Business Insider Edition

New York City has painted over 557,000 m² of rooftops white — and it could be a brilliant heat-fighting plan

Peter Kotecki , Business Insider US
 Aug 14, 2018, 03:44 PM
(Getty Images)

  • New York City has painted over 557,000 m² of rooftop white in the past nine years.
  • Reflective paint can decrease the temperatures inside buildings and lower air conditioning costs. 
  • Los Angeles is also taking steps to use more reflective paint, spending about $40,000 (R560,000) per  mile (1.6 kilometre) to paint streets white.
  • Scientists believe that light roofs could help alleviate some of the worst effects of climate change.
  • However, some experts say this may not be the best way to lower temperatures because of potentially negative consequences on the environment.

Summers in New York can be extremely hot, and the city is taking steps to reduce the temperatures inside buildings through a program that most New Yorkers don't even see.

Since 2009, New York City has used at least 557,000m² of paint in free roof upgrades to non-profits, hospitals, and affordable housing buildings. The CoolRoofs programme hired 70 people last year to help coat roofs with white paint, which can significantly decrease buildings' internal temperatures and lower air conditioning costs, according to Small Business Services, which runs the programme.

In general, cities are hotter than rural areas because their asphalt roads and concrete buildings absorb heat. Local temperatures in cities can be higher, which can increase air pollution, cause heat-related deaths, and drive up air conditioning costs.

Light-coloured roofs could help cool cities and alleviate some of climate change's worst effects. It can even act as a l0w-stakes version of geoengineering, or intervening with the planet's climate system to reverse global warming — without the potentially dangerous consequences  of other approaches like solar geoengineering.

New York is not the only city to use white paint in an effort to reduce temperatures; Los Angeles is spending $40,000 (R560,000) per  mile (1.6 kilometreto paint the city's streets white. White paint gets sprayed on roads by a truck, and city workers with squeegees then distribute the coat evenly.

Black or dark-coloured asphalt can absorb up to 95% of the sun's rays, but by covering it with white paint, the streets would be up to 5.5°c cooler.

Some experts worry that painting roofs white may not be the best way to cool a city, according to The New York Times. It is not clear, for example, if reflective roofs are more effective than planting trees. 

Arizona State University professor Matei Georgescu, the lead author of the 2014 study, wrote that reflective roofs could have negative consequences in places like Florida, where Georgescu and his team found that white paint led to less local rainfall. 

Rain can typically evaporate back into the air after falling onto the ground, allowing more rain to fall. This process is driven by heat, so a reduction of heat through the application of white roof paint would prevent as much water from evaporating and producing rain.

Scientists also do not believe that reflective surfaces can eliminate the need to reduce greenhouse gas emissions. However, every little steps is helpful in light of global temperatures rising. Since 2000, more than 128,000 people in the world have died from severe heat waves. 

Despite some scientists' criticism, New York's CoolRoofs programme is going strong. According to the Mayor's Office of Sustainability, every 230m² of painted roof is lowering the city's carbon footprint by one ton of emissions.

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