Thank you for being part of 100 Climate Conversations. This is number 17 of 100 conversations happening every Friday. The series presents 100 visionary Australians that are taking positive action to respond to the most critical issue of our time, climate change. Broadcasting today from the Boiler Hall here at the Powerhouse museum, the Powerhouse acknowledges the Traditional Custodians of the ancestral lands upon which their museums are situated. We are of course, coming to you from the land of the Gadigal People, of the Eora Nation here and we recognise their Elders past, present and future.

I’m Craig Reucassel. I’ll be your host today. Thanks for coming along. Dr Sebastian Pfautsch is a tree physiologist who studies urban heat and microclimates in Sydney, which is experiencing higher temperatures and more frequent and longer lasting heatwaves that are predicted to become even more severe. He leads several projects focused on reducing urban heat across Sydney’s parks, schools, playgrounds, public spaces and neighbourhoods. Welcome, Sebastian. Lovely to have you here. Now I need to start, let’s go back to before you got on to urban heat, you worked as a forester and an ecologist in Europe and Australia. Can you tell us about your kind of background? I am fascinated by tree physiologists and where this came together.

I, as a kid was very sick. I grew up in Frankfurt, in Germany, early 70s. Air pollution was a thing. I had big problems with breathing and so my parents got us a holiday home outside of Frankfurt in a forested area. So that was my contact every weekend, every holidays, any time we could escape the city, I was actually driving the bike with my brother through the forests and learnt all the mushrooms from my granddad and so on. So, I very early on had a very deep connection to forest, I would say. That got lost, I got a bit of a wild teenagehood in Frankfurt. Skateboarding and graffiti and all of that got me away from the forest. I became an interior designer and window dresser, believe it or not. But I needed to do something else. And long story short, it ended up being forest science and forest management. And I studied that in Germany and in the end with that study, at first I had a master and then I had a PhD all of these research projects that I did, I did in Australia.

And then you move to Australia, which obviously has very different climate conditions, very different flora and fauna in comparison to Europe. What were your first thoughts when you came and started working in Australia?

Well, one thing that was really different, of course, was that there were eucalyptus trees everywhere and they just looked different and the forest smells different. There’s this herbal smell in the forest, tangy, that we don’t have. Also, of course, I didn’t know any species. I learned all my forestry knowledge around with the Latin names and species based on what is in Europe, and Europe because of the ice ages went through, erased all of our diversity. And then we got, about 10,000 years back, where we have our forests now, where you have maybe 12 to 15 species, it’s relatively easy. I come to Australia and only the eucalyptus already had 800 species, the acacias had 1200. I had no idea.

So you got captured by Australia, but what led you from the kind of forestry into looking at urban heat? You know, what lured you from staying entirely surrounded by bush back to the city?

A very practical decision about, can I continue working with trees or do I have to shift my field? That was about, that crunch point I reached about five years ago. In Australia, we were leading the world with forest science into the 90s and early 2000s. From then on, we saw in forestry, a rapid decline of R and D investment from industry and also from government. In – I can’t recall, I think it was 2014-15 – the CSIRO section for forestry was dismantled. Forestry in Tasmania stopped entirely and all the forestry companies that would traditionally invest into R and D, which is of course money that we need to do the research to inform their practices, was drying up, so there was really no funding available to continue with research in natural ecosystems, ie, forests. And I needed to make that decision very practically. I need to fill the fridge, I have a mortgage, so what do I do? And along came this job where I could still work with trees but shift from the natural ecosystems completely into manmade urban space.

And in a sense, part of what you are doing is trying to bring the forests back to the city. I mean, that’s really the core of what you kind of do in a way.

In a way. I also really had to admit, because of tree physiology, I understand how trees work and there are limits to what trees can actually deliver when it is around urban cooling and the function of actual cooling in our cities. So, I had to broaden my research program a lot into different spaces. I work in playgrounds now, I work in schools, I start putting reflective paints on roads and car parks. I very quickly had to expand from trees into what else can we do to keep our city cool or to make it cool?

