lack of care by the residents makes them mere shadows of their potential. and for anyone interested, LA's a great example of how trees provide a return on investment (actual dollar return outside the tremendous ecological benefits). go onto google maps and look at the satellite view. people who have never been here can point out the expensive neighborhoods because they are the greener ones.
  - clairity 5y ago
    LA has an woefully underpublicized street (and lawn) tree program, where you can get free trees if you agree to take care of them (which is mostly just periodic watering), so you wouldn't even have to buy them yourself. for street trees on the parkway (the patch of ground between the sidewalk and street), you don't technically even need the permission of the owner, although the owner might not be amenable to watering them then. apartment dwellers (like me) can get trees planted on the parkway just by agreeing to take care of them on behalf of the owner.
    - harmmonica 5y ago
      it's true, that's exactly how we got our street tree, but a) it took an extremely long time to get the tree in the first place and b) the tree itself was rather lackluster, though now we're on year 3 of it and it's... ok. if I knew then what I know now I would've just gotten my own tree (one of the ones on the approved list) to get a nicer tree up front. as for planting the trees without the permission of the resident responsible for that parkway, like I said in that previous comment, it doesn't do much good if the folks don't take care of them. we've also learned the hard way that doing things that seem additive to the hood are not always taken that way by neighbors and can cause conflict. been on the end of that a couple of times already. that said, maybe I'll stop talking about doing this and actually try it and see what folks say.
- puffyvolvo 5y ago
  While I initially would prefer the idea of more street trees the nagging voice in the back of my head continues to worry about unintended consequences. A big one regarding more trees is more maintenance, you've already pointed out how terrible maintenance can be, and lawns alone are an incredible example of just how inefficient we handle plants in the name of some arbitrary aesthetic, tons of water wasted, many hours spent trimming things to some ideal size that turns out to be terrible for the plant itself, etc. Of course my paranoia doesn't ignore cool pavements either; the reflectivity does bring some mild worries: some skyscrapers are known to cause large amounts of concentrated reflective heat, but those are due to the more mirror-like reflective properties of glass rather than the diffusive matte grey/whites of these pavements. I also worry about visibility, could we end up having a "snow blindness" effect? Would driving be affected as the harsh unnatural dark contrast of a typical road is very easy to spot compared to...everything else. I'm ofcourse aware not all roads are this black but you can't deny bright yellows and whites of road markers on a deep black road would be easier to pick up on than on a greyish road.
  - NumberWangMan 5y ago
    I agree with you on the matter of lawns, but not on street trees. Yes, they require maintenance, but they make a massive difference in the comfort of people walking, which is a big factor in people deciding to walk rather than drive, as well as increasing the general attractiveness of the area to potential residents who might otherwise live in a car dependent suburb of something. When you add up all the benefits, I'd consider street trees to be analogous to brushing your teeth-takes a bit of effort but the cost of not doing it is far greater. This of course applies mostly to areas that are hot for a good portion of the year. And I have the same concerns as you about the reflective pavement.
  - BurningFrog 5y ago
    One logical answer is "Artificial trees". That is, constructed shade structures that provides shade without being unpredictable living things. There are probably real problems with that approach too. What are they?
    - 5y ago
- dec0dedab0de 5y ago
  While I generally agree, you also have to be careful not to go too far in the other direction. My cousin's car was totaled while driving in Philadelphia. A large tree, that was not actively maintained, fell over when the ground was too wet. A foot difference and he would have been killed.
- moonchrome 5y ago
  How do you get trees to avoid destroying concrete/pavement with roots ? We have a lot of old trees around and the pavement around them is bulged, cracked and deformed.
  - clairity 5y ago
    primarily by choosing an appropriate tree that doesn't do that. countersinking the tree can work in some cases too (often with a metal grating around the base of the tree so people don't fall in and hurt themselves). i don't know that you can "fix" the roots once the tree has become well established, without seriously damaging the tree and potentially creating additional hazard.
    - bcrosby95 5y ago
      You also have to be careful of mainlines and turning that into swiss cheese with the root system. Ultimately it takes a fair amount of research to pick the right location and tree.
