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July’s heat wave led to stunning amounts of climate-warming pollution

A lineman from National Grid repairs a main line damaged from a fallen white pine on Hubbard Street in Lenox, Mass., on Tuesday, March 2, 2021. High winds knocked out power for thousands in the Berkshires.Ben Garver/Associated Press

A heat wave in New England last month — the first of the year — sent the mercury into the triple digits in some areas, sparked power outages across the region, and set off a spike in emergency calls.

It also led to a stunning amount of planet-heating greenhouse gas pollution due to increased energy usage, according to the regional grid operator, ISO-New England.

From July 12 to 25, power plants across the region emitted 845,967 metric tons of carbon dioxide pollution — a whopping 50 percent more emissions than New Englanders generated over same period last year.


Amid the climate crisis, heat waves are becoming more common in New England, which was traditionally known for its mild summers.

Spiking temperatures tend to increase electricity consumption, primarily because more people blast their air conditioners. That’s why electricity usage in New England is highest in the summer — especially on really hot days.

Hourly demand during last month’s heat wave peaked between 6 and 7 p.m. on Wednesday, July 20 at 24,330 megawatts.

That’s still lower than the peak demand ISO-New England forecasted for typical summer weather (known as the 50-50 forecast) and considerably lower than the 26,416 megawatt demand the operator predicted the region would see during especially hot and humid days (known as the 90-10 forecast).

Matthew Kakley, lead communications specialist for ISO-New England, said that peak demand stayed relatively low because July’s heat wave didn’t bring especially humid air — which makes temperatures feel even hotter than they are — to the region.

“What we observed during the July heat wave was that temperatures were very high, but dew points, while high, were not extreme,” he said.

Still, the emissions increase is concerning, especially in light of top climate scientists’ warnings that leaders must take steps to curb greenhouse gas pollution immediately to avoid catastrophic climate change. By 2030, state officials have pledged to achieve a 50 percent reduction in emissions. By 2050, they’ve promised to cut emissions by at least 85 percent and offset the remainder.


If the world fails to curb fossil fuel usage and slow climate change, experts project that periods of extreme heat are likely to increase significantly. From 1971 to 2000, the average summer in Massachusetts saw four days over 90 degrees. By mid-century, climate scientists say the state may have 10-28 days over 90 degrees each year. By the end of the century, Massachusetts could experience between 13 and 56 days of extreme heat each summer, depending on what steps are taken now to decrease greenhouse gas emissions.

Dharna Noor can be reached at Follow her on Twitter @dharnanoor.