Well, let’s start with the problem itself. So urban heat is increasing, obviously climate change is increasing the heat of our Earth. What kind of flow on effects is that having in our urban areas? Particularly you look at urban heat in Western Sydney. What kind of levels of heat are we seeing? Are they increasing? What are you able to monitor?

When we talk about urban heat, from a science perspective we have to be a little bit more precise because heat is everything. You can even have a heat wave in winter, it does exist, meteorologically. So, what are we trying to actually do in urban space? So, we have to refine our language and say, ‘Okay, with my intervention, I have a problem with nighttime air temperature. What can I do to reduce summer nighttime air temperature?’ Because we know during heatwaves when we are not cooling down our city, we have two or three of those hot nights, people don’t recover from the heat stress during the day, hospitalisation rates in the ERs go up. This is when the people start keeling over because the body can’t recover from the heat during the day. So, we have a very specific temperature metric where we say, now let’s work on solutions for reducing nighttime air temperature.

When we talk about urban heat in general, of course we have two processes that affect the city, the Sydney Basin, one is urban densification. We are reducing greenspace open space that is available inside the city and put more hard infrastructure in buildings, multistorey buildings and so on. At the fringe zone we see expansion of the city where we transform former agricultural peri-urban land into new suburbs, our urban sprawl at the urban fringe. And these two processes affect our microclimate in different ways. We’re basically taking cooling out of the existing city and because we are transforming the land on the fringes of our city, and this is the special case of Western Sydney, we are adding in an already hot environment a lot of infrastructure that will make it even hotter.

What’s interesting, you talk about microclimates because I mean, you’ll often if you watch the weather on the news, you’ll see that Western Sydney is often a lot warmer on hot days than coastal Sydney. Temperatures go up, people end up in hospital. Who is affected by these heat waves? Who is at risk? And how big is that risk?

What we normally hear is for the vulnerable population, the old, the very young, children can’t sweat, toddlers can’t sweat. They haven’t developed that kind of heat exchange yet, they only exchange convectively, so they overheat very quickly once you get past 37.6 [degrees] which is their core temperature. So these are normally named very old, very young but there are also lots of people out there with medical conditions. They take medication where the body stops sweating, some people are bound to the bed. Then there is a group that rarely gets mentioned, but this is the group that really has an impact on our economy. And the New South Wales Government has produced an intergenerational report that estimated the economic losses from heatwaves that are expected, it’s the outdoor workers. Outdoor workers are producing our roads, building our infrastructure, houses, homes.

I’ve got a dataset from South Western Sydney where I analysed thousands, hundreds of thousands of records for hospitalisation against age and temperature from the outdoors and it clearly shows that the group that presents the most is the one between 15 and 30, male. These are the ones that work outdoors, that’s the cohort of the guys with fluoro shirts and a helmet and the long pants and steel-capped boots that have to keep working because, A: they don’t have the disposable income to just walk away from the job and say, ‘I don’t want to work in this heat. I’ll get another job.’ They probably don’t have their supervisors actually realising how dangerous it is to keep working at these high temperatures and they cannot afford to, in the end, find different ways of income more broadly. That’s why you cover this really broad spectrum, and it affects people that are working outdoors in Western Sydney the most. It’s bizarre that it collides with so many factors around urban heat.

Well, now, over the past few years, you’ve done a lot of work with councils in Western Sydney to try and control the heat there, to try and look at some of these problems. One of the projects was re-imagining a very hot playground in Merrylands and trying to turn that into a climate safe playground. How did you come about this project?

So that was really an interesting one because it again combined many things. Why a playground? Kids already, and we know that from international research, spend more and more time indoors. Screen time is getting longer and longer per day. Outdoor play is extremely important, we know that from educational research and also from health research. It is extremely important for kids to develop physical fitness, become risk aware, have cognitive capacity to deal with problems, be compassionate about nature and your fellow human beings. So, there are lots of levels of why outdoor play is so important.

