Episode 561 Heat Islands and Trees


trees, cities, heat pump, heat, building, heating, suburban areas, cool, energy, planted, cost, asphalt concrete, terms, question, insulation, aspects, urban areas, house, impermeable, air conditioner


Hashem Akbari, Robin Collins, Metta Spencer


In this episode, Metta Spencer has Professor Hashem Akbari, a specialist in heat islands and civil engineering on. Robin Collins a Canadian Pugwash member is also a guest, and he questions Akbari providing a rich discussion. They discuss the concept of heat islands, which refers to cities that have higher temperatures than the surrounding suburban areas. Professor Akbari explains that urban areas, with their dark and impermeable surfaces, absorb more of the sun’s energy, leading to increased temperatures. The term “heat island” is used to describe this phenomenon.

Professor Akbari clarifies that heat islands encompass entire cities rather than small areas. The temperature difference caused by hot surfaces diminishes as one moves higher above the surface. However, the cumulative effect of larger areas of dark surfaces can raise temperatures by a few degrees Celsius.

The discussion then shifts to the strategies for mitigating heat islands and their importance in addressing climate change. With much of the global population living in urban areas and the projected increase in urbanization, the heat island effect becomes a pressing concern. Reducing urban heat is crucial not only for the well-being of city residents but also for mitigating climate change impacts.

The professor highlights various measures to cool cities, emphasizing the significance of changing the color and permeability of surfaces. Dark, impermeable surfaces can be transformed into lighter-colored and more permeable alternatives, such as light-colored roofs and pavements. These changes can be cost-effective and immediately yield benefits in terms of temperature reduction. The concentrated energy utilization in cities is another contributing factor to urban heat, making a transition to more energy-efficient solutions, such as electric vehicles, important.

The discussion then touches upon the role of trees in mitigating heat islands. While planting trees offers multiple benefits, such as energy savings and improved air quality, their economic and maintenance aspects differ from other measures. The cost of planting and maintaining trees varies depending on factors such as individual efforts versus city programs and the scale of implementation. Professor Akbari emphasizes that trees provide additional amenities beyond the cooling effect, making direct comparisons with other measures challenging. The placement of trees is also discussed, noting their interactions with building energy consumption through shading, evapotranspiration, and windbreak effects.

Collins asks Akbari to expand on the importance of insulation and heat pumps in building efficiency and energy consumption. Akbari explains that insulation slows down the escape of heat from inside a building during winter, reducing heating energy consumption. However, during summer, excessive insulation can hinder the natural escape of heat, requiring the use of air conditioning. He emphasizes the need to optimize insulation based on the annual energy utilization of the building, which includes both heating and cooling requirements.

Akbari explains the benefits of using heat pumps in some situations. Heat pumps utilize the reverse process of an air conditioner and can provide more heat energy than the electricity they consume. He recommends using heat pumps instead of resistance heaters for heating buildings, as they are more efficient. However, he notes that the cost of electricity and the initial cost of the heat pump should be considered to justify the switch from resistance heaters to heat pumps. In Canada, where the cost of electricity is relatively low, Akbari considers using heat pumps a favorable option.

Akbari also discusses the concept of cool pavements, which aim to reduce urban heat by reflecting sunlight and reducing heat absorption. He explains various technologies used for cool pavements, such as using light-colored aggregates in asphalt concrete, chemical-based binders and resins, and porous pavements that allow water infiltration and promote cooler surface temperatures. He suggests that the selection of cool pavement technologies should be based on local conditions, cost-effectiveness, and the specific requirements of the area.

Regarding biodiversity and tree selection in urban settings, Akbari highlights the importance of choosing the right trees. While there is no perfect tree that stays mature and trouble-free forever, selecting appropriate tree species is crucial. The cost of removing mature trees can be significant, so careful consideration is necessary. Akbari suggests that the selection of trees should balance individual preferences, the improvement of energy efficiency, and the overall aesthetic appeal of urban environments.

Collins brings up the philosophical question of human intervention versus allowing nature to take its course. Akbari acknowledges the human tendency to modify and shape the environment according to individual preferences, yet he expresses a desire for a collective decision to allow nature to thrive independently. However, he recognizes that human intervention and engineering have left permanent imprints on the environment throughout history. He suggests that finding a balance between human intervention and allowing nature to flourish is a complex and ongoing process.

