Burlington is warming up along with the rest of the world as the climate crisis changes weather patterns around the globe.
While Vermont may not be having extreme heat waves, fires, or flooding like some parts of the American West, the climate crisis is impacting the state in significant ways. Eastern Vermont has had poor air quality over the past few days because of the Manitoba fires in Canada, and Burlington beaches have had unusually frequent cyanobacteria blooms this summer.
Within Burlington city limits, the impact of climate change may become especially profound. A recent study by Climate Central revealed the city is more than 7 degrees warmer — a result of its design and layout — than rural areas of the state that are experiencing the same climate conditions. The score is known as the urban heat island intensity index and is an average of temperature readings taken throughout the city compared to temps in surrounding rural areas. That means some areas of the city are even warmer, while others are much cooler.
The difference in temperature by neighborhood loosely corresponds to average income levels in neighborhoods throughout the city: Higher-income neighborhoods have cooler temperatures, and lower-income neighborhoods are generally warmer.
The Climate Central study examined cities through several lenses when calculating how much heat they trap, taking into account greenery, permeable surfaces, population density, building height and albedo — a measure of how much a city absorbs or reflects solar radiation. Burlington did well in several areas, such as greenery. However, it struggled with albedo, meaning the city has unusually low solar reflection and instead absorbs heat.
Last month, Burlington posted record high temperatures for June, reaching the mid-90s on June 6. While the state historically has had only half a dozen days of 87-plus temperatures per year, that number is expected to increase to more than 20 days per year, according to state data.
In Burlington, the impact of that heat will be felt particularly strongly.
Heat waves can have profound public health impacts, such as increased hospitalizations for outdoor workers, young children and people with underlying respiratory issues. But even when heat waves are not extreme enough to affect public health, generally increasing temperatures have long-term effects on the local ecosystem. Burlington’s capacity for trapping heat only exacerbates that.
Professor Kris Stepenuck, who studies watershed science and policy at the University of Vermont, said urban heat islands can affect local waterways, plants and animals.
“We know that plants in urban heat islands require more water. Plants in the most urban areas can drink up to 10 percent more water than in a cooler rural place,” Stepenuck said.
Particularly in cities with low albedo scores like Burlington, it is common to see local water sources heat up. High temperatures of pavement, sidewalks and rooftops heats up stormwater runoff, which then flows into local lakes, ponds and streams. That can change the aquatic ecosystem, killing fish and other wildlife, and leading to new bacteria blooms.
In Burlington, stormwater runs off into Lake Champlain. Burlington City Councilor Jane Stromberg said warming stormwater may have profound impacts on the lake’s ecosystem. According to the Vermont Department of Health, cyanobacteria — whose blooms have shut down Burlington’s swimming beaches repeatedly this summer — grow more quickly in warm water.
Stromberg said Burlington’s high urban heat intensity index is a major concern for the city, and needs to be addressed rapidly.
“This heat island problem will cause lots of long-term natural resource issues that will be very prominent if we don't do anything,” Stromberg said.
How did we get here?
Researchers say there’s been a trend of low albedo scores in cities throughout the Northeast, which are absorbing more solar radiation than cities in other parts of the country, such as the Southwest.
Angel Hsu, professor of public policy and energy at the University of North Carolina at Chapel Hill, said several factors could play into this trend.
“There are cultural preferences like different climatic regions,” she said. “Places where it’s really hot often don’t have brick because it’s just really hot and brick heats up, but in the Northeast you might have more brick homes because it’s a cooler climate. Some of it is just a matter of the background climate in these areas.”
Britta Fenniman Tonn, a modern architectural historian and preservationist in Burlington, said the city’s unique architectural style arose through a combination of climate considerations, the availability of natural resources, and shifting architectural trends of the 19th and 20th centuries.
“First and foremost, Burlington’s architecture is dictated by what the popular architectural style was during an era, so beginning in the 1830s, when development really picked up in Burlington, that was the Greek revival style, featuring lots of stone,” she said. The Pomerleau Building near the waterfront is an example of that architectural style.
Tonn said some of the earliest homes in Burlington were designed to trap heat. “Houses had large hearths and chimneys located very centrally in the building with compartmentalized interiors, so the warmth could be concentrated in one specific room, which was obviously important in Burlington with the cold winters,” Tonn said.
In the 1860s, Burlington — along with the rest of the Northeast — transitioned to Victorian and Queen Anne architectural styles, which Tonn said dominate modern Burlington. “The Wells House on University of Vermont’s campus is a really good example of a Victorian building executed in brick,” Tonn said.
During the rise of Victorian architecture, Burlington benefited from having easy access to wood and slate building materials. The city was a major lumber port and Vermont had slate deposits along its western border. As a result, wooden homes with slate roofs are very common.
“We see a lot of slate in Vermont because it's a native building material. Slate tends to be a little darker, so when you’re thinking of trapping heat that could be a factor,” Tonn said.
In the 19th century, Burlington also enacted ordinances requiring that brick be used for commercial buildings, because it is fireproof. Tonn said the prevalence of brick buildings in Burlington also arose from Italian architectural trends that made their way to New England.