I keep saying, ‘How can we expect to have the next five generations saving this planet if they don’t even have a connection to nature that was established early on? How can we expect them to be passionate about nature in the future?’ So, there’s all this aspect of children’s development and then we have climate change. And we already see that the window, so the opportunity for outdoor play because of our hotter summers, is becoming smaller and smaller and smaller. And that of course, on top of screen time becoming longer and longer and longer, you really need to start designing playgrounds in a way that is attractive for parents. So, it’s not just that the kids play in great equipment, shaded, and their parents sit on the sidelines in the blazing sun because they will only stay for 10 minutes, then they’re too hot. But we really have to look at playgrounds as places where we invest in the future of our community.

This particular playground that you were doing the work on, tell me, how hot was this kind of microclimate before you started fixing it?

It had zero shade. It had dark bark mulch. It had dark blue rubber surfaces. It had a little dolphin made out of some plastic that was on the ground, so for kids to sit on. The bark mulch in the summer was 80 degrees surface temperature Celsius. The rubber material that was about 90 degrees. So, I’ve got an instrument that can measure how hot it actually feels like, so it’s the feels-like temperature because it takes into account radiation, air temperature, wind speeds and the radiant heat load that you get. I was there during the heat wave in 2020, in January and I measured 65 degrees, feels-like temperature, on this particular spot which is a spinner for a wheelchair because it’s an inclusive playground. Can you imagine being there in a wheelchair and feeling like 65 degrees.

65 degrees.

And the little dolphin, the top of it was about 95 degrees hot. So, you would definitely burn the child if you put it there and it puts its hands down, it’s a hazard. We changed all that. We introduced shade, we introduced trees, so we planted additional trees strategically in the north and the west of the playground to give us canopy over time. And we had industry partners collaborating with us because they got also passionate about changing this playground as a demonstration site for what we call Australia’s first UV Smart Cool Playground in Western Sydney.

They gave us as in-kind contribution, a whole shade dome where we strategically put shade sails up again in the north and the west that are completely blocking UV and are lighter on the southern and eastern side. So, we tested then with our instruments, how does UV actually get blocked in this playground and how effective are we eliminating radiant heat? And I can tell you that the surface that before was 80 degrees is now at air temperature. So when you have a 35 degrees day, the shade quality is so high that the radiant heat is completely cancelled from this kind of surface. The same with a blue rubber surface, completely cancelled out. And it’s basically surface temperature equals air temperature, you’re not getting any additional radiant heat load.

We also installed drinking water because we thought it was very important when you want to play active, you also need to stay hydrated. So, it was really a weaving together of several different aspects. The surface has a light colour now and it never had that before, the bark mulch was dark. So we brought all of these elements together to really demonstrate what’s possible. And the structure, the shade structure, is a modular structure that once the trees grow up, we can take to the next playground, adjust to the next playground, and therefore have a sustainable use of the materials that were created for this particular project.

It’s great. It’s great. And did it work? Did you see more kids coming back to the playground?

Absolutely. I even had, for that project, I did research afterwards to capture what we actually achieved. I had trouble to protect my instruments after the shade was there because there were always people.

One of the things you did there is you changed the colour of the surfaces there. How big an impact has that had? There seems to be a lot more discussion nowadays about the colour of your asphalt or the colour of roof materials and that. How big an impact does that have on heat and cooling?

It is hugely important. The colour of, let’s say, a rubber surface in a playground, depending on the material of the rubber itself because there are different plastics available in the industry. The cheapest, of course, is the hottest, it’s made from recycled car tyres that just get coated with colour pigments. And then you have materials that are this colour through and through. So, with wear time, you would lose the colour cover, let’s say, of a dark blue, that is cheap, and the black comes out, whereas over time the other plastic stays dark blue. You can have differences in surface temperature of more than 20 degrees, just depending on the material and the colour from the hottest to the coolest unshaded material. Once you introduce shade, no problem anymore. And of course, you also eradicate the problem of being exposed to UV, which we know when you’re exposed to UV as a child, overexposed I should say, you have a much greater chance to develop skin cancer later in life. So, there’s another aspect to that kind of heat protection.

