San Antonio is getting hotter. And, yes, it is getting hotter because of climate change.  

Since 1859 we’ve known that adding carbon dioxide to the atmosphere will likely make the planet warmer. At this point, so many greenhouse gases have been pumped into the atmosphere that, if all humans totally stopped putting carbon dioxide and other greenhouse gas emissions into the air, the Earth would continue to get hotter for decades. This means for most of the people in San Antonio it will probably continue to get hotter for the rest of their lives.

Extreme heat is deadly to humans and to local economies. A report last year by the  Adrienne Arsht-Rockefeller Foundation Resilience Center projected that nearly 60,000 Americans could die annually from extreme heat by 2050. The same report projected U.S. labor-productivity losses at a half a trillion dollars annually by 2050. 

For the next generation, it is important to reduce greenhouse gas emissions. For this generation, however, there is a need to focus on mitigating increasing temperatures. Ways we can do this include planting trees in parking lots, using alternative transportation and implementing air conditioning technology that puts heat into the ground rather than the air. 

For 200 years we’ve been aware of a phenomenon that has become known as the “urban heat island,” in which cities are warmer than the surrounding countryside. A big part of this is due to the absorption of the heat from the sun by buildings, parking lots and roadways, which is then radiated back to the city environment. Paving and otherwise covering the ground with impervious surfaces prevents the natural cooling of the ground through the evaporation and transpiration of water. The trees, bushes, grass and water found in the countryside form the coolest ground cover there is.

Many studies have shown that the hottest parts of cities are often the poorest. They are found to be relatively hot usually because they lack the grass and trees found in other parts of the city.

A map depicts remotely sensed tree canopies across the City of San Antonio.
A map depicts remotely sensed tree canopies across the City of San Antonio. Credit: Courtesy / City of San Antonio

A study in Phoenix found that pavements contribute about 25 times the heat that vehicles do. Planting trees in parking lots, applying a cool pavement seal coat, and even depaving would help. San Antonio’s Office of Sustainability has identified those neighborhoods that are most vulnerable and continues to address this issue. The city’s popular One Roof program rehabilitates homes with cooler, energy-efficient white roofs.

Another category of heat source that researchers have inventoried in a city is from human activity, known as anthropogenic. Conventional air conditioning, for example, pumps the heat that is inside a building to the outside where it contributes to higher ambient temperatures. Driving motor vehicles, particularly those with internal combustion engines, adds to the heat through hot gases coming out of the tailpipe, rolling tire resistance, and heat radiating from the engine and other parts. One estimate is that 93% of the chemical energy in automobile fuel becomes sensible heat in the environment.

A heat map depicts land surface temperature in the night of August 18, 2014.
A heat map depicts land surface temperature in the night of August 18, 2014. Credit: Courtesy / City of San Antonio

Air conditioning is vital to the continued survival of San Antonio, but there are alternative technologies that could be used to avoid pumping hot air into the environment. One of the best puts heat in the relatively cool ground instead of the already hot air.  The largest application of this in the U.S. may be the Whisper Valley housing development in Austin.  The Institute for Local Self-Reliance has suggested using the vast municipal water pipe network as the connection with the ground as opposed to installing expensive new underground pipe. This could be a new revenue opportunity for the San Antonio Water System utility.

Our gradual transition to electric vehicles will certainly help with reducing urban heat. An electric vehicle produces about one-fifth of the heat of a conventional vehicle.  In the meantime, traveling by any other means than a single-occupant, fossil fuel-powered vehicle would reduce heat. Efforts to create housing and transportation alternatives will help citizens do this.

The task at hand certainly isn’t easy, but doing nothing will only make our city hotter. Let’s get to work making San Antonio a cooler city.

Bill Barker is recognized as a fellow by both the Institute of Transportation Engineers and the American Institute of Certified Planners.