      - harmmonica 5y ago
        like parent commenter said LA actually has a list of acceptable “street trees” that they’ve approved so they don’t kill the sidewalks. some of the most glorious trees you’ll see here are ficus, but those are not on the list because they do blow away sidewalks, streets, utilities. unbelievable shade trees though that require very little water.
        clairity 5y ago
        i just learned that a huge, grand old tree in my neighborhood is a species of ficus, and indeed, the sidewalk next to it is a buckled, gnarled mess. but i’d rather deal with that problem than harm the tree (it seems like it would be pretty straightforward to build a concrete ramp over the roots, like a mini-bridge).
        5y ago
- wruza 5y ago
  I would add that city people underestimate or simply do not know about the ability of vegetation to cool off its environment. My city has areas (few abandoned plots) with a wild high grass and bushes on them. When it’s hot and you walk nearby, like 2-3m close, it is as if you went from the street to under AC. I don’t know how they do it, but my guess is that photosynthesis is a hell of an endothermic process. And you’re right, modern “city trimming” is just a disgusting non-functional nonsense.
  - cesarb 5y ago
    > [..] it is as if you went from the street to under AC. I don’t know how they do it, but my guess is that photosynthesis [...] My guess would be evapotranspiration, not photosynthesis.
  - compressedgas 5y ago
    It's called transpiration. It is how the plants keep their temperature below the point at which photosynthesis no longer is possible.
    - wruza 5y ago
      TIL. But that means plants move heat somewhere, and not pack it into chemical bonds. This maybe defeats the idea, because these areas are cold because they are rare. If ubiquitous, in a still hot day they would just raise humidity and probably make things worse?
      - peterbraden 5y ago
        Not at all. The areas where they are ubiquitous, which we normally call forests, are still cool.
- ToJans 5y ago
  FYI I've brainstormed on an innovation use case once that would allow citizens to use an app to suggest things like planting trees everywhere using AR etc. When discussing with academics, I was flabbergasted to find out that in street canyons, trees can have a negative effect because they reduce air flow. So, apparently it's not as simple as "just plant some trees"...
  - axelroze 5y ago
    They can also be a hazard as they can crash much easier during a storm, earthquake or hurricane. Especially if they are dry and not alive any more. IMO solving overheated cities is not just more trees but less population density. Less buildings, less concrete, less asphalt. Less generation of heat and pollution in the first place. Less is more essentially.
    - marcus_holmes 5y ago
      Less population density means more transport, though, as the city is so spread out. More cars, more roads, more parking, more infrastructure generally. Smaller, denser cities are more walkable and have more room for parks. Small, single-family buildings are incredibly energy-inefficient. Large 5-story apartment blocks are way more efficient. I moved from Perth, Australia to Berlin, Germany - the difference is astounding. Living in Perth without a car was painful. Living in Berlin without a car is normal. The hot water heating is communal, even in some areas provided for entire city blocks, while every house in Perth has its own reverse-cycle air conditioning setup. High density living is just more efficient per person.
- csomar 5y ago
  > the tree trimmers i see doing this have no idea what they're doing Or maybe they do know what they are doing. Trees need trimming. > not to contemplate consequences or consider other options. Like?
  - Tempest1981 5y ago
    There is a guideline, to not prune more than 15-20% of a tree per season. And less if the tree is struggling. Often urban trees are struggling, but I've seen workers still prune them heavily.
burlesona 5y ago
It's interesting that the effects are so complex and nuanced. I also wonder - they didn't specify - just how reflective these surfaces need to be, and how "bright" they are to look at. I could see glare being a potential safety hazard if the surface is reflective enough, but I'm assuming that any surface rough enough to make good pavement won't be _too_ bad to look at.
- sk2020 5y ago
  I would doubt they went far enough to get meaningful measurements. I think this is just more of the Ivy League enriching itself at the bottomless climate feeding trough. The discovery that light colors absorb less heat isn’t remarkable. I would be embarrassed to see this if I were an MIG alumnus. Statements about replacing all pavement in a metropolitan area (that doesn’t even patch its potholes) are so out of touch that they discredit the whole article. Just replace all that asphalt with concrete filled with, I guess, prismatic beads which would be like staring at the sun? Brilliant! Oh, or use “lighter colored aggregates”? Right. We I never thought to just ask the local geology to rearrange itself a bit so my local quarries can produce a different color product. I’ll give it a go! Several here have made the much more obvious observation: just use plants.
