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Existing global energy projections underestimate the impact of climate change on urban heating and cooling systems by roughly 50% by 2099 if greenhouse gas emissions remain high, researchers report. This disparity could profoundly affect critical sustainable energy planning for the future.

Existing studies predominantly concentrate on chemical feedback loops, which are large-scale processes involving complex interactions between energy use, greenhouse gas emissions and the atmosphere. However, a research group led by the University of Illinois Urbana-Champaign focuses on the often-overlooked physical interactions between urban infrastructure and the atmosphere that can contribute to local microclimates and, ultimately, global climate.

A new study led by civil and environmental engineering professor Lei Zhao emphasizes that smaller-scale city-level waste heat from residential and commercial property heating and cooling efforts can lead to big impacts on local climates and energy use. The study findings are published in the journal Nature Climate Change.

"The heat generated from heating and cooling systems is a substantial part of the total heat generated within urban areas," Zhao said. "These systems generate a lot of heat that is released into the atmosphere within cities, making them hotter and further increasing the demand for indoor cooling systems, which feeds even more heat into local climates."

This process is part of what researchers call a positive physical feedback loop between building cooling-system use and the warming of local urban environments. The authors also note that rising temperatures under climate change could potentially decrease energy demand during the colder months, a negative feedback loop that should be considered in any temperature and energy demand projections.

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