“The city was following architectural trends of the 19th century, so the italian-age style was really popular during that time when a lot of the buildings on Church street were built,” Tonn said. “The idea behind it is mimicking an italian villa.”
Peter Clavelle, who was mayor of Burlington from 1998 until 2006, said Burlington’s beloved architecture contributes to its urban heat problem.
“Burlington architecturally is an attractive city,” Clavelle said, “and one of the things that makes it attractive are these buildings that were constructed out of brick. But brick buildings contribute to urban heat islands more than, say, white colonial buildings.”
The U.S. Green Building Council provides LEED (Leadership in Energy and Environmental Design) certifications for buildings that meet specific green building standards, said Stephen Selin, co-founder of Selin and Selin Architecture in Shelburne. LEED certification isn't a requirement in Vermont or in Burlington, but the certification is a bit like a farm being organic-certified — it can be a selling point for businesses. The certification takes into account how much heat the building will trap.
“What they use to see if a building is contributing to a heat island effect is the solar reflectance index — how much sun a building or a driveway reflects back into the atmosphere, Selin said. “High numbers are best. Like white has a really high number and black has a really low number.”
Materials such as slate, which are naturally dark in color, by default have a low solar reflectance score, while lighter materials such as clay have a higher score.
Selin said the shape of a roof can also affect solar reflectance. “Flat roofs reflect everything right back up,” he said. To get LEED certification for a building with a flat roof, the roof must be painted white or have vegetation. However, buildings with sloped roofs have less impact on solar absorption or reflection because they don't face directly up into the atmosphere, so roof color requirements are more flexible for buildings with sloped roofs.
Even if LEED certification isn’t being pursued, Selin said, keeping LEED standards in mind even when building private homes can help create cooler cities. Selin said he strives to design buildings that align with those standards, but if a client doesn’t have the budget for it or doesn't make it a priority, there isn’t much he can do.
However, the Vermont Residential Building Energy Standards and the Vermont Commercial Building Energy Standards enacted in 1998 and 2006, respectively, do set some energy requirements for buildings that can mitigate heat trapping. However, historic buildings constructed before those standards were enacted are not subject to the same requirements.
Urban heat islands have been studied for only a few decades, and as recently as 10 years ago, city planners and architects may not have been designing cities with urban heat islands in mind.
In fact, some city planning efforts that lower greenhouse gas emissions can actually contribute to urban heat island intensity.
Clavelle said during his time as mayor in the late 1990s and early 2000s, urban heat island mitigation was not yet a major priority for the city. In fact, some of his efforts to make Burlington more energy-efficient may have contributed to the city’s trapped-heat problem,
“We pursued and created strategies that resulted in more concrete and asphalt in the city,” Clavelle said. “We were faced with the choice between concentrating growth and development or allowing sprawl to occur. We decided sprawl was not what we wanted because that’s not how you create healthy, vibrant cities, and it requires people to drive more.
“But lots of asphalt and concrete in dense downtowns also heat up a city.”
What can be done?
While Burlington may be nearly 7 degrees warmer than it needs to be right now, the good news is that city officials and residents can cool down the city with the right mitigation efforts.
Stromberg said inefficient use of space in the city is one thing she would like to change. “Even just looking down on our city in Google Earth, you can see a lot of parking lots, and many of them aren’t being used to full capacity. I think that’s a huge contributor.”
Stromberg hopes to limit the number of parking spaces businesses can provide, aiming to decrease the amount of heat-absorbing asphalt throughout the city.
Clavelle said converting unoccupied parking areas and other large stretches of asphalt and concrete into “pocket parks” would be a great way for the city to cool down and provide more green spaces for residents.
Stepnuck, the researcher at UVM, is active in the Raise the Blade campaign, which urges Vermont homeowners to let their grass grow about an inch longer than average. Longer grass reduces stormwater runoff, which can ease some of the ecological impacts of low albedo.
“When we infiltrate more rain into the ground, then we aren't sending heated stormwater into the lake where it can cause ecosystem damage,” Stepnuck said.
Samantha Sheehan, Mayor Miro Weinberger’s spokesperson, said via email that “the climate action work being led and executed by the city is very far-reaching.”
“The work underway across the city to fight climate change and mitigate its harmful impacts is led by many departments across the city team,” she wrote. “For example, in the Department of Public Works, countless efforts are underway to adopt more sustainable practices — using permeable pavers, designing stormwater gardens, planting hundreds of trees, modernizing our water resources, infrastructure, and more.”
Other solutions include keeping climate in mind when building new developments. Building to LEED standards, planting vegetation on roofs, and employing natural cooling via airways through buildings can have a significant impact not only on decreasing heat absorption in the city, but also on cooling down residents to avoid some of the most serious public health impacts of the heat island effect.
Stromberg acknowledged that a lot of Burlington’s buildings are historic and were built when energy efficiency and heat mitigation weren’t being considered yet. She says there are ways to preserve old buildings while also updating them, so they are better adapted to the changing climate — like weatherizing and retrofitting old buildings to make them more efficient. And, improving insulation, sealing off windows and creating reflective roofing can help cool down cities.
“We’re at that stage of climate adaptation; we have to make these changes because we know that climate change is here,” Stromberg said.