Overall, Akbari emphasizes the importance of optimizing building efficiency through insulation and heat pumps, implementing cool pavement technologies, and carefully selecting trees in urban settings. He acknowledges the need for human intervention but also advocates for finding a harmonious balance with nature.


The following transcript has been machine-generated using “otter.ai.” Prior to using information from the transcript, please watch the video to catch any obvious errors.

Metta Spencer  00:00

Hi, I’m Metta Spencer. Today we’re going to go to university, Concordia University in Montreal. and we’re going to speak with the professor of civil engineering, buildings and so on. That’s the kind of thing that civil engineers, Hashem Akbari, and we will also be joined by at least my friend Robin Collins in Ottawa, and maybe somebody else who may be a surprise guest. I have to acknowledge that this may be a shorter show than usual, because for the first time in, I think the five years I’ve been doing this, I completely forgot, and had to be, Robin had to call in and get me in gear to do the show, because [inaudible] half an hour, I’d totally forgotten to do it. So I’m apologizing to everybody inside, including our, our viewers who may get shortchanged, because we have to get right onto it. Now, Professor Akbari is a specialist in heat islands. and I know what that is, but I bet not everybody does. So why don’t we start off by having you explain to us Hashem Akbari, what what a heat island is and why we should care?

Hashem Akbari  01:20

Sure, a heat island is a name given to the cities because their temperatures is higher than the suburban area, in a typical Americans and Canadian city, you would find out that the surrounding areas are typically green, the urban areas are mostly made of dark impermeable surfaces, and as a result of that, they absorb more of the sun’s energy and they become hotter than the suburban area. So when you approach from the suburban area to the city, you feel that you are getting into the higher temperatures, higher elevation of temperatures. Hence, the terminology of heat island.

Metta Spencer  02:10

I’m getting from this I’m inferring is that you’re not just saying that, you know, there’s a 20 square foot area of asphalt that’s very hot, but a heat island to you could be a whole city.

Hashem Akbari  02:24

That is correct, that is correct. The signature of the hot surfaces on the air adjacent to the surface at about a meter above the surface would be completely diluted within the air around the, around that area. So you need to have a significantly large area in order to have a significant signature on the air temperature. As an example, if the surface temperature is I would say 150 degrees Fahrenheit, or say 70 degrees Celsius, when you go to the elevation of about 70 centimeters, then you would find out that the temperature is not that high anymore compared to the elevation [highers]. However, if you have a much, much larger area, you will find that at 70 centimeters or a one meter centimeters, the temperature may be one or two or three degrees Celsius warmer.

Metta Spencer  03:33

Okay, Robin, you’re you’re the man who really had some questions about this. So I want to step back and let you pursue this issue.

Robin Collins  03:44

That’s good. That’s great. Hashem. I’ve read a few of your papers, and very clearly, your information on heat islands, and more generally, some of the impacts of trees within cities, and how these impacts affect those heat islands. So I’m hoping to get some detail down. Because there are a few sort of competing strategies on reducing the heat of heat islands, it seems. So I wanted to get your your thoughts on, you know which ones work best, and from my read, let me let me just preface that with one piece of information that came out of one in one of your papers at least, was the important point that while actually the numbers vary, but let’s just let’s just take these two that I that I have that are fairly recent. 56% of the world’s population lives in cities, right? And between 60 and 85% of the world’s energy is consumed within cities, and it’s projected. Sorry did I say 56 now? Yeah, it’s projected that by 2050 68%, up to 68% of the world’s population will be in cities. So we’re going to see a worsening proportionately, proportionately, but also the scale of the problem in cities.

Metta Spencer  05:25

Hold on, why is that worsening? That’s, that’s better? I like city people better than country people. So.

Robin Collins  05:31

So if you have anger towards the city people then maybe, but the point would be that I mean, it’s positive in the sense that if we’re going to address this, they’re all in. They’re all in one place, or to a large extent, but this is a reflection of the migration of populations towards urban areas, and away from very nice is that is that correct? More or less?