na85 5y ago
This totally nerd-sniped[0] me, and now I'm going down the rabbit hole wondering if there's a business opportunity for generating electricity via the thermoelectric effect[1] and thus literally cooling the pavement by pulling some energy out and putting it to good use. [0] https://xkcd.com/356/ https://xkcd.com/356/ [1] https://en.m.wikipedia.org/wiki/Thermoelectric_generator https://en.m.wikipedia.org/wiki/Thermoelectric_generator
- aaaaaaaaaaab 5y ago
  I’ll save you some time: absolutely not.
  - llukas 5y ago
    https://www.ucdavis.edu/news/anti-solar-cells-photovoltaic-cell-works-night https://www.ucdavis.edu/news/anti-solar-cells-photovoltaic-c... Not pavement but still
  - na85 5y ago
    Why so certain?
    - Nbox9 5y ago
      I’m in the 98% not feasible category for a few reasons. I’m open to new information or arguments, but I can’t see a way over a few very large hurdles. 1. Pavement is a very poor conductor, energy doesn’t move easily through it. 2. The Delta between ambient air temp and pavement temp low. Generating power would most likely include moving energy between the higher temp pavement to the lower temp air and capturing some of it during the transition. This is possible at any delta, but were really talking about a maximum of about 30 degree C temperature delta. 3. There are more efficient ways to generate power. Build wind turbines, solar panels, dams, etc. These are all very good ways of generating power. 4. There are more efficient ways to keep pavement cool. Change the pavement materials, plant trees, build shade sources for the pavement.
      - 5y ago
berikv 5y ago
Why wouldn’t you just plant some trees. You don’t need any fancy pavement if it is below a tree.. European cities are filled with trees to cool the streets below them. Obviously, you’d need smaller streets that fit pedestrians and bicycles instead of massive urban highways for trees to be effective.
- barsonme 5y ago
  US cities have trees, too. One downside, though, is the roots can grow and break up the sidewalk. There are some sidewalks in Seattle that are completely inaccessible to wheelchairs or even folks with walkers.
  - hisyam 5y ago
    You can plant trees that doesn't have pavement-breaking roots.
  - elric 5y ago
    If roots were the biggest obstacle for wheelchair use, I'm sure many a wheelchair user would rejoice. I doubt that's anywhere near the case. Cars parking on the pavement, silly delivery robots, shops with oversized signs, all kinds of rubbish, inaccessibly high kerbs, are likely bigger issues.
- elric 5y ago
  > European cities are filled with trees Bit of an overly broad generalization. Some European cities, sure. But many are desolate and devoid of trees. Many old cities have very narrow streets, which aren't great for trees. A few shrubs, maybe. Wider strees in Belgian cities are generally devoid of trees, because parking spaces are apparently more important -- and we wouldn't want to impede the view of shops and billboards! Whenever urban trees are cut down, there's a bit of protest, but nevertheless it just keeps happening :-(
  - berikv 5y ago
    Turns out your right, the story is much more balanced. This page has data on tree cover per capita, and it isn’t Europe on top US on the bottom : https://datadrivenlab.org/urban/issue-profiles/urban-tree-cover/ https://datadrivenlab.org/urban/issue-profiles/urban-tree-co...
Adrox 5y ago
Well in Portugal (thats is kind of hot) we use limestone or other kind of white stones: https://fotos.web.sapo.io/i/o90119e17/18254271_eGMbD.jpeg https://fotos.web.sapo.io/i/o90119e17/18254271_eGMbD.jpeg Not only is cooler, it looks much better than cement… It can be expensive as it uses a lot of hand labour.
14 5y ago
I am surprise we are not doing more reflective roofs while at it. Black rooftops are so hot.
- dylan604 5y ago
  Aren't all commercial buildings required to be white, at least in the major cities?
mrfusion 5y ago
This would be so amazing for tennis and pickleball courts! People would pay good money for this.
nine_zeros 5y ago
It's not too hard to design good tree lined streets. Here's an example from Mumbai https://bit.ly/3D84CvN https://bit.ly/3D84CvN. It only requires political will. Edit: A POV drive through the same place https://www.youtube.com/watch?v=qgbgu7Pv60A https://www.youtube.com/watch?v=qgbgu7Pv60A
sennight 5y ago
phew, no mention of "solar roadways".
blippage 5y ago
> Countering climate change with cool pavements "Lisa, in this house we obey the laws of thermodynamics" -- Homer Simpson
tempestn 5y ago
I wonder if the increased reflectivity could be a visibility issue for drivers, especially when wet (which can already be an issue with regular asphalt). Certainly sounds good otherwise though.
mixedmath 5y ago
This is good scientific writing. The article discusses some nuance and hints at the complexity of the topic, but presents results in a widely understandable way.

