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Extreme Temperatures: How North American Cities Amplify Climate Change

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After record-breaking heat in the summer, 2023 is on track to be the hottest year ever.


Sustainability Leaders podcast is live on all major channels including AppleGoogle and Spotify.


A hotter world will reshape economies and industries

Cities, which house 4.4 billion people and comprise 80 percent of global GDP, are increasingly facing challenges associated with climate change, such as extreme heat.

Across North America, millions of people live in cities where extreme heat already occurs. And urban populations are growing. In the US and Canada, nearly 90 percent of residents will live in cities by 2050.

Cities are heat islands — they are hotter than surrounding areas because of heat-absorbing dark surfaces (buildings, roads, parking lots) and a proportional reduction in natural areas. As a result, the impacts of extreme heat are most concentrated where economic activity is highest and social costs are great.

Mind the extreme temperature gaps

A recent BMO Climate Institute and Climate Engine analysis examines this phenomenon in major U.S. and Canadian cities.

Canadian cities have some of the largest gaps between extreme temperatures in the urban core relative to the surrounding countryside.

A graphic comparing recent high land surface temperatures inside of and outside of six major cities in North America.

From supply chains to prices at the pump

Extreme temperatures will have a pronounced effect on sectors critical to the low-carbon transition, such as power generation, agriculture, construction, and energy use in buildings, with potential knock-on effects to consumers.

We have already seen a glimpse of the economic impact. Cumulative losses attributed to heat-induced events are estimated to be between US$5 trillion to US$29 trillion globally between 1992 and 2013.

Supply-chain disruptions, power outages, transit delays, and infrastructure failure all become more likely under conditions of extreme heat.

Productivity can also diminish with each degree increase in heat. Looking ahead to 2030, the International Labour Organization estimates that 2 percent of total working hours worldwide could be lost annually due to extreme heat, eroding economic output by US$2.4 trillion.

High temperatures can hit closer to home as well. For instance, the cost of U.S. home energy in the summer is estimated to have increased 12 percent because of extreme temperatures. Heat-related refinery outages were also a factor contributing to increased U.S. gasoline prices this summer.

Miami-Dade County is one of the first places in the world to appoint an official dedicated to improving equitable community resilience to extreme heat. Jane Gilbert, chief heat officer for Miami-Dade County, has focused on encouraging more investment in retrofitting homes with energy efficient cooling systems and expanding tree planting and tree preservation efforts. “Both the tree planting and energy-efficient retrofits really help all of us transition to the cleaner energy economy and to address our urban heat islands,” she said on an episode of our Sustainability Leaders podcast.

North American extreme heat projections

Extreme temperatures—those above 32℃—are projected to happen more often, under multiple warming scenarios.

A graphic showing a map of North America with colors indicating the probability in 2050 of days spent annually at extreme temperatures in a scenario based on the world’s current path on climate change.

Business implications

Now is the time to plan for climate risks associated with extreme heat, especially for companies operating in, or doing business in, areas where extreme heat is projected to become increasingly common. While companies operating in some of the hottest areas today must prepare for more frequent heat events, it is also important for business leaders to identify where their operations might not have endured extreme heat historically but could begin to have an impact in the coming decades.

The 2023 BMO Climate Institute Business Leaders Survey showed that 34 percent of U.S. and Canadian respondents say that severe weather, including heat waves, are already impacting their businesses. In addition, 31% of respondents say operational disruptions are top of mind when it comes to climate change.

As they develop climate plans, business leaders will need to consider the impact of extreme heat across their entire value chain, including the effect on customers and employees. As part of an ambition to be its clients' lead partner in the transition to a net-zero world, BMO is committed to helping customers understand climate risk, is integrating best available climate science and geospatial analytics to inform how we support our clients and communities in which we operate, and is providing tools such as Climate Smart to help companies understand their carbon footprint and reduce emissions.

For more insights about climate risk, explore the following BMO Climate Institute publications:

Read more

Jane Gilbert:

Cities are getting hotter not only because of climate change, but how we develop. More buildings and asphalts, more waste heat from vehicles and buildings, HVAC systems, less trees, less vegetation. All of this results in our urban environments being up to 10 degrees hotter than the surrounding natural areas.

Michael Torrance:

Welcome to Sustainability Leaders. I'm Michael Torrance, Chief Sustainability Officer with BMO Financial Group. On the show, we will talk with leading sustainability practitioners from the corporate, investor, academic, and NGO communities to explore how this rapidly evolving field of sustainability is impacting global investment, business practices and our world.