Hashem Akbari  05:56

That is correct. It is projected that by the middle of the century, close to 70%, of the world, people would be living in what we would characterize urban areas or suburban areas, rather than rural areas that has, that’s the data that it is mostly provided by United Nations.

Robin Collins  06:20

Okay. So. So the alleviation or the mitigation of some of this temperature is important, not only for the quality of life of people living there, but as some point out, there is a necessity to reduce the heat, other than through air conditioning, for instance. I mean, we can talk about winter heating as well, but let’s just focus on air conditioning that seems to be the focus. So, why is, why is this important in terms of addressing climate change?

Hashem Akbari  07:01

Yeah, I think that let me, let me kind of clarify your question a little bit better. Cities you are getting warmer and then on top of that, there are the global climate change that is happening with what it is happening in the urban areas. So, what people are seeing is the effect of those so called urban heat islands are warming up the cities and at the same time the heating of the globe because of the global warming climate change. And these two factors are cumulative to a certain extent, Surprisingly, they may be linearly cumulative to the level of the changes that we are talking, we are not talking about hundreds of degrees, temperature changes. We are thinking about temperature changes in single digits. and in that scale, typically the effect of the heat island and global warming are cumulative. So, within that, given that the cities are warmer than the suburban areas, one can forecast irrespective of why the city is warmer. One can immediately start focusing on the measures that can cool the cities, and the reason that the cities are warmer, number one is that there are a lot more darker, impermeable surfaces. And these darker, impermeable surfaces within a cycle of 10 to 15 years, or perhaps 20 years can be made into the into the lighter color, and perhaps in a lot of cases not impermeable. And then in addition to that, you don’t have the city formation that exists now, and the chances are that this city formation in terms of the layout would be able to change within the next 30 years is very, very minimal. And then on top of that, you do have the utilization of the energy concentrated utilization of energy in the urban areas that would also contribute to the heating of the cities. Now, focusing on any of these aspects is going to help, in the would be a step in the right direction. And in terms of the reducing the manmade heat, you definitely would like to be able to move away from inefficient cars or internal combustion engines to electric vehicles, and that would significantly improve the the the heat emissions within the city. But the most important element of all of these things is really the making these surfaces in the lighter color in terms of the overall heat balance of the city. And that is, the probably the easiest way to achieve and achieved in the most economical way. And as an example, rooftop, current rooftop which is black now, when it comes to change it, you can change it with the light color rooftop at no incremental costs, and immediately see the benefits. And for pavements, there is a lot more restrictions in terms of how to keep the pavements in light color, but we really do not have to go to extreme light, we can go from a color of a dark asphalt color of the lighter concrete, these are the type of car classes that we have kind of experience throughout the city, when we are driving on the freeways, we will find out that there are high patches of the areas that are concrete, and are in lighter color and we can easily go into that cycle. So these competing elements, really they do not compete, these are things that have to be done in parallel.

Robin Collins  11:42


Hashem Akbari  11:43

And having the resources, whether you can pursue all of them at the same time, or whether you would like to get the low hanging fruits first, which is light color roofs, light color pavements, and then go on to go toward the more, more costlier solutions, these are the ways that we should try to plan for it as the people who are responsible to do something within the cities.

Robin Collins  12:17

Okay, if I can, if I can just jump in there because, because what you just raised their covers two, in my mind, really important aspects of the discussion, in part because our project is about urban trees, right? And, and the goal here isn’t to put urban trees up against albedo effect changes, that is lightening of asphalt and roofs and so on. But just for some scale, and I don’t know if you have those numbers at hand, but there are some who, in recent fairly recent papers, I don’t know which is most up to date anymore, but have, have suggested that planting trees is best bang for the buck. You’re suggesting here that the albedo attention to the albedo effect is best bang for the buck. Because it’s easy, relatively easy to do. Others argue, you know, planting three trees in front of additional trees in front of a house is easy to do. and I know that one of your papers noted that those two impacts combined are probably the greatest impact. And you know, the one of the other ones is, you know, internal water bodies, and that seems to be a lesser one. Can you give us an idea, I mean, it doesn’t matter in an extreme way, which one, what percentages each contribute? But if you can give some indication as to what one does versus the other, and then also, what kind of reduction in temperature does this amount to, and what’s the what are the ramifications of that reduction? It’s kind of a convoluted question.

