Cities are extremely hot — trees cool them down

July was Earth's hottest month ever .

The United Nations says we're entering an "era of global boiling ."

The greenhouse gases we've released into the atmosphere by burning fossil fuels since the Industrial Revolution are warming the planet and making extremes in weather more frequent and more intense.

It’s even hotter in cities , which can be 1–7oF hotter during the day and 2–5oF hotter at night, compared to surrounding non-urban areas.

Meanwhile, more and more of the global population is moving to cities. By the UN’s estimate, 2 out of every 3 people globally will live in cities by 2050, a change mostly driven by developing countries.

(This is generally a good thing—people generally tend to have better quality of life in cities because of things like better access to healthcare, education, employment, and clean water. Cities generate wealth.)

Cities globally account for about 75% of global CO2 emissions, with buildings and transport as the biggest contributors, respectively. (In my native New York City, buildings generate 71% of CO2 emissions and use 94% of electricity .)

So cities have an imperative to decarbonize, not just because it's the right thing to do, but because it makes sense for the bottom line. We are going to solve the climate crisis with innovations and investments that both remove carbon and eliminate our reliance on fossil fuels, but that's a topic for another day...

Today, I want to talk about adapting our cities to our temporarily warming world.

Reducing urban heat at scale

We don't want our cities to be insanely hotter, which is bad for everything from public health to grid stability to worker productivity. Instead, we need to focus on solutions that reduce urban heat at scale. Here are some of my favorites:

Trees, water, and green spaces

Trees, water, and green spaces all help mitigate extreme temperatures. They're also beneficial for reducing rainwater runoff, lenthening the life of pavement, creating habitat, sequestering CO2, and improving air quality. They also provide natural protection from noise pollution and the general congestion of city life. I loved this post from Ecosia , which clearly showcased the cooling benefits of urban trees:

Plus, water and greenery add beauty and character to urban areas, which not only makes life more pleasant but also increase property values and tenant demand.

Green roofs can also be beneficial, where possible and appropriate.

Painting streets and roofs with reflecting coating

Some cities like Los Angeles, Phoenix, and Tokyo are trying their hand at painting streets and roofs with a reflective coating, to higher the albedo effect and bounce more heat away than black asphalt.

According to a report by the US Environmental Protection Agency (EPA) , if 35% of Los Angeles' streets were covered with a reflective surface, the average air temperature could be reduced by 1oF on a hot day...which is not as significant as what trees can do, but it's an interesting solution nonetheless.

Cool buildings more efficiently

Buildings use the majority of energy in any city, and much of this energy goes towards heating and cooling. On an especially hot day, demand for electricity spikes. Existing buildings can cool themselves more efficiently by:

• Selecting optimal cooling equipment
• Regularly servicing cooling equipment
• Ensuring good insulation
• Generating renewable energy on-site via rooftop solar or geothermal
• Using smart controls and sensors
• Installing smart windows that automatically dim when it's bright
• Replacing air conditioners with heat pumps

What can be done?

My recommendation is pretty simple: plant more trees and invest in building energy efficiency.

Increased public green spaces bring innumerable benefits to cities, not only by reducing urban heat islands but also improving human health and quality of life.

More energy efficient buildings, on the other hand, are an imperative to decarbonize the real estate industry. Buildings are responsible for the majority of CO2 emissions in any city, and this carbon impact can be greatly reduced (and owners can save money and avoid carbon fines) by cooling buildings more efficiently.

Cool roofs and reflective surfaces are great mitigation ideas and work as a quick fix, but I believe the future of cities need to look to nature.

For those interested in further reading, some cities already doing this well include Seoul, Minneapolis, Medellín, Paris, Toronto, and Guangzhou.