Since the Merrylands playground, you’ve just now set your attention to another common part of our environment, and that’s the car parks. The research has found there are over six kilometres squared of asphalt in Western Sydney, a figure that equates to around 840 soccer fields. Why have you chosen to focus on car parks?

It’s the lowest hanging fruit. We have them. With those six square kilometres, only 1 per cent is shaded, we measured that. I mean, can you imagine six square kilometres of just black, flat surface without anything? Of course, even if we switched to EV, we still have a very large use of individual transporting people because they’re all car dependent. They live in suburbs where you have no public transport or very bad public transport, and they are about 60 kilometres away from where they work. Even if they can switch, if they can afford to switch to EVs, they will still have to use their car, which means you still need car parks. So, the car parks are not going away even if we see a switch from combustion to electric. So, car parks are with us.

We also looked into the increase of car park space throughout all of Western Sydney with the population increase. And of course, when we build these new suburbs, they’re not just built for now, they’re built for the next 20 or 30 years, so you build much more capacity into car parks so that they can deal around the shopping centres or the IKEAs or wherever you go commuting, car parks next to train stations, they’re completely oversize now and deprived of shade. So what happens at these car parks is that a lot of heat gets absorbed and stored, a proportion of that gets re-radiated into the environment immediately. That’s when you walk over a car park, you really feel hot, that’s this feels-like temperature again.

So, take a hospital car park, you now have people arriving at a hospital that need help for whatever reason, they first have to walk 200 metres through an area that feels like 55 degrees, not very healthy. So, there’s a risk here. When you think of the commuter car park, let’s just take that one, I did some work, for example, on the big car park from the new Sydney Zoo. That is like a commuter car park. You have people coming, they go away, they visit the zoo, they come back, they drive away. Well, the introduction of this car park meant that air temperature increased around the car park everywhere which of course, leaves nature warmer. This affects food chains, this affects various aspects of how these ecosystems around, that are still there, actually work. It affects plant life and so on and so forth. So, there is an ongoing impact that of course, scales across the landscape. When you think of these six square kilometres, of course, not in one spot, they’re everywhere. And the cumulative heat that you generate leads to more urban warming.

It’s interesting isn’t it because we talk a lot about the macro effect of burning fossil fuels as creating warming. But even some of these micro-decisions we make in our communities actually also increases the heat there. So, what can we do about this? Are you painting car parks? What can you do to actually fix this?

You could put reflective coatings on car parks, and we did a project with three councils where suddenly councils could actually work together. That was great to see because heat doesn’t have a boundary, it doesn’t care if it’s one council or the other, it works across the boundary, so they have to work together. When you want to change heat in car parks, I think it’s, that’s why I say it’s the lowest hanging fruit, it’s relatively simple because you can just do an occupation assessment over a certain amount of time. After that, you know that you probably oversized your car park, let’s say for, ten spaces. You can now strategically select the ten spaces where you rip the asphalt up and you actually plant big canopy trees. It will provide you with shade that has cooling benefits on the ground and also in the air, you lower the air temperature.

When you start building the car parks you don’t need to use black asphalt, you could use a pervious material of a lighter colour, concrete pavers. So, you have water infiltration and therefore you have evaporation from it. You have a lighter colour, you store less heat in this material. So, there are various design options that are not hard to do because you’re building the car park anyway, just be a bit smarter about it.

So have your experiments with car parks, the greening car parks, has that worked? Has it reduced temperatures? Has it solved the problem?

Well, I now finally have the okay, we have an innovation project with Cumberland Council where we also did the playground. They are very interested in this kind of innovation. They have a relatively low socio-economic throughout the population of Cumberland. They know their cancer rates, they know their heat problem because they don’t have a lot of canopy. So, they are interested in cooling projects.