Speaker 3:

The views expressed here are those of the participants and not those of Bank of Montreal, it's affiliates or subsidiaries.

George Sutherland:

Hi there. My name is George Sutherland from the BMO Climate Institute. In today's episode of Sustainability Leaders, we'll be talking about trends in extreme heat and their intersection with our social and economic systems, as well as the actions that people, communities, and governments can take to help mitigate these impacts.

While temperatures may be starting to cool in the Northern Hemisphere autumn, a retrospective look at this past summer shows that it was the warmest on record and with these elevated temperatures come more frequent and severe heat waves. To help me unpack this, I'm joined by Jane Gilbert, Chief Heat Officer for Miami-Dade County. Jane was the first chief heat officer named globally and is one of the few people to hold this title. Thank you for joining me, Jane.

Jane Gilbert:

It's a pleasure.

George Sutherland:

Now the title of chief heat officer is likely new to many. So to begin our discussion, could you describe what the responsibilities are for a chief heat officer?

Jane Gilbert:

Yes, of course. When Mayor Daniella Levin Cava, the mayor of Miami-Dade County, appointed me in May of 2021, so about two and a half years ago. She charged me with addressing the increasing health and economic impacts of rising temperatures here in Miami-Dade County. So we've looked at vulnerability assessment of who's most impacted and then engaged wide range of stakeholders in the development of our action plan. And now we're in heavy implementation mode of that plan.

George Sutherland:

So that sounds like a broad mandate with a focus on building resilience to extreme heat. And to that point, what are the current trends that you've observed related to extreme heat?

Jane Gilbert:

So we're coming off an unprecedented hot summer, but historically our trend from, say 1985, has been an average minimum temperature increase of about 2.2 degrees Fahrenheit or degrees Centigrade. But this past summer we just had dramatic increase, 10 times the number of extreme caution days. And those we define here in Miami is days where the heat index at or above 105 degrees Fahrenheit, which is a little over 40 degrees Celsius.

And historically, just in the last 14 years with climate change baked in, we've had about six days out of the year where we've hit those heat indices of 105 or more, 40 degrees Celsius or more. This past summer we had over 60 days with a heat index over 105 or more, so over 10 times the number of extreme caution days.

George Sutherland:

And why are these trends particularly concerning for people who live in cities?

Jane Gilbert:

So cities are getting hotter not only because of climate change, but how we develop. More buildings and asphalt, more waste heat from vehicles and buildings, HVAC systems, less trees, less vegetation. All of this results in our urban environments being up to 10 degrees hotter than the surrounding natural areas. And it's very unequal. So we have certain areas with 40% tree canopy that are much cooler and those tend to be higher income areas.

And then we have areas with less than 10% tree canopy, and those tend to be our lower income, more vulnerable populations that are living there. They're having to pay more to keep their homes cool. It's oppressive to walk and wait at a bus stop and they can't afford to be in an AC car. So these are the areas that we need to double down our investments.

George Sutherland:

And listeners may be familiar with the term of the urban heat island effect, which you're referring to. This is the idea that's due to the concrete and the asphalt surfaces as well as heat output from vehicles and buildings, and also the corresponding loss in natural spaces. Cities tend to be hotter than the surrounding countryside.

Jane Gilbert:

Yes.

George Sutherland:

Now more than half of the world's population lives in cities. And as a result of that, most of the world's economic activity is also concentrated in cities. And we see that at the same time, cities are expected to grow larger with continued trends in urbanization while they are also simultaneously projected to get hotter as climate change is locally intensified in cities by the urban heat island effect.

So it strikes me that there are some important economic implications associated with this, and I wonder if you could speak to what some of those economic or financial impacts of extreme heat can be?

Jane Gilbert:

Yes. One of the largest economic impacts that we're feeling right now is lost labor productivity due to extreme temperatures. Organization, the Adrienne Arsht-Rockefeller Foundation Resilience Center, did a study of globally some of the impacts due to labor productivity loss alone, the economic impacts, and looked at 12 cities globally including the Miami metropolitan area.

And they found that we are currently experiencing about $10 billion economic impact due to high temperatures causing lost labor productivity, lost time on the job, and that is projected to double by mid-century to $20 billion a year.

