Extreme heat waves aren't just dangerous when they happen, say climate scientists.
They can also cause permanent damage. And the air conditioning is the main culprit.
The hotter it gets, the more people are using AC. And because of the way most power grids are set up, it means an increase in fossil fuel emissions.
A heat wave in the American West earlier this month shows how the vicious circle works.
Utah utilities in Arizona, Nevada, and Utah saw electricity demand surge to its highest level in at least 12 months when residents turned up the air conditioning.
This in turn led to an increased consumption of fossil fuels. Gas production reached annual highs in Nevada and Utah, while coal production in Arizona rose by more than a quarter compared to early June.
Analysts say the impact of individual heat waves on emissions is relatively minor. However, they warn that extreme temperatures represent a major long-term challenge for network planners and climate hawks alike.
Climate-induced weather changes are projected to increase electricity needs by 3% to 5% by the end of the century, said Michael Craig, a professor at the University of Michigan who studies the effects of climate change on electricity systems.
That in itself is not an insurmountable challenge, he said.
More worrying is how network operators plan extreme heat events, he said. In an effort to keep electricity flowing, network operators may slow down or abandon their plans to shut down the less efficient, dirtier fossil fuel power plants that often only run during heat waves. Keeping these facilities open increases the risks to the climate, said Craig.
“Then emissions will not only rise this year,” he said. “Those assets are hanging around and could be used and we have this long-term increase in emissions.”
Temperature and electricity demand have long been linked. In most of the United States, demand peaks in summer, is high in winter, and declines in spring and fall. The recent heat wave in the west is no different.
As temperatures rise, gas and coal production increases as utilities try to meet increased demand for electricity. This graph shows coal and gas production in the Arizona Public Service Co. and Salt River Project power systems, as well as temperatures at Phoenix Sky Harbor International Airport. Average daytime temperatures never dropped below 100 degrees Fahrenheit between June 14th and June 21st. Electricity generation from coal and gas increased 38% compared to the previous eight-day period. Claudine Hellmuth / E & E News (graphic); Energy Information Administration (electricity data), NOAA Climate Data Online (temperature data)
In Salt Lake City, the 107-degree Fahrenheit high recorded on June 15 was the highest temperature ever recorded in the city. Electricity demand rose to 175 gigawatt hours that day, the highest level in the past 12 months, according to a review of figures from the US energy agency E&E News. (The hourly network monitor numbers of the EIA only go back one year.)
Much of Utah's electricity is supplied by PacifiCorp, and much of the utility's electricity comes from coal-fired power plants in Wyoming. The 83 GWh coal production on June 15 was relatively modest by the company's standards. PacifiCorp has seen 93 days of higher coal production in the eastern portion of its six-state network, which includes Utah, over the past 12 months.
More notable in the case of PacifiCorp is the increase in gas generation during the recent heat wave. Three of the top five days for gas generation last year happened this month when high temperatures flirted with 100 degrees. The 43 GWh of gas generated on June 17 was the highest daily level in 12 months.
It was similar in neighboring Nevada, where Las Vegas peaked at 116 degrees on June 16. The Nevada Power Co. system's electricity demand peaked at 163 GWh on June 18, when the average temperature at McCarran International Airport reached a scorching 103 degrees. In comparison to Utah, Nevada is much more reliant on gas than on coal. Gas production in Silver State hit a 12-month high of 94 GWh on June 18. In comparison, coal production was 7.9 GWh.
Many energy experts are of the opinion that the dynamics are exemplary of how the power grid will eventually become greener. Gas-fired power plants – now the largest source of electricity in America – will run less as cleaner alternatives go online and eventually only be used during peak demand events, said Emily Grubert, a professor who studies power systems at Georgia Tech.
The bigger problem than the generation from individual systems is what rising temperatures do to the demand for electricity. A native of Southern California, Grubet noted that her parents installed air conditioning for the first time last year.
“It's basically all feedback loops and feedback loops,” she said. “Emissions are increasing because demand is increasing.”
So it was this month in Arizona. Demand for Arizona public service systems and the Salt River Project reached a 12-month high on June 17 and 18, during the four-day period when maximum temperatures were above 115 degrees.
While in Nevada and Utah gas was the main concern, in Arizona a shot of coal production went hand in hand with the increase in gas production. Coal production was nearly 38 GWh in the eight days between June 5 and 12, when daily temperatures averaged 93 degrees. Coal production rose to 47 GWh in the following eight days, with an average daily temperature of 103.5 degrees. Gas production increased by 58% during this time.
The increase in coal and gas production points to the traditional planning of electricity systems. Because they are reliable, utility companies turn to fossil fuels as demand increases. But fossil power plants struggle with extreme heat. Efficiency rates drop and equipment fails when the plants run at full capacity. Sometimes the water used to cool the plant gets too hot.
In a 2020 study of the Texas power system, Craig predicted that rising temperatures would cause up to 2 GWh of outages in fossil fuel power plants.
Maybe he was too conservative.
When temperatures soared in Texas earlier this month, roughly 9,000 GW of coal, gas, and nuclear capacity were offline, marginalizing the state's primary power grid (Energywire, June 15).
However, many of the cleaner alternatives also face challenges. Transmission lines – which are crucial for importing electricity in regions with increasing demand – lose efficiency at high temperatures. Solar generation can be hindered by smoke from forest fires; EIA reported that California's solar power decreased 30% in September 2020 compared to July due to forest fires burning across the state.
These challenges underscore the need to develop an electricity system for a warming world, said Craig.
“We are still thinking backwards and in the present, even though we should be partly thinking about the future because the future is coming quickly,” he said.