More extreme heat and bigger populations will dramatically change energy use in American cities by 2050, driving up the amount of electricity used to cool urban buildings per unit of floor area by at least 20% in some areas, according to research published Oct. 18 in Nature Communications.
Commercial and residential buildings are among the nation’s major energy consumers, and they account for just under a third of U.S. greenhouse gas emissions when researchers consider the emissions associated with burning fossil fuels to provide buildings with electricity.
As a result, planning for future climate conditions will require understanding of how building energy use is likely to change with more extreme weather and populous cities, said lead study author Chenghao Wang, who worked on the research as a postdoctoral scholar in the lab of Stanford University professor Rob Jackson.
Worldwide, space cooling is one of the biggest drivers of growing demand for electricity in buildings and the addition of new generation capacity to keep the electric grid functioning when demand for power peaks. “We’re locked in a vicious cycle where warming is turning air conditioning into a necessity rather than a luxury,” said Jackson, who is the Michelle and Kevin Douglas Provostial Professor at the Stanford Doerr School of Sustainability and the study’s senior author.
“We’re locked in a vicious cycle where warming is turning air conditioning into a necessity rather than a luxury. ”
Zooming in on cities
To assess climate change impacts on building energy use in urban areas from coast to coast, the researchers combined physics-based simulations and statistical analysis of building energy use, historical weather data, and projections of future climate conditions for 277 cities under four global warming scenarios. They also considered two possible trajectories for decarbonization of the electric power sector: one with rapid decarbonization driving emissions to net zero by 2050, and the other with no further emission reduction policies beyond 2021.
“Previous studies made strides in estimating how energy use might change at the national or state levels in response to future changes in climate,” said Wang, who is now an assistant professor in the University of Oklahoma’s School of Meteorology and Department of Geography and Environmental Sustainability. “However, there is a significant gap in our understanding when it comes to the city scale. As global cities commit to ambitious sustainability goals, a more granular understanding of energy use at the city scale becomes imperative.”
“Simply put, to achieve carbon neutrality by 2050, we need rapid electrification for future urban buildings.”
More peak energy hours
The team focused their analysis on an indicator called energy use intensity, or EUI, which is calculated by taking the total energy consumed by all buildings in a given region, and dividing it by their floor area.
The researchers discovered that the increase in electricity EUI during warm seasons and the hottest days will be much greater than the annual change, especially in the Northwest, mainly due to greater use of air conditioning. For each degree (Celsius) of warming at the city scale, the energy used per square foot to cool urban buildings will increase on average by nearly 14%. For space heating, the authors estimate it will drop by 9-11% with each degree of warming, with the exact percentage depending on whether buildings use electricity, gas, oil, or propane for heating.
Electricity use by buildings in U.S. cities will peak more often during the hot summer months in the coming decades, the researchers found, with cities including Seattle and San Francisco seeing twice as many “peak energy hours” in the 2050s compared to the 2010s under many future climate scenarios. “This will require higher grid capacity and also greater resilience against power outages during extreme heat waves,” Wang said.
The team also assessed the source energy used by urban buildings, which includes the amount of energy lost during generation, transmission, and distribution and affects overall greenhouse gas emissions. “Power sector decarbonization is very effective in improving electricity generation efficiency and curbing the source energy consumption,” Wang said. “But it’s crucial to further reduce direct fossil fuel combustion in buildings,” by switching water heaters, stoves, and space heaters from running on fossil fuels to electricity, he said. “Simply put, to achieve carbon neutrality by 2050, we need rapid electrification for future urban buildings.”
This story was adapted from a press release originally published by the University of Oklahoma.