82 points by 35_candelas 5y ago

> “cool pavements” [..] reflect more solar radiation and emit less heat than conventional paving surfaces. Darn, I thought they were going to talk about using heat pipes driven deep into the ground to turn the pavement into a heat sink and was wondering how they were going to get the pavement to conduct heat to the heat pipes. Now I'll never know. ;)

clairity 5y ago

> “Conversely, by reflecting light — called incident radiation — onto nearby buildings, cool pavements can warm structures up, which can increase AC usage in the summer and lower heating demand in the winter.” this is one of the reasons why i'm an advocate for street trees, and urban foliage in general (cuts down both incident and reflective radiation), and why i'm maddened when i see urban trees cut down or cut back (as been happening quite often in my urban neighborhood in LA). the tree trimmers i see doing this have no idea what they're doing, being low-paid laborers paid only to run a chainsaw/trimmer, not to contemplate consequences or consider other options. trees take decades to become effective shade, and minutes to butcher irreparably. that's not to put down cool pavements, which are really cool (haha), but that trees can provide all the same benefits and more, which makes it the better first option, with cool pavements being reserved for where tree shading is difficult or impossible (like roadways and parking lots).

pharmakom 5y ago
I also like urban trees but remember they cost a fortune to maintain! For example, urban trees have to be expertly managed for disease along transit lines.
- frosted-flakes 5y ago
  Why would they cost a fortune to maintain? Apart from leaf collection and end-of-life removal, what costs are associated with street trees?
  - godelski 5y ago
    They require water, which requires irrigation (may not already be in place and of course has logistical problems), trees also root systems can lift and crack sidewalks/pipes/other things, you now have biological contaminants, there's bugs and fungus and things that can spread, and so much more. I'm not saying we shouldn't do this. I really like seeing plant life in cities and I think it really makes a psychological difference (I _love_ living in a city with a lot of green spaces and trees everywhere). But it is nowhere near as simple as placing a tree in the ground and cleaning the leaves.
    - ClumsyPilot 5y ago
      "now have biological contaminants, there's bugs and fungus" Dude, we have rats running around, pigeons nesting and pooping, what biological contaminants?
      - godelski 5y ago
        Just because biological contaminants exist doesn't mean adding more creates more issues. More trees also means more rats and pigeons. What's your argument? That just because we already have a bad thing doesn't mean that a similar bad thing isn't bad? That doesn't make much sense and is a pretty lazy argument.
        ClumsyPilot 5y ago
        Either way, rats and pigeons feed on garbage, they dont eat oak trees. We need to have less takeaway left on the street and garbage bins that are cleaned up on time.
    - Ma8ee 5y ago
      How much irrigation that is needed very much depends on where you are and what kind of tree. After the first few years it take to settle, trees have deep roots and rarely need watering. And I have never heard of trees contribution negatively to "biological contaminants", whatever that means. Rather, trees contribute to a cleaner and healthier environment.
- berikv 5y ago
  The pavement replacement won’t be free either, I suppose. I’ve never heard of a government cutting trees as a cost saving, however I didn’t look for that either. I think that, once trees are there, people will be happy to pay the few dollarcents per year for their maintenance.
harmmonica 5y ago
from one LA resident to another, amen to that. we were just walking down our street this morning and discussing, for the umpteenth time, whether our neighbors would actually be willing to take care of trees if we went out and bought them and planted them. the problem, as other commenters have pointed out, is that they do require upkeep, but since they're living/breathing things the more hardy ones can really be abused and still survive. The question is how do you incentivize the people who benefit from the trees--the residents, businesses, other local stakeholders--to actually maintain them? on our street there are countless trees that were likely planted decades ago, but a lack of care by the residents makes them mere shadows of their potential. and for anyone interested, LA's a great example of how trees provide a return on investment (actual dollar return outside the tremendous ecological benefits). go onto google maps and look at the satellite view. people who have never been here can point out the expensive neighborhoods because they are the greener ones.
