ICU

The urban heat island results from heat accumulation by mineral surfaces (concrete, asphalt, roofs), lack of evapotranspiration (little vegetation), and anthropogenic heat released by air conditioners, vehicles and activities. The city-countryside difference is typically 2 to 4 °C on average, up to 8 to 10 °C at night-time peaks during heatwaves. Heat released by air conditioners significantly worsens the phenomenon: Salamanca et al. 2014 (Journal of Geophysical Research: Atmospheres) measured +1 °C at night in Phoenix due to air conditioner operation alone. Negative feedback loop: the hotter it is, the more air conditioning is used, the more heat is released outside, the warmer the city becomes. No individual carbon inventory measures this collective cost.