Pavement in Phoenix is now hot enough to cause serious burns, causing a rise in burn cases from falls. ”pavement temperatures can easily reach 160 to 170 degrees F” said Kevin Foster, director of the Valleywise Health’s Diane & Bruce Halle Arizona Burn Center in Phoenix. “New Heat Map Shows Scorching Streets that Can Burn Skin in Seconds”, https://www.scientificamerican.com/article/new-nasa-heat-map-shows-scorching-streets-that-Acan-burn-skin-in-seconds/. While severe burns are clearly a problem, do these high surface temperatures have other implications?
A few days after the article on skin-burns, the Associated Press warned, “More records expected to shatter as long-running blanket of heat threatens 130 million in U.S. (https://apnews.com/article/heat-wave-record-temperatures-2ca3046bf74ca596b24a2879d8dcf664) Phoenix set a new record of 1180 F, and Death Valley beat its record by 50 F.
A few days after that, the AP noted record breaking heat in Las Vegas, setting an all-time record of 1200 F. https://apnews.com/video/heat-waves-las-vegas-weather-national-national-ff1279056240469998be30ca8a240201
Climatic warming has been attributed to heat trapped by greenhouse gases. But where does the heat come from?
When I first went to Australia with my wife, I noticed how much things cost. Australians understood this. They know they are a small economy, a long way away, and shipping is expensive. That is all true. Because they understood the reasons for high prices, they did not seek additional evidence. They saw high-prices as unfortunate, but an acceptable cost for living in a wonderful country. I saw their acceptance as a license for high prices. Shop owners could charge whatever they wanted, and would not be challenged on price.
It is the same for greenhouse gases. Once science discovered that greenhouse gases trap heat, raising temperatures, no further cause for increasing temperatures was sought. But does the climate science discovered before greenhouse gases provide Insight?
Luke Howard (1772 – 1864), an English chemist (pharmacist) was the first to document and analyze heat islands. He published “The Climate of London: Deduced from Meteorological Observations” in 1818, with a second volume in 1820.
The importance of the planet’s surface was discovered in the 1820s when Fourier, (1768 – 1830) a French physicist and mathematician, recognized that: “The atmosphere…. absorbs infrared radiation rising from the earth’s sun-warmed surface” (Henson, 2019:30).
Howard determined that London was 1.570F warmer than surrounding areas. In urban areas today, home to over half the world’s population, heat islands are typically 50F to 90F above outlying areas. However, a doctoral dissertation notes a case where temperatures were 260F higher, (Kim, JP, & Guldmann, JM, 2014). Differences of that magnitude reflect the conditions we see in these heat waves.
Howard’s analysis of the causes of higher urban temperatures is effectively the same as current experts. Lisa Garland (2011) lists the six causes of heat islands as:
- Reduced evaporation.
- Increased heat storage.
- Increased net radiation.
- Reduced convection.
- Increased Anthropogenic heat.
- Systemic interactions.
Garland lists “Reduced evaporation” as the primary cause of increased temperatures. Evaporation requires moisture. Howard noted: “the country has an almost inexhaustible store of moisture to supply its evaporation – that of the city is very speedily exhausted, even after heavy rain.” (Howard, 1820: 106).
Therefore, dry environments, and anywhere drainage systems prevent rainfall from soaking into the soil, as is the case in most urban and many suburban areas, experience reduced evaporation and increased temperatures. Because most evaporation takes place as transpiration through vegetation, reducing vegetation and increasing bare soil also decreases transpiration. That condition is made worse when the soil is covered with pavement. Is It any wonder cities in arid climates like Phoenix and Las Vegas are setting new highs?
The other causes result more directly from the built environment. Increased heat storage is a function of the properties of construction materials. Increased net (heat capturing) radiation is largely a function of the proximity of buildings, and their geometric relationships. Decreased convection is a function of buildings blocking the cooling effects of air-flow. Anthropogenic heat is the thermal pollution we create, intensified in urban areas where populations are denser. Systemic interactions are the ways each of these, impact the others.
However, the context is problematic. While measuring heat islands against surrounding areas is the generally accepted practice, it obscures reality. Certainly, suburban and rural outlying areas have more vegetation and less of the heat generating and trapping conditions of cities. But development destroys nature, reduces photosynthesis and transpiration, and increases heat generation from sunlight. To a greater or lesser extent, the entire planet has been impacted by these conditions. Where will you find “undisturbed,” outlying areas?
That fact has two implications. One, we have underestimated the extent of heat islands because we have no “0” baseline to measure against. And two, the entire planet is radiating excess heat. We have created a Heat Planet.
Thus, the conversion of sunlight into heat is the source that creates heat islands, and increasingly warms the atmosphere. Greenhouse gases, trap that heat like a pot lid, exacerbating warming. But to reduce the elevated temperatures we are experiencing, we need to address the source of the heat generation, akin to turning down the stove.
Christopher Haines can be reached at [email protected]
References
Garland, L (2011) Heat Islands: Understanding and Mitigating Heat in Urban Areas. Washington D.C.: Earthscan Publishing.
Henson, R, (2019) The Thinking Person’s Guide to Climate Change, 2nd Ed. Boston, Ma. American Meteorological Society.
Howard, L, (1820) the Climate of London: Deduced from Meteorological Observations Volume 2. London, W. Phillips, George Yard. (2012, New York, Cambridge University Press.)
Kim, Jun-Pill & Guldmann, Jean-Michel (2014) Land-use planning and the urban heat island, Environment and Planning B: Planning and Design, v 41:1077 – 1099.