- clairity 5y ago
  LA has an woefully underpublicized street (and lawn) tree program, where you can get free trees if you agree to take care of them (which is mostly just periodic watering), so you wouldn't even have to buy them yourself. for street trees on the parkway (the patch of ground between the sidewalk and street), you don't technically even need the permission of the owner, although the owner might not be amenable to watering them then. apartment dwellers (like me) can get trees planted on the parkway just by agreeing to take care of them on behalf of the owner.
  - harmmonica 5y ago
    it's true, that's exactly how we got our street tree, but a) it took an extremely long time to get the tree in the first place and b) the tree itself was rather lackluster, though now we're on year 3 of it and it's... ok. if I knew then what I know now I would've just gotten my own tree (one of the ones on the approved list) to get a nicer tree up front. as for planting the trees without the permission of the resident responsible for that parkway, like I said in that previous comment, it doesn't do much good if the folks don't take care of them. we've also learned the hard way that doing things that seem additive to the hood are not always taken that way by neighbors and can cause conflict. been on the end of that a couple of times already. that said, maybe I'll stop talking about doing this and actually try it and see what folks say.
puffyvolvo 5y ago
While I initially would prefer the idea of more street trees the nagging voice in the back of my head continues to worry about unintended consequences. A big one regarding more trees is more maintenance, you've already pointed out how terrible maintenance can be, and lawns alone are an incredible example of just how inefficient we handle plants in the name of some arbitrary aesthetic, tons of water wasted, many hours spent trimming things to some ideal size that turns out to be terrible for the plant itself, etc. Of course my paranoia doesn't ignore cool pavements either; the reflectivity does bring some mild worries: some skyscrapers are known to cause large amounts of concentrated reflective heat, but those are due to the more mirror-like reflective properties of glass rather than the diffusive matte grey/whites of these pavements. I also worry about visibility, could we end up having a "snow blindness" effect? Would driving be affected as the harsh unnatural dark contrast of a typical road is very easy to spot compared to...everything else. I'm ofcourse aware not all roads are this black but you can't deny bright yellows and whites of road markers on a deep black road would be easier to pick up on than on a greyish road.
- NumberWangMan 5y ago
  I agree with you on the matter of lawns, but not on street trees. Yes, they require maintenance, but they make a massive difference in the comfort of people walking, which is a big factor in people deciding to walk rather than drive, as well as increasing the general attractiveness of the area to potential residents who might otherwise live in a car dependent suburb of something. When you add up all the benefits, I'd consider street trees to be analogous to brushing your teeth-takes a bit of effort but the cost of not doing it is far greater. This of course applies mostly to areas that are hot for a good portion of the year. And I have the same concerns as you about the reflective pavement.
- BurningFrog 5y ago
  One logical answer is "Artificial trees". That is, constructed shade structures that provides shade without being unpredictable living things. There are probably real problems with that approach too. What are they?
  - 5y ago
dec0dedab0de 5y ago
While I generally agree, you also have to be careful not to go too far in the other direction. My cousin's car was totaled while driving in Philadelphia. A large tree, that was not actively maintained, fell over when the ground was too wet. A foot difference and he would have been killed.
moonchrome 5y ago
How do you get trees to avoid destroying concrete/pavement with roots ? We have a lot of old trees around and the pavement around them is bulged, cracked and deformed.
- clairity 5y ago