We’ve got one now where we go to Holroyd Gardens, there’s a big car park for the people that come and visit or have their weddings at Holroyd Gardens and we will build a prototype where we use trellises to train fast growing vines to overgrow the entire car park because they decided it’s not worth damaging the car park surface, let’s look at other options. And so we designed with them, a structure that will be put in and I will do all the measurements of course, to then say, ‘Well, surface temperature, air temperature was reduced by X compared to an unshaded car park. And again, take people to the car park and show them how it can be done without massive investment. This is something that we do, again it’s modular, so you can replicate our design in any other car park and use fast growing vines.

I often feel for scientists because I feel like scientists have been telling us for decades and decades, ‘We’ve got to solve this problem, we’ve got to address this problem of climate change’ and yet have been ignored for so long. How do you feel? Do you feel like you are being listened to more now, that science is being at least adopted and listened to more than it was being years ago?

I don’t want to speak for every scientist. I can speak for myself and I can tell you in the 15 years that I worked on fundamental plant science, I never had anywhere near the impact with media, with the public, with politicians that I now have in the past five years, and even more so in the past three years, that I have now working on cooling and green infrastructure and everything else that we can do. So, there is a change, I can see that because people start to understand. We see it mainstreaming, which is great because it means at some point, I have to look for different work because the work that I’m doing now, I don’t need to do anymore because things have changed that much. That’s really where I’m heading.

I think you’re right that there seems to be a lot more understanding in the community. And obviously there’s a big difference between being told in 1980 this is going to happen in 20 years or 30, 40 years. There’s a big difference between being told that and now experiencing it now, so people really are responding and it’s great to hear that we have solutions there, that they are being on taken at times, even if there are those steps backwards that we also face as well. If we put you in charge of the new planning approach, give me your ideal city? What does a city look like to you? What is it? How is it built? Where do we live? How do we relate to each other? What’s your perfect city?

Well, it’s looking very different to what we’re doing now. You would have shopping centres underground or at least built into the ground much more. You would have residential areas that don’t have an architecture type that builds flat and wide. But it actually builds dense and high, 60, 70 storeys, I don’t have a problem with that. But you don’t use up the area that you freed by going from flat and wide to up and dense, all the surrounding area will be green infrastructure, parklands, lakes, recreational space, you cool your urban core. It will be built in a way that you have wind actually incorporated into the design. So, you can have hot days where you still get a breeze and it takes the heat out of the built environment.

It will look like what we call ‘sponge city’ and water that falls from the sky will be absorbed everywhere and become plant available for transpirative cooling. You also keep that water, which we’re now at the moment with this sprawl, of course we’re capping a lot of soil and that water, the stormwater needs to go somewhere. There’s a huge problem in the Sydney Basin, all the water that falls onto the basin is basically channelled as fast as possible out of the basin into the ocean. That means as we’re building more and more of the hard infrastructure and capping off our soils, we have more and more water to deal with.

I would change that to hold the water back because what happens is we have these flash floods going through our waterways where the water has a higher temperature because it’s been warmed by all this infrastructure. And of course, there are all the toxins that are washed off, lead, hydrocarbons and so on that go into the waterways. So, I would try to retain that water with designs that actually allow water infiltration and then store the water on site.

You could even see under big carparks because we would still have them, I would introduce underground water systems that store 3/400,000 litres, they are available, we can buy them, even made in Australia. So, they would sit under big car parks and store the water to irrigate in times, to keep everything nice and lush and cool, irrigate during times when we don’t have water. Because normally in Australia, I learnt you either have too much or too little, it never is right. So, to counter that situation, collect the water that you get when you have enough and when you don’t have enough, you have your storage, you use that for cooling. And of course, you would have much, much better public transport. I would definitely change that because I think it’s ridiculous for a place that houses six and a half million people and projected to house eight or nine million people, that you have the public transport at the moment that you see that we have in Sydney, I don’t think it’s good enough.

What’s the effect for people living in that city that you’ve designed? You’re telling them they’re living in high rises but is there more connection with others? Is there less? What’s the flow on effect?

First of all, you of course have the jobs where you live. You can walk to your office. This is what we’re trying at the Sydney Science Park to actually realise, to show that this is possible. You have your school right there, your childcare centre, your doctor’s practice, your cinema and your restaurant, it’s all there. So, the need to go 20 kilometres that way is gone. Of course, you need to design it beautiful, so aesthetically pleasing. Biophilic design is coming to the fore more and more.

