Painting sidewalks white – literally applying layers of white paint onto dark concrete – is one of the various modern solutions that local governments have implemented in order to curb the effects of climate change and increasing global warming in cities. In May 2017, Los Angeles became the first city in California to actively battle increasingly-evident climate change by undergoing a twenty-year plan to paint the city’s sidewalks white. LA, in particular, experienced the harmful and imminent effects of climate change in 2017. The La Tuna wildfire in Verdugo Mountains, only twelve miles away from Downtown LA, was the largest wildfire LA county saw in decades and burned more than 7,000 acres of forestry, while other regions of California reached all-time high temperatures. This includes a high of 106 degrees Fahrenheit in San Francisco, where monthly average temperatures rarely rise above 70 degrees. Temperature increases around the world bear the mark of climate change and large ‘urban heat islands’ are responsible for a portion of this, as well as methods of combating it.
The Heat Island Group (HIG) is a collection of climate change and urban planning researchers at the University of California, Berkeley. Throughout their research at the Lawrence Berkeley National Laboratory, the HIG labeled a process the urban heat island (UHI) effect, or when outdoor daytime temperatures are directly impacted by the replacement of vegetation for heat-absorbing infrastructures, such as roads. Cities were referred to as urban heat islands respectively because large urban zones represented islands of color compared to live vegetation on thermal emissions maps. For example, the satellite image to the right depicts a city, where roads are represented by solid red lines and blue areas scattered around the photo and the upper right-hand corner shows clusters of vegetation.
The UHI effect is caused by a combination of urban surface properties and human activity. An average of 60% of U.S. city surface area consists of dark pavements, roofs, and even cars, which are typically dark-colored and impermeable. Consequently, city landscapes absorb at least 80% of incoming incident light. This phenomenon is explained in basic light principles, which overall state that dark surfaces absorb more wavelengths of light rather than reflect them, whereas light-colored surfaces reflect a majority of the incoming incident light. Thus, when light energy naturally converts to heat, dark surfaces experience a more rapid increase in temperature than light surfaces do. Similarly, they contain the heat longer. If you’ve ever been advised against wearing black clothing in the sun, this is why. You might literally be able to cook an egg on concrete because of how much energy it radiates. Additionally, radiated energy from various forms of human activity results in increased energy that propagates throughout a city to make it an urban heat island. The most common forms of energy emissions from human activity include transportation/gas products and industrial smog, both of which typically take place in concentrated amounts such as on freeways or in factory-designated areas of a city. Cities naturally fall prone to the UHI effect in order to accommodate for its population size and product demand, which also contribute to heat radiation with common household appliances, such as air conditioners and refrigerators. A majority of these everyday human activities also emit harmful pollutants into the atmosphere that further serve to contain heat within cities.
This climate phenomenon correlates to a positive feedback loop, which is defined as a process that amplifies changes in energy, or, in physics, defines increasing entropy of a system. Positive feedback loops mean increasing warmth in the atmosphere and are just one of the multiple atmospheric processes which contribute to global warming and climate change. Urban heat islands replicate a positive feedback loop of their own with such a prominent amount of dark surface area. With these factors combined, they can be 2-5 degrees Fahrenheit warmer than nearby rural areas. This not only serves as proof of how humans both contribute to and are impacted by climate change, but also of its potentially dangerous results. For LA, dark infrastructure and human activity emphasized through climate change resulted in a series of wildfires. Cities may even grow warmer than predicted because of natural disasters that decreased live vegetation. Local accountability is crucial.
The use of CoolSeal, paint predicted to keep pavement approximately ten degrees cooler than black asphalt, is how LA plans to tackle climate change. Lighter-colored streets will absorb and radiate less energy and result in a decreased temperature of city landscapes by a fraction, a reduction in the need for powerful air conditioning, and gradually improved air quality and city health conditions. Some skeptics were concerned about how bright cityscapes would appear as a result of white pavement, but an LA resident named Martha Ghosh confirmed in an interview with Los Angeles Daily News that the pavement is “not too bright” and expressed hopes for the project’s success.
Other cities around the world have tackled climate change by experimenting with reflective rooftops, planting thousands of trees to make up for local deforestation, and creating policies that encourage complete dependence on renewable energy resources. The cost of climate control methods is large, but the benefits can be too. There is an increasing need to tackle climate change — what are you doing to save the planet?