  primarily by choosing an appropriate tree that doesn't do that. countersinking the tree can work in some cases too (often with a metal grating around the base of the tree so people don't fall in and hurt themselves). i don't know that you can "fix" the roots once the tree has become well established, without seriously damaging the tree and potentially creating additional hazard.
  - bcrosby95 5y ago
    You also have to be careful of mainlines and turning that into swiss cheese with the root system. Ultimately it takes a fair amount of research to pick the right location and tree.
    - harmmonica 5y ago
      like parent commenter said LA actually has a list of acceptable “street trees” that they’ve approved so they don’t kill the sidewalks. some of the most glorious trees you’ll see here are ficus, but those are not on the list because they do blow away sidewalks, streets, utilities. unbelievable shade trees though that require very little water.
      - clairity 5y ago
        i just learned that a huge, grand old tree in my neighborhood is a species of ficus, and indeed, the sidewalk next to it is a buckled, gnarled mess. but i’d rather deal with that problem than harm the tree (it seems like it would be pretty straightforward to build a concrete ramp over the roots, like a mini-bridge).
        5y ago
wruza 5y ago
I would add that city people underestimate or simply do not know about the ability of vegetation to cool off its environment. My city has areas (few abandoned plots) with a wild high grass and bushes on them. When it’s hot and you walk nearby, like 2-3m close, it is as if you went from the street to under AC. I don’t know how they do it, but my guess is that photosynthesis is a hell of an endothermic process. And you’re right, modern “city trimming” is just a disgusting non-functional nonsense.
- cesarb 5y ago
  > [..] it is as if you went from the street to under AC. I don’t know how they do it, but my guess is that photosynthesis [...] My guess would be evapotranspiration, not photosynthesis.
- compressedgas 5y ago
  It's called transpiration. It is how the plants keep their temperature below the point at which photosynthesis no longer is possible.
  - wruza 5y ago
    TIL. But that means plants move heat somewhere, and not pack it into chemical bonds. This maybe defeats the idea, because these areas are cold because they are rare. If ubiquitous, in a still hot day they would just raise humidity and probably make things worse?
    - peterbraden 5y ago
      Not at all. The areas where they are ubiquitous, which we normally call forests, are still cool.
ToJans 5y ago
FYI I've brainstormed on an innovation use case once that would allow citizens to use an app to suggest things like planting trees everywhere using AR etc. When discussing with academics, I was flabbergasted to find out that in street canyons, trees can have a negative effect because they reduce air flow. So, apparently it's not as simple as "just plant some trees"...
- axelroze 5y ago
  They can also be a hazard as they can crash much easier during a storm, earthquake or hurricane. Especially if they are dry and not alive any more. IMO solving overheated cities is not just more trees but less population density. Less buildings, less concrete, less asphalt. Less generation of heat and pollution in the first place. Less is more essentially.
  - marcus_holmes 5y ago
    Less population density means more transport, though, as the city is so spread out. More cars, more roads, more parking, more infrastructure generally. Smaller, denser cities are more walkable and have more room for parks. Small, single-family buildings are incredibly energy-inefficient. Large 5-story apartment blocks are way more efficient. I moved from Perth, Australia to Berlin, Germany - the difference is astounding. Living in Perth without a car was painful. Living in Berlin without a car is normal. The hot water heating is communal, even in some areas provided for entire city blocks, while every house in Perth has its own reverse-cycle air conditioning setup. High density living is just more efficient per person.
csomar 5y ago
> the tree trimmers i see doing this have no idea what they're doing Or maybe they do know what they are doing. Trees need trimming. > not to contemplate consequences or consider other options. Like?
- Tempest1981 5y ago
  There is a guideline, to not prune more than 15-20% of a tree per season. And less if the tree is struggling. Often urban trees are struggling, but I've seen workers still prune them heavily.