Hashem Akbari  14:01

I think that’s that’s a very fair and intelligent question and we need to really start to covering up layers of the benefits and the costs associated with each of these measures, and let us focus on trees. Tree plantings can be done by individuals and people are utilizing or installing trees and gardens for the visual and aesthetic benefits and they do not connect that to the reduction of the urban heat island. They enjoy the shade of a tree and they do not connect that to the reduction of the energy consumption in the building, but it may end up to be that way. In their hot day, if you’re sitting there under the shade of a tree and enjoying this cold lemonade, and while your air conditioner is not running in the house, that will definitely have a benefit. So, it does really go as an integral component, which is integrated in the life of the [us] and trying to justify the benefits of the vegetation and trees, only because of the energy savings may be a wrong way to go. And so, however, me to be focusing mostly on the energy benefits and air quality benefits and trying to quantify this, so, there are some aspects of it, which is the benefits or some aspects of it, which is cost. So, a tree being planted by myself starting from a seedling can cause as low as I do not know $1 or $2 to go just buy a seedling and then dig a hole and planted there. Now, then maintenance of that tree becomes an issue, and whether that tree is close to the house or away from the house has been taken care of the house, and how a person is going to value the time that would go to maintain that. If I am maintaining that tree as a joy of the gardening the value of that is the joy that I get is actually the value is negative. So it is making the trees less costly. However, if I ask a professional to come and plant a 10 foot tall tree for me. At the minimum, I should be prepared to spend anything between three to $500. And then if that tree is going to be maintained by a professional over time, when it grows to 50 feet tall, to cutting the branches to removing the debris, and all of these things have to be done by professionals, then the cost aspects of it is a totally different issue. And there is no way that one can justify that level of professional cost by the energy and air quality benefit. So, that is the aspects of the tree. So it the economy covered is totally different from that of the cool roofs that you do it only for the roofing putting a shelter on your roof, and you have the choice of either having a dark color versus a light color. And once you go to a light color, you immediately get the benefits at no costs. So you see that it is, it is not fair to compare trees with cool roofs, because trees is at the same time offer so many other amenities.

Robin Collins  18:12


Hashem Akbari  18:12

That cool roofs, do not. So how are you going to quantify those things? That is really an issue for each urban area, and the priorities that both people both put together in order to justify a program in each urban area?

Robin Collins  18:31

And that also implicates whether, oh, who, who is planting the trees, and who is maintaining them? Is it the individual homeowner? Or is it the city that has a program? and that would, that would change the cost factor? I would imagine and bring it down I would hope I mean, they would be it could scale. It could scale better if it’s not individuals, you know, dealing with arborist companies or, and also where those trees are planted is important as well. Right? And also, you know, whether they’re planted in the right corner of the house, north, south, east or west and and and and that reflects on whether they are going to be useful in the winter versus the summer What can you say anything about that placement?

Hashem Akbari  19:24

Sure, the placement of the trees in terms of the energy aspects of it, trees would interact with the energy consumption of the buildings into primarily three major ways. One of them is shading. Then the second one is through evapotranspiration, and the third one is through the wind shielding. Now, the evapotranspiration is a highly factor of the local climate. If a local climate is highly humid, the impact that we will have to transpiration is not going to be as pronounced as it is in a drier climate, but the shading aspects of it, and will shielding aspects of it is really independent of, are mostly independent of the climate. So, if you plant shade trees on the south west side of the building and therefore, it will be able to interact with or interface with the incoming solar radiation, less energy would be absorbed by your building and if your building is air conditioned, you will need less air conditioning. And if your building is not air conditioned, it is more comfortable the trees also having evergreen trees on the north side of the buildings would be able to break the wind and kind of protect the building from the cold winter breeze and that will probably save some heating energy use during the winter. So, now, remember that in an urban setting my north the north of my building is the south of somebody’s else’s building. So, therefore, it is highly a factor of the local geography and setting in, in urban environment. This type of tree planting would work best in suburban areas and making sure that the trees are being planted in strategic places with respect to individual buildings, while it is not affecting the neighboring buildings.