George Sutherland:

So these are substantial economic impacts, and layered on top of that are also the social costs of extreme heat. Could you speak to this as well?

Jane Gilbert:

So I started to talk a little bit earlier about the difficulty people can have with staying cool at home affordably. That is a big piece. Our lower income populations, a large group of them are paying very high utility costs just to stay cool, or they're having to opt to not turn on the AC and then put themselves and their families in harm's way with the levels of heat. And so it's a difficult choice they're making. We also have over 300,000 outdoor workers in Miami-Dade County that are increasingly exposed to those high temperatures.

In other words, those 105 degree temperature days that are getting more intense as we get hotter. So that's another impact. People that get to work by public transit and walking, we've had people end up in the emergency room because they had to wait at a bus stop that was unshaded for too long. So all of these are... And then there's just quality of life changes, right? Kids in summer camp can't be outside as much, or parents can't take their kids to the playground. It's in all times of day and times a year. So those are some definite quality of life impacts as well.

George Sutherland:

And you've touched on this earlier, but just to unpack in further detail, you mentioned that urban spaces aren't created equally. So what does this mean for how extreme heat is experienced across cities and what inequities exist?

Jane Gilbert:

So when we did our vulnerability assessment for Miami-Dade County, I really wanted to understand what populations were having the highest rates of heat-related illnesses and where those were. And so we looked at heat-related emergency department visits and hospitalizations by zip code. And we have great disparity. We have some zip codes with four and five times the rate of heat-related emergency department visits and hospitalizations and other zip codes in Miami-Dade County.

And the top correlating factors are high poverty rates, high land surface temperatures, so our urban heat islands, and high percentage of outdoor workers. So people living in these low tree canopy, high asphalt, dense areas are really suffering more from this significantly. We also partnered with our university partners on placing sensors in different areas of the county.

And they too found that when the national weather surface is projecting a certain temperature based on, say the forecasting at the Miami International Airport. There are other neighborhoods that could be experiencing up to 10 degrees higher temperature than that and not be aware that it's actually extremely dangerous where they are.

George Sutherland:

And this drives home what we already know, which is that the transition to a low carbon future must be inclusive. So what is required to make urban spaces more resilient to heat extremes while ensuring that this is achieved in an equitable and an inclusive manner?

Jane Gilbert:

So there are two big interventions that we're investing in that both address helping low income people adapt to extreme heat, but also address our low carbon future. So one is to increase our investments in home weatherization programs and energy efficient retrofits and making sure that we're providing not only passive but active, highly efficient cooling retrofits for people's homes so that they can bring their utility costs down. We can bring our greenhouse gas emissions down at the same time.

The other area is doubling down on tree planting and tree preservation efforts in our areas with less than 20% tree canopy in greater than 20% poverty rates. 90% of our investments last year, we increased our funding last year by 2.5 million. We're increasing it again this year to 3 million. So we've been increasing each year and we just got a $10 million Inflation Reduction Act grant for the next five years.

So we're doubling down on our tree canopy enhancement, particularly in these urban heat island areas. So both those tree planting and those energy efficient retrofits really help all of us transition to that cleaner energy economy and to address our urban heat islands.

George Sutherland:

And what type of initiatives has Miami-Dade County implemented to advance this?

Jane Gilbert:

So our plan has three main goal areas. One is to inform and prepare people. So we declared May 1st through October 31st as an official heat season, and our goal is to raise public awareness on the level that Miami-Dade County has raised public awareness and preparedness around hurricanes. And so we've done bus shelter, bus stop ads, particularly in the zip codes with the highest rates of heat-related illnesses, radio spots, television, social media.

But also trained community disaster volunteers, trained summer camp providers, trained our cooling site staff and partnered with the healthcare community on enhancing the healthcare practitioners understanding of how to look at how chronic high heat exposure can exacerbate other existing conditions and make sure they're asking the right questions and coding those illnesses correctly. So a lot of training and outreach. That's the first goal area. Also in that is to work towards protecting our outdoor workers.

So we held three trainings for employers to put in health safety plans. In the United States, the Occupational Safety and Health Administration is in the process of creating a heat safety standard, but right now they don't have one. So there's only guidelines. So we're working towards potentially having an official heat standard for Miami-Dade County. That's another policy we're working on.

Certainly we've updated the policy for all our own county workers and are rolling out those trainings and making sure that all our workers under our care are protected from that heat. So that's all within that first goal area. The second one is to help people cool their homes. And so we talked a little bit about upping weather mitigation programs, multifamily retrofits, but also to make sure that our cooling sites have backup power and can operate in the event of a widespread power outage.