burlesona 5y ago

It's interesting that the effects are so complex and nuanced. I also wonder - they didn't specify - just how reflective these surfaces need to be, and how "bright" they are to look at. I could see glare being a potential safety hazard if the surface is reflective enough, but I'm assuming that any surface rough enough to make good pavement won't be _too_ bad to look at.

sk2020 5y ago
I would doubt they went far enough to get meaningful measurements. I think this is just more of the Ivy League enriching itself at the bottomless climate feeding trough. The discovery that light colors absorb less heat isn’t remarkable. I would be embarrassed to see this if I were an MIG alumnus. Statements about replacing all pavement in a metropolitan area (that doesn’t even patch its potholes) are so out of touch that they discredit the whole article. Just replace all that asphalt with concrete filled with, I guess, prismatic beads which would be like staring at the sun? Brilliant! Oh, or use “lighter colored aggregates”? Right. We I never thought to just ask the local geology to rearrange itself a bit so my local quarries can produce a different color product. I’ll give it a go! Several here have made the much more obvious observation: just use plants.

na85 5y ago

This totally nerd-sniped[0] me, and now I'm going down the rabbit hole wondering if there's a business opportunity for generating electricity via the thermoelectric effect[1] and thus literally cooling the pavement by pulling some energy out and putting it to good use. [0] https://xkcd.com/356/ https://xkcd.com/356/ [1] https://en.m.wikipedia.org/wiki/Thermoelectric_generator https://en.m.wikipedia.org/wiki/Thermoelectric_generator

aaaaaaaaaaab 5y ago
I’ll save you some time: absolutely not.
- llukas 5y ago
  https://www.ucdavis.edu/news/anti-solar-cells-photovoltaic-cell-works-night https://www.ucdavis.edu/news/anti-solar-cells-photovoltaic-c... Not pavement but still
- na85 5y ago
  Why so certain?
  - Nbox9 5y ago
    I’m in the 98% not feasible category for a few reasons. I’m open to new information or arguments, but I can’t see a way over a few very large hurdles. 1. Pavement is a very poor conductor, energy doesn’t move easily through it. 2. The Delta between ambient air temp and pavement temp low. Generating power would most likely include moving energy between the higher temp pavement to the lower temp air and capturing some of it during the transition. This is possible at any delta, but were really talking about a maximum of about 30 degree C temperature delta. 3. There are more efficient ways to generate power. Build wind turbines, solar panels, dams, etc. These are all very good ways of generating power. 4. There are more efficient ways to keep pavement cool. Change the pavement materials, plant trees, build shade sources for the pavement.
    - 5y ago

berikv 5y ago

Why wouldn’t you just plant some trees. You don’t need any fancy pavement if it is below a tree.. European cities are filled with trees to cool the streets below them. Obviously, you’d need smaller streets that fit pedestrians and bicycles instead of massive urban highways for trees to be effective.

barsonme 5y ago
US cities have trees, too. One downside, though, is the roots can grow and break up the sidewalk. There are some sidewalks in Seattle that are completely inaccessible to wheelchairs or even folks with walkers.
- hisyam 5y ago
  You can plant trees that doesn't have pavement-breaking roots.
- elric 5y ago
  If roots were the biggest obstacle for wheelchair use, I'm sure many a wheelchair user would rejoice. I doubt that's anywhere near the case. Cars parking on the pavement, silly delivery robots, shops with oversized signs, all kinds of rubbish, inaccessibly high kerbs, are likely bigger issues.
elric 5y ago
> European cities are filled with trees Bit of an overly broad generalization. Some European cities, sure. But many are desolate and devoid of trees. Many old cities have very narrow streets, which aren't great for trees. A few shrubs, maybe. Wider strees in Belgian cities are generally devoid of trees, because parking spaces are apparently more important -- and we wouldn't want to impede the view of shops and billboards! Whenever urban trees are cut down, there's a bit of protest, but nevertheless it just keeps happening :-(
- berikv 5y ago
  Turns out your right, the story is much more balanced. This page has data on tree cover per capita, and it isn’t Europe on top US on the bottom : https://datadrivenlab.org/urban/issue-profiles/urban-tree-cover/ https://datadrivenlab.org/urban/issue-profiles/urban-tree-co...

Adrox 5y ago

Well in Portugal (thats is kind of hot) we use limestone or other kind of white stones: https://fotos.web.sapo.io/i/o90119e17/18254271_eGMbD.jpeg https://fotos.web.sapo.io/i/o90119e17/18254271_eGMbD.jpeg Not only is cooler, it looks much better than cement… It can be expensive as it uses a lot of hand labour.

14 5y ago

I am surprise we are not doing more reflective roofs while at it. Black rooftops are so hot.

dylan604 5y ago
Aren't all commercial buildings required to be white, at least in the major cities?

mrfusion 5y ago

This would be so amazing for tennis and pickleball courts! People would pay good money for this.

nine_zeros 5y ago

It's not too hard to design good tree lined streets. Here's an example from Mumbai https://bit.ly/3D84CvN https://bit.ly/3D84CvN. It only requires political will. Edit: A POV drive through the same place https://www.youtube.com/watch?v=qgbgu7Pv60A https://www.youtube.com/watch?v=qgbgu7Pv60A

sennight 5y ago

phew, no mention of "solar roadways".

blippage 5y ago

> Countering climate change with cool pavements "Lisa, in this house we obey the laws of thermodynamics" -- Homer Simpson

tempestn 5y ago

I wonder if the increased reflectivity could be a visibility issue for drivers, especially when wet (which can already be an issue with regular asphalt). Certainly sounds good otherwise though.

mixedmath 5y ago

This is good scientific writing. The article discusses some nuance and hints at the complexity of the topic, but presents results in a widely understandable way.