Robin Collins  22:02

So this, this would this would impact how new housing residential areas are planned also, so that trees planted in one house does don’t block or affect the the houses beside them. So you would design cities or communities that way?

Hashem Akbari  22:23

That is, that is correct. and also you should remember that was remember that at the beginning of the talk, I said that urban setting is a critical factor. You can do that for new development, and how were the existing development in 100 years from now there are going to be a steel constituting 50% of those buildings anyway as it is right now. If you look at most buildings in Canada, you will find out that they are dated back to early 19 hundred’s.

Robin Collins  22:57

Right. So, am I in my correct in thinking also comparing shading and sheltering that is wind block versus shading in the summer, wind block in the winter shading the summer that the impact of shading in the summer is significantly greater than the impact of trees doing sheltering in the winter? So I mean, if you’ve got windy winters and hot, hot summers, you’re better off if you only have one choice to focus on the hot summers than on the cold, windy winters. Is that correct? Or is it debatable?

Hashem Akbari  23:39

In some climates in Canada’s climate? I have to argue perhaps that’s not correct.

Robin Collins  23:47


Hashem Akbari  23:48

Because Canada’s climate, the summer is fairly short and the heating, cooling energy consumption. Shade trees can to a certain extent minimize it, and perhaps even eliminated with when it is combined with the cool roofs or other measures. But since the cooling energy use is typically a fraction of the heating, energy use. Having cold buildings shielded from the cold wind, particularly in suburban areas setting would probably have a more pronounced effect in terms of the actual saving of kilowatt hours.

Robin Collins  24:38

Very interesting.

Hashem Akbari  24:41

That might be what your conclusion your your summary was coming. That may not be the case in a place such as Washington DC.

Robin Collins  24:50

Right, right. Right. Yeah. and some of the studies are are in US cities are hot in California. Did that I mean, there were three or four cities that I’ve seen the reports on, and they were all in the US. So if you could comment a little bit on some of the other options for, for reducing heat in cities, and how they might look compared on a in a scaling way compared to the albedo applications and the tree applications. And a couple of them are that I have, if you have others, please mention them too. Our installation of heat pumps to replace furnaces, and actually I don’t, I don’t know exactly how these work but a heat pump replacement as a as a as an improvement over existing installations. And also adding insulation to older houses. I mean, we assume that newer houses will have everything done properly. We maybe, we shouldn’t assume that but let’s for the sake of argument do that. So older houses are what we’re talking about in terms of improving their resilience to heat and cold. So, to what extent would let’s say adding insulation to your house be a major benefit compared to other options and as well as a heat pump?

Hashem Akbari  26:22

I think that the [inaudible] there is a clarification with respect to heat pumps that I come back to later, but let us talk about the insulation insulation during the winter, the house is always warmer than the outside. So, if you add insulation, it would slow down the escape of the heat from inside to outside and therefore, it would reduce your heating energy consumption. During the summer, there are times of the day and transitional [inaudible], there are some times of the day that inside is warmer than the outside for instance, each side is middle of the day it is 78 degree Fahrenheit or let us say 28 degrees Celsius or 26 degrees Celsius outside is 20 degrees Celsius. Now, in order to keep the house cool, you can open the window, But if you forgot to open the window, if you have more insulation on the walls and the roof, the heat would not be able to naturally escape the building and you need air conditioning.

Robin Collins  27:42

Right right.

Hashem Akbari  27:43

So, that is in commercial buildings, they have a device which is called economizer which allows fresh air coming in from outside and mixed with the inside and by that way cooled the building rather than utilize, fully utilizing the air conditioner. So, you therefore when you’re designing insulation for a building, you need to optimize it on the annual energy utilization of the building which constitutes both heating and cooling. That is hugely a function of the climate in, in Canada, obviously, having the higher insulation is the best, but in some of the coastal areas of Canada such as in Vancouver area, which a lot of newer aircon buildings are having air conditioner, if you have insulation, it may not be helpful during the summer. So, coming back to the heat pump, heat pump, or a furnace. A furnace uses some source of energy to heat your building. This furnace can easily be a gas heater, or air resistance electric heater. A heat pump is a device which is a reverse of an air conditioner, which is utilizing electricity and providing heat into your building by typically a factor of two of more energy that is being used by the electricity. For instance, if you use a resistance heater, for every one kilowatt hour of electricity that you use, you provide one kilowatt hour of heating to your room. If you use a heat pump, for one kilowatt hour of electricity you use, you can provide up to three kilowatt hours of heat into your room. So what it does, it pumps heat from the outside cold air inside your building. So I am a little bit puzzled why in your question, you brought the terminology of insulation and heat pump together? Because these are two different aspects of the building operational efficiency, and they work differently and in parallel.

