Greenhouse gas emissions will spike today as temperatures along the East Coast approach triple digits and grid operators fire up nearly all of their power plants to help Americans beat the heat.

The spike in emissions as temperatures rise is a characteristic of the nation’s electric grids. Many of the dirtiest coal- and oil-fired power plants sit idle for most of the year, because it doesn’t pay to run them. That changes on hot days. Residents and businesses turn on their air conditioners, pushing electric demand up and prompting grid operators to call on their seldom-used plants.

“As the number of extreme heat days goes up, we’re going to need more peak power, and that will create more carbon dioxide unless we have a clean electric system that can handle it,” said Constantine Samaras, a professor who studies power-sector emissions at Carnegie Mellon University.

The situation highlights a potentially dangerous loop. As the planet warms, heat waves like the one gripping much of the United States will become more common. And as the mercury rises, so do people’s reliance on fossil fuels, creating even more pollution.

Extreme weather alone doesn’t push greenhouse gases higher. U.S. emissions have trended downward in recent years, even as global temperatures climbed, largely because power plants have generated less pollution during the course of a year. But 2018 underlined the potential dangers of extreme weather. Electricity demand surged on the back of a particularly cold winter and hot summer, pushing overall emissions up for the first time in several years (Climatewire, Jan. 10).

Samaras framed the situation like this: “The number of extreme heat days is one factor that will determine how much power we will use in a year.”

Temperatures are expected to approach 100 degrees Fahrenheit in Chicago; New York; St. Louis; and Washington, D.C., today, according to the National Weather Service. The extreme heat will linger over the Eastern Seaboard into the weekend.

Grid operators were projecting an increase in electricity demand as a result. The PJM Interconnection, which covers Mid-Atlantic states from Virginia to Illinois, said it expected demand to surge to 152 gigawatts. PJM’s peak demand last summer was 150 GW. Its all-time peak was recorded in August 2006, when demand hit 165 GW.

It was a similar story in New York and New England. ISO New England was expecting demand to reach 25 GW, short of its record peak in 2006 of 28 GW. The New York Independent System Operator said demand was expected to crest above 30 GW. New York’s record peak was 33 GW in 2013.

“Electricity from oil and coal power plants is generally more expensive than other types of generation, so they are typically not dispatched (unless needed for reliability) until demand rises,” Marcia Blomberg, a spokeswoman for ISO New England, wrote in an email. “When demand is high, more oil and coal plants are likely to be needed, and that could cause an increase in emissions.”

July and August were responsible for 22 out of the 25 highest emission months nationally between 2001 and 2018, according to Carnegie Mellon University’s power-sector carbon index.

The high emissions months coincided with increased coal use.

That’s changing, as more coal plants are replaced with natural gas and renewable energy sources. In August 2008, when electricity generation and carbon emissions hit a 17-year peak, coal accounted for 45% of power production. Electricity generation was nearly as high in July 2018, but emissions were 24% lower. Coal’s share of electricity generation at that time: 28%.

Heat waves offer a lifeline to aging coal and oil plants, said Joe Daniel, who tracks the power sector at the Union of Concerned Scientists.

“Days like today and this week drive up power prices to the point where it makes economic sense to keep them running,” Daniel said. “These hot summer days are being used to keep otherwise uneconomic coal plants alive.”

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.