When you look at high rise buildings, there are great ideas out there, instead of you come into the high rise building, go to the elevator and go up 60 floors, you can only go up ten floors and the 10th floor is like the social floor where you have open areas, green spaces, you have shops, you have your newspaper agent that was formerly the corner shop, which we see disappearing everywhere. You integrate that into these high-rise buildings where you have to change the elevator so you will meet people. So, you just again, you build smarter, I think there’s a lot of potential.

Also, what we see now with changing building materials, so not just our surfaces, but looking at cross-laminated timber, for example, as a construction material. We can do this. We even have a factory now for CLT, cross-laminated timber, in Australia. So, we have all of that, we just need to move and get those dinosaurs that just want to continue with business as usual, get them on board or increase the pressure that much from demand side that they simply can’t do anything else anymore.

You are so right that sometimes these changes are being held back by a few dinosaurs who have a lot of power and who essentially just don’t want to change. It’s a fear of change. How do we get the community to be excited by this change and come along on the journey?

Building something where you can go and physically experience the change that convinces people that you can do better. If you don’t show them how to do it and they can’t experience it physically, it’s very difficult because it becomes theoretical and then ‘Yeah, but I have something else to do and you know,’ that’s it gone. Moving on to the next topic. But if you get someone and you do a field trip with them, like with the car park, we already planning to have groups, even international visitor groups going to this car park to experience what can be done to change, because car parks, not just in Australia are a problem, it’s globally. You find them everywhere. What do you do? Well, you show people. When we have a conference, there’s an urban climate conference coming up, an international one in Sydney for next year, we will take people to the playground, we will show them what can be done and then they can take these ideas back home, they can start working on their own communities. It’s this effect that you get from exposing someone to the reality that has changed.

Well, this is amazing. If we can lead to car park tourism, people traveling just to see our wonderful carparks, I will know you’ve truly nailed your design there. Do you think we can make Western Sydney cool enough to be sustainable when global temperatures are rising? Can we do it?

We can. And this is where we need to be accurate again. We will not be able to change heat wave conditions. That’s too much energy stored in these synoptic events. Many, many, many hundreds, maybe even thousands of cubic kilometres of hot air moving from central Australia to the east coast. You can put trees there and paint the roads and put all the roofs into a white colour, that will not change that we will have heatwaves. Global change talks about 1.5 degrees and we already see with one point about four in Australia at the moment, the massive impacts that this has a very, very small change, but it’s that shift that pushes us into these more extreme climates.

We can if we put everything together, I’m convinced, we can reach about two to three degrees that we cool Western Sydney. That has locally huge benefits for people, it will lead to less energy, electricity consumption. It will have more heat safety built in because we don’t see the hot nights so frequent anymore. So, we’re not needing to cool anything down ten degrees, if we promise that we’re completely unrealistic. Trees themselves, are able to somewhere between 0.8 and 1.5 degrees lower that air temperature, maximum air temperature during the day about that much, if you’re really good and you’re providing them with all the water that they need and so on and so forth.

So, we should not overpromise and then under-deliver because we’ve done it too many times. But when we change the built environment, there’s some very nice studies also from colleagues from the UNSW uni, also from other unis here in Sydney that show once you start scaling, you do have an impact. And I would be very happy if we can say we reduced Western Sydney’s heat by two degrees in summer, when we look at summer maximum air temperatures, that we don’t have increased them as much as we increased them in other places where we didn’t plant all the trees because there are millions of trees going into the ground, which is good.

Exactly. We need to do with those obviously underlying causes of climate change, but we are going to have to deal with the consequences as well. We’re going to have to do these kind of experiments to make our cities more livable or I think it was as you described it, to go from livable cities to loveable cities. So, let’s hope that you have more success on that front. Please thank Sebastian for joining me, it’s been a lovely chat.

Thank you, Craig.

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