Robin Collins  30:44

So they’re not in conflict necessarily, though, or…

Hashem Akbari  30:48

To the extent that I understand your question, the answer is no.

Robin Collins  30:51

Yeah. Okay. Yeah, I mean, my question was more, should people switch to heat pumps from what they have now? And I’m not I’m not presupposing that they would or would not increase the insulation? Because, you know, if you combine these two elements, there’s probably a best option in that combination. and so I’m, it’s an open ended question.

Hashem Akbari  31:19

I, to me, the answer is crystal clear, and let me also make crystal clear to everybody. If you’re using electricity to heat your building, using a heat pump would be more efficient. There is a big however, if the cost of electricity into your building is zero, you do not spend the money to buy a heat pump. So, in order to justify the incremental cost of a heat pump to a resistance heater, you need to have a balance between the cost of the electricity realisation and the cost of initial costs of the heat pump. In Canada with a typical home needing perhaps five to 10,000 kilowatt hours of heating during the winter season, and the cost of the electricity to be typically between six cents to 10 cents a kilowatt hour having a heat pump is a no brainer.

Robin Collins  32:40


Hashem Akbari  32:41

Go and borrow the money to individual houses if you already do not have it installed a heat pump. And most new constructions in Canada I have noted that they have a heat pump. In apartment buildings they have a heat pump that it is water based on bit is providing the heat from the well underneath the buildings into the, into the building with the heat pump. So, there are there are quite a few ways of going to a heat pump it is crystal clear. Now having that is if you are having electricity as the source of your heating, if you are having gas as a source of a heating, then you are being faced with two with one optimization question which has two parts. The cost of gas is typically lower than the cost of electricity. So if you switch from gas to electricity for heating, there is an additional incremental costs, and on top of that the cost of the heat pump compared to a furnace, a gas furnace.

Robin Collins  33:56

Right. Yeah, I mean, I think there’s there has to be a calculation here on the projection as to whether people will be allowed to use gas let, let alone the cost of replacing but that’s a that’s a good point that you made. So I have one more question about mechanisms for cooling cities, and then I have two general questions that I’d be interested in your responses to. So I’ll just start with the first and you’ve written a bit about cool pavements. Can you, can you describe what those are and the kind of the scale of impact that they might have?

Hashem Akbari  34:36

First, I start with an anecdote. You know, cooling the cities is important, but making a cooling environment for the citizens is a lot more important. So having shade trees would protect people from the direct sun and provide a more comfortable environment for them. So even if the city as a whole is not cool, so shade trees play a significant role in that space. Now for the cool pavements, the technologies are quiet diverse. Number one. If you look at the asphalt concrete, there are two terminologies, cement concrete and asphalt concrete. For short, we call we call them one of them as asphalt, the other we call them as concrete, but actually it is cement concrete or asphalt concrete. For an asphalt concrete, it is a mix of a binder, which is typically asphalt and aggregates. If you have availability of local resources with the light color aggregates, if you mix these light color aggregates, even in the dark binder, after about six months, the top layer of the aggregates are going to be dropped off, and the aggregates would show itself. and therefore you would have a lighter color asphalt concrete. So the other option is rather than using asphaltic base binder, you’re there you can use chemical base binders, and resins for these binders. That is another technology that they use, there’s a third technology that they use rather than hot mixing asphalt, which is mixing of the aggregates with the binder and then laying them on the ground. There is a technology which is known as [ship] steel, what [ship] steel does is sprays a layer of the binder on the surface, and then sprays on top of that the aggregates and then rolls the aggregates into the binder. So by this way, the aggregates would be light color from the first day. and of course, there is a vacuum that comes in later on and removes the loose aggregates. Each of these technologies that I said would apply in different settings and environment. and then on top of that, you do have porous pavements. porous pavements are extremely, extremely good for areas that have plenty of water. And that have large areas of the parking lots or large area of low, low traffic, roads, such as alleys. In that areas so rather than having totally impermeable surface, you do have blocks of concrete or some other sub structure, that grass would grow through them. So that way, you can keep also the environment very cool. So this is these are a series of technologies for the current asphalt concrete. And then you don’t have the cement concrete that you can have the choice of the light color aggregates in the cement, again, using the white or light colored cement versus dark color cements, and you see a variety of these options available on your eyes when you are driving on freeways.

