Prioritize...
After completing this section, you should be able to:
- Explain why green spaces, like parks within cities, can reduce the urban heat island effect.
- Define what a "cool roof" is and how it works.
Read...
We've just established that specific neighborhoods in cities get the "raw end of the deal." It’s obvious how this effect can be tied to climate change, too. As carbon emissions increase global temperatures, the number of extremely hot days become more common and intense. As this happens, it further stresses the warmest areas of cities, the areas already registering as the hottest in our current climate.
Let’s use another specific example. Over the past 25 years or so, New York City has averaged 3 days above 95°F during the summer months. However, there are estimates that, by 2075, the number could increase to 31 days -- a factor of 10! Below is a map of New York City from the same source we discussed previously, with the “South Bronx,” an area with a historical legacy of redlining, circled. As we saw before, this area is less affluent and has one of the most intense heat island effects within New York City as a whole. The infrastructure in neighborhoods like the South Bronx, often neglected and underfunded, is ill-equipped to deal with extreme heat. Many residents live in public housing where antiquated wiring limits the use of air conditioners. This creates dangerous living conditions during heatwaves. These conditions exacerbate health issues and stress, particularly for vulnerable populations like the elderly, young children, and those with pre-existing health conditions.
Below is another look at the same city and the same data using a different map and colorbar. The South Bronx pops out with lots of bright, nearly white dots -- along with many other neighborhoods in New York City, too.
So, what can we do about all this mess caused by redlining and climate change? While it is by no means a solved problem, there are some solutions on the table. First, we could start by planting more trees in these neighborhoods. Trees provide shade, cool down the area, and clean the air – greening inner cities can have a huge “bang for your buck!”
In one study, researchers used satellite data and climate models to identify the best strategies for cooling New York City. They first looked at the figure below and noticed that areas with high amounts of vegetation (grass, trees, etc.) tended to be cooler than surrounding areas of asphalt and concrete. To see this, compare the vegetation map below with the heat island effect map above that we just looked at. Notice how all the darker areas with more grass, trees, and other plants correspond to cooler temperatures? For example, Central Park in Manhattan sticks out like a sore thumb! I've annotated a few others as well. Feel free to load up Google Maps and scan for the green spaces yourself!
The scientists involved in this research ran simulations and showed that increased urban forestry and growing plants on roofs could lower New York City's average temperature by almost 2 degrees Fahrenheit throughout the day, with some areas seeing even greater reductions. And which areas saw the greater reductions? The ones that are the hottest and with the least green space at this time; the ones that are most likely to be stressed by climate change.
Satellite map of how “green” different areas of New York City are. Greener colors mean more trees and other plants, whereas whiter areas lack vegetation throughout whereas whiter areas lack consistent vegetation throughout and consist mostly of buildings and impervious surfaces like roads and parking lots.
Cool Roofs
Another promising solution is painting the roofs of buildings white. Remember when we learned about albedo earlier in the semester? Brighter (i.e., whiter) colors have a higher albedo and are, therefore, more effective at reflecting sunlight than absorbing it. As a result, white roofs are called "cool roofs." It sounds simple, but it really helps by reflecting the sun's heat instead of absorbing it, keeping houses cooler during those scorching summer days. Proponents of this argue that it provides a low-cost solution that helps buildings reduce energy costs and cool the atmosphere, particularly in highly urbanized areas. While there are some disadvantages, such as unwanted glare (not unlike walking outside on a sunny day after a fresh snowfall) and potentially higher heating costs in winter, the benefits during summer months are likely worth it in many areas. In addition to reducing urban heat island effects and decreasing risk in inner cities, roofs can improve air quality, reduce strain on the electrical grid, enhance comfort, and decrease emissions from power plants.
Painting roofs white or using lighter colored building materials can increase the albedo of urban areas during sunny days, reducing the amount of solar radiation absorbed and, therefore, reducing surface air temperature.
If the figure doesn't do it for you, here's a neat (and short!) video on "cool roofs" from the U.S. Department of Energy.
Video: Energy 101: Cool Roofs (2:16)
Narrator: Maybe you’ve never given much thought about what color your roof is or what it’s made of, but your roof could be costing you more money than you know to cool your home or office building, especially if you live in a warmer climate. Think about it this way: In the summertime, we wear light-colored clothes because they keep us cooler. Lighter clothes reflect rather than absorb the heat of the sun. It’s the same with your roof. A cool roof is often light in color, and made of materials that have what’s called high solar reflectance. That means it’s able to reflect a lot of the sun’s light that a conventional roof would absorb, heating up the building.
Narrator: You see, when the weather is warm, a conventional roof is the hottest place in the building. It can be well over 50 degrees hotter than the temperature outside. So if you don’t have air conditioning, a lot of that discomfort you feel may be coming from the roof. If a building with a standard darker roof is air-conditioned, the cost for comfort is much higher in order to counteract all that heat pouring in from above. Insulation slows the transfer of heat inside but doesn’t eliminate it. Researchers have measured energy savings up to 10 to 15 percent for homes with cool roof coatings. And if a standard dark roof reaches 150 degrees or more, a cool roof can actually reduce the roof temperature a lot. A cool roof may only be five or 10 degrees warmer than the temperature outside on a hot, sunny day. All right. So here’s a big plus for the environment. A cool roof helps mitigate a phenomenon known as the “urban heat island.” The temperature in developed urban areas tends to be two to five degrees warmer than surrounding areas. That’s because ground covered by pavement and dark buildings absorbs more heat. So the heat stays in the atmosphere longer. A variation of the cool roof is the green roof, sometimes called a living roof. That’s because flowers and plants and even a vegetable garden grow in a special soil system right on top of the building. Cool roofs aren’t super high-tech, and that’s part of their appeal. They’re a relatively simple and effective way to improve our environment and lower energy costs.
Lastly, it is crucial to enhance community support systems, particularly for the elderly and those more vulnerable during extreme heat or other adverse conditions. This can be achieved by organizing neighborhood watch programs, establishing cooling centers, and creating networks of volunteers to check on and assist at-risk individuals. Strengthening these community connections ensures that everyone receives the necessary care and support during challenging times. These steps won't fix everything overnight, but they’re a solid start toward making things fairer and cooler, literally!