Then last is that tree canopy and that urban heat island mitigation. So in addition to all the tree planting that I mentioned earlier, we're going to be piloting cool pavements and looking at enhancing our access to drinking water and water features more broadly in the public realm.

George Sutherland:

You mentioned cool pavement as one of the solutions. Could you share a bit more on how this is being applied?

Jane Gilbert:

Sure. So a cool pavement is a pavement that has what's called a high albedo, a high reflectivity, just like cool roofs. We already have a requirement in Miami-Dade County that all low slope roofs have to meet a certain albedo level. This is similar, although it's not as standardized as the cool roofs. In other words, it hasn't been as well tested out there.

LA and Phoenix have rolled out pretty strong pavement pilots and programs, and we're looking to do some of the same to understand where does that work well, how well does it stay up over time, maintained over time, because a white pavement can get pretty dirty over time, and so we're looking and piloting it, but it has been shown to be able to reduce urban heat island effect.

George Sutherland:

And are there examples of other cities that are leading through action?

Jane Gilbert:

Absolutely. There are a lot. In fact, I now have seven or eight other chief heat officers around the globe that I get to interact with on an ongoing basis. But even beyond that, there are cities like Boston or Tucson, Arizona or Austin, Texas that I've interacted with that have been doing great work on heat without a chief heat officer. And even in Canada, I've interacted with some folks up in Canada interested in learning more about what we're doing here and acting on initiating their own heat action plans.

George Sutherland:

And is action only limited to governments, or are there also things that homeowners or communities can do to help protect themselves against extreme heat?

Jane Gilbert:

Absolutely. We need all hands on deck to address these issues. So as individuals, we can protect, we can learn how to note, how to protect ourselves, our loved ones, our workers from the impacts of extreme heat, and make sure that we take those precautions.

As homeowners, we can retrofit our homes to make them highly efficient and bring down both the costs, but the emissions that are associated with those homes, and certainly in our neighborhoods, to advocate for more trees, less pavement, ideally native plantings that can preserve the habitat, help absorb storm water and filter the storm water in addition to cooling down the neighborhood.

George Sutherland:

What resources can people explore to learn more?

Jane Gilbert:

I think the Biden administration has put together a very effective website. It's called heat.gov, so I encourage people to take a look at that. And then the Arsht-Rock Resilience Center created an extreme heat action platform for local governments that are looking to create their own action plans. It's sort of a primer on how to do that.

George Sutherland:

And we'll include links for those resources in the show notes. Lastly, in a few weeks, world leaders will be gathered at COP28 in Dubai to negotiate progress on global climate goals. What are you watching for and hoping to see come out of this meeting?

Jane Gilbert:

So some of the most powerful agreements that have come out of previous COPs have been at the sub-national level led by cities. And cities are, as you mentioned at the beginning of this interview, the drivers of population growth and economics and greenhouse gas emissions. So we have the potential to really address issues at that level.

So I would hope that a coalition of subnational governments get together and commit to addressing urban heat islands through also means that will bring down greenhouse gas emissions from the built environment and from the transportation sector, as well as investing in nature-based solutions in tree canopy. And so that's what I would really like to see from COP28.

George Sutherland:

Well, Jane, thank you very much for joining me to discuss trends in extreme heat, how this intersects with our urban environment and what can be done to mitigate these impacts.

Jane Gilbert:

Well, it was my pleasure, George.

George Sutherland:

That's Jane Gilbert, Chief Heat Officer for Miami-Dade County. Stay tuned for more episodes of Sustainability Leaders where we will host leading experts and continue to explore the impacts of climate change on our social, financial, and natural systems.

Michael Torrance:

Thanks for listening to Sustainability Leaders. This podcast is presented by BMO Financial Group. To access all the resources we discussed in today's episode and to see our other podcasts, visit us at bmo.com/sustainabilityleaders. You can listen and subscribe free to our show on Apple Podcasts or your favorite podcast provider, and we'll greatly appreciate a rating and review and any feedback that you might have.

Our show and resources are produced with support from BMO's marketing team and Puddle Creative. Until next time, I'm Michael Torrance. Have a great week.

Speaker 6:

For BMO disclosures, please visit bmocm.com/podcast/disclaimer.

 

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