Robin Collins  38:38

Right? Right? I mean, it seems it seems that with with that latter option. I mean, there’s the problem of cement concrete and co2 that we know about. But there’s I mean, you have to you have to weigh that I suppose against the lighter color, that is the lighter shading that is reflecting lights when albedo effect, and also the longevity of con, of that versus ashphalt and the process of reinstalling or whatever. What, what, what’s the balance here? I mean, I know it’s hard to say because we’re talking about different climates and cracking and all this but are there some general things you can say about that?

Hashem Akbari  39:21

Yeah, I would answer your questions in two parts. One part is the existing reality in some cities in United States, such as Houston, Utah, Utah, Salt Lake City, Utah, you’d find out concrete is being preferred, and that’s what they do. And they have justified that concrete is better for their environment and with more economical in terms of the lifecycle operation. Now whether in that life cycle operation, they have accounted for the co2 emission with the cement production. I am not quite sure, but that is the reality, that’s what they do. In some other areas, they do not do that. The, my humble view is that for both of these technologies, rather than they compete with each other, there are options available at incremental costs, very minimal incremental costs, we should explore those options first, and then get to the options or whether one is better than the other. And remember that in some areas, concretes are the only solution for immediate patches. asphalt concrete would provide a more plausible solution. So it is it is something that one has to do a little bit of investigation in each area, and then develop a protocol and follow that protocol seriously, for a decade or so, get fit back to that, update it as it is needed. But it is something that you really need to have some good leadership within the city in order, in order to make effective program.

Robin Collins  41:28

Very good. So I have, I’m going to combine the last two questions, if I might, and this is more, there’s a bit of a philosophy, philosophical question here. But in there’s a biological question, too. So in that we’re generally speaking, it’s focusing on the tree aspect the planting tree aspect, which, which in the context of all you’ve described, gives us a lot of good thinking in terms of, you know, priorities, and so on. But as you said, they’re not necessarily in competition with one another. They’re complementary and in parallel, but this the question here about in terms of planting trees, and it kind of it comes quickly to mind that we had a tree that that fell, I mean, it also wasn’t an indigenous tree, it collapsed outside our house, and the city replaced it with another tree, which is also not indigenous, it was a Japanese tree of some sort, I can’t remember what iit’s called, but it’s definitely not originally from here. And so you know, people raise their eyebrows, it’s not indigenous, what about biodiversity? So I want that that question, if you can, if you can give some thoughts on it. I mean, in terms of the current crisis, how important is the bio, biodiversity question for urban trees I mean, specifically here, The, the broader question of, of, you know, trees in nature, and more broadly speaking in the boreal forest, and so on. That’s, I think that’s a separate question. So how important is biodiversity in terms of selection of trees in urban settings? And secondly, you know, one of the criticisms of those of us who think that we’re in an urgent situation, is that we should let nature provide and let nature do its thing. and we should minimize human interactions or it interventions. In we’re talking about engineering here, and I’m talking to a civil engineer. So clearly, I think you you, you’ve made clear what you think is important. But is there some, is there something here about that, that you, do you ever consider, you know, let nature provide let’s say, at least in the suburbs, in terms of of trees growing back on their own, versus planting trees? So those two mean that they’re quite different questions, but what are your thoughts?

Hashem Akbari  44:09

On the first part, choosing the right trees are extremely important. You in certain cases, do an urban tree, you want an urban tree that grows to a mature level, and it stays in that way forever. But such a tree doesn’t exist. However, there are other options, which comes fairly close to that. and one has to consider that. The cost of a tree planting, if it is done even by an individual initially, may be minimum, but the cost of the removal of a dead or troubling three, when it is the totally mature would go in terms of the 1000s of dollars. So here we are now, are no longer talking about, we are no longer talking, we are talking about the improvement in the energy aspects of the society or comfort, we are really talking about our individual preference of the way that we would like to live. And naturally, having an urban setting that are mostly, in my humble view, ugly, impermeable surfaces, having some level of comfort of vegetation, gardens has been something that we have been doing for ages. And I think that we would continue doing it one way or the other. and we would learn our way, and those people who are better off spends money every year of changing their garden, putting new plants and letting the design the way that they want to do. Now, going back to the second part of it, though, letting, the letting the environment to take over of it, and we have been intrusive in all aspects of the society, I would like to see the day that we would come to a conclusion, a collective conclusion that we would let an environment to go and grow all by itself. And that may be to a certain extent, an idealistic thinking, but whether it was happening or not, from the first day that the human have started to grow in this planet, of what they have done is that they made permanent impression on the surfaces. So if you look at what we are doing, from the day that we born to the day that we die, we move things from one place to the other one place to the other, and just look around, anything that around you. and you will find that that none of those things are put together by the nature, the human had done that. You’re reading your books, your shelves, your elevator, the oxygen that we breathe, the air conditioner, the fuel that we burn. So these are all aspects of the things that we are doing. and obviously, we have to come to an equilibrium one time or the other. Otherwise, the nature would take care of that for us, it would make that equilibrium for us, such as the ice ages, that you know, are totally changed the way that we have been, or the human have been living before that. So I am not willing to, you know, participate into such a kind of fictional discussions, that I’m a realistic person, I always think, what is the problem out there, and what is the thing that I can do to solve it right now? And I this time I see that you know, urban trees can be significantly an element of the improved environment in an urban setting for the citizens. And therefore, we’ve got to find out ways to overcome the problems that it may come and then try to monetize it or digest it and try to make a better living for ourselves.

Robin Collins  48:58

Very good, and there is that that urgency question, how quickly we have to turn things around, and it would seem unlikely that stepping back and letting nature take its course wouldn’t be quick enough considering what humans have done to this point to the environment.

Hashem Akbari  49:17

Also, also remember that the aspects of the climate change have been accelerating the process of the nature. Trees have been migrating north or south based on the gradual changes in the climate. And now if that change is accelerated significantly, trees cannot migrate that fast. So if we allow the nature to take care of that, of all the problems that we have created and the solutions may not be what we would like to see.

Robin Collins  50:06

Thank you.

Metta Spencer  50:07

Thank you, you know, this has, it’s brilliant. It’s really, this is just really wonderful. I didn’t anticipate how interesting this conversation was going to be it isn’t a conversation, you’ve given us a whole, a whole bunch of things to think about and to learn. So I’m just delighted with it, and thank you. and I’m glad that Robin said we need more of this guy. So he was right. Thank you, Professor Akbari and I hope we haven’t held you up too much. Go to your next appointment. Thank you.

Hashem Akbari  50:43

Thank you very much. It is a little bit more than that than I have already told them that I may be late for, by half an hour so I try to be accomodating.

Metta Spencer  50:53

It’s been wonderful, appreciate it.

Hashem Akbari  50:55

Certainly was a pleasure to join this discussion. and I’m always there, and we got to make it happen. We have created the problems, we are the solution.

Metta Spencer  51:06

We are the solution. Thank you. Bye Bye.

Hashem Akbari  51:09

Take care, bye-bye.

Metta Spencer  51:10

Project Save the World produces these forums, and this is episode 561. Watch them or listen to them as audio podcasts on our website tosavetheworld.ca You can share information there about six global issues too. To find a particular talk show it or its title or episode number in the search bar or the name of one of the guest speakers. Project Save the World also produces a quarterly online publication Peace Magazine, you can subscribe for $20 Canadian per year. Just go to pressreader.com on your browser and enter the word peace in the search bar and you will see buttons to click to subscribe. and finally, I want to thank the viewers who like our forums and help us keep the series going by sponsoring us on Patreon.


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