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Data from a heat wave reveal troubling trends. These four charts show the damage inflicted

Heat waves stress the electric grid system, forcing regulators to fire up dirtier power generators.David Paul Morris/Bloomberg

When smothering heat and humidity overtake the cool of spring, a familiar quest for relief begins, usually a trek to the basement or attic to dig out the window unit that’s been dormant all winter, or flipping on the central air. It brings welcome, sometimes lifesaving cool.

It is also a growing contributor to the already perilous climate problem. And in New England’s heat wave early this month — five days of 90 degree-plus heat, the longest June heat wave in nearly a century — peak electricity demand from air conditioning put 36 million extra pounds of carbon dioxide into the atmosphere.


That’s 3,551 cars driving for a year.

Or 18 million pounds of coal burned.

The eye-popping numbers are not necessarily unexpected, but they highlight an alarming phenomenon at work as climate change makes periods of extreme heat more common and prolonged: The warming climate is leading us into a dangerous vicious cycle.

“Climate change is driving more and hotter heat waves, which is forcing us to use our A/C units more, which is driving up emissions and causing more climate change and so on and so forth, perpetuating itself,” said Joseph Daniel, senior energy analyst with the Climate & Energy program at the Union of Concerned Scientists.

As long as the electrical grid powering those air conditioners draws from predominantly fossil fuels, it’s a trend that will continue. The state is working to power the grid with more renewable energy, but even under a best-case scenario, it is expected to take decades to completely transform it.

Meanwhile, the increased need for air conditioning during periods of intense heat will continue setting off a chain of other effects, compounding the impact of heat itself on public health, air quality, and a host of other effects. And those problems are likely to grow, around the world and in New England. By the end of the century, experts say, Massachusetts could see between 13 and 56 days of extreme heat each year, up from an average of four between 1971 and 2000.


For a snapshot of the issues that extreme heat present locally, the Globe compiled data that offer a vivid look at how the heat wave of June 5-June 9 affected our city, state, and region.

Air conditioning famously chews through massive amounts of electricity; According to data from grid overseer ISO-New England, by June 8, the fourth day of the heat wave, when temps reached 95 degrees, peak electricity demand soared some 66 percent over average daily use in the previous two months, most all of it likely attributable to air conditioning.

That’s not to say we can simply give up air conditioning.

“Saving lives today, in an increasingly heat-stressed world, is of paramount importance,” said Martin Hoerling, a research meteorologist in the National Oceanic and Atmospheric Association’s Physical Sciences Laboratory in Boulder, Colo. “I would feel that folks shouldn’t be making a ‘Sophie’s Choice’ between surviving heat waves while also wanting to secure a more habitable future world.”

From 2009 to 2015, the number of households in New England reporting they used air conditioning jumped nearly 7 percent, from 3.9 million to 4.2 million households, according to the most recent data from the Energy Information Administration.

Those sales spike especially during heat waves.

“This year, we have invested in a sizable inventory of air conditioners and have seen demand peak much earlier than in past years” as heat waves arrive earlier than usual, said Paul Conforti, the chief marketing officer for Ocean State Job Lot.


All of that excess energy demand means more carbon emissions, and more climate warming. On the hottest days, energy suppliers fire up what are called “peaker plants,” said Daniel, of the Union of Concerned Scientists. “These are by definition the most expensive power plants on the grid and they’re really only ever needed when energy demand peaks,” he said. “They tend to be older and dirtier.”

A 2020 report by the policy institute PSE Energy Health found that Massachusetts’ high-demand days are covered by 23 oil- and gas-fired peaker plants and peaking units at larger plants, including the oil-fired Canal plant in Sandwich and two oil-fired plants in Everett.

The report found that one-third of the state’s peaker plants have more than 100,000 people living within a three mile radius, and six of the facilities are in designated environmental justice areas, meaning communities where at least 25 percent of the population reports as non-white, non-English speaking and/or with a median income less than 65 percent of the statewide median.

These are also the areas most likely to feel the worst health impacts of a heat wave.

As air conditioners blast cool air inside a home, they can also contribute to an increase in emissions of particulate matter from the extra power plants needed to drive them, which reacts in the atmosphere and forms smog, and an increase in sulfur dioxide and nitrogen oxides, which can cause respiratory problems.


Across Massachusetts, as the temperature rose, air quality declined. Air monitors all over the state marked a change from good to moderate air quality as the heat wave settled in, according to EPA data.

And across the city, calls to Boston Emergency Medical Services rose. On Monday, June 7, EMS saw a 44 percent increase in call volume over what it typically sees.

Experts say there are a host of negative health impacts that can be triggered by heat waves, including respiratory problems, heat exhaustion, heart attacks, strokes, kidney problems, and more.

As with all heat waves, this one ended. As the temperature dropped, so did energy demand. The air across Massachusetts cleared. But the city and the state are preparing for more days like this, partially via plans to develop more clean energy and tackle climate change.

Late last year, the state released its 2030 Clean Energy and Climate Plan, which includes the goal of moving from the current 400,000 homes heating and cooling with electricity to at least 1 million homes by 2030. Successfully hitting that mark — while increasingly replacing fossil fuel power sources in the grid with renewables — will be a big step in achieving the state’s larger goal of net-zero greenhouse gas emissions by 2050.

Heat pumps run off electricity, using the refrigeration cycle to heat and cool by transferring thermal energy from a cooler space to a warmer space. They are far more efficient than window air conditioner units and central A/C, but the only way that heat pumps offer real climate savings is if they are powered by electricity created from clean sources of energy.


The state is also working on developing Clean Peak Energy Standard guidelines, which will gradually see peaker plants taken off line.

As the state develops more clean energy resources, gains in solar energy could also help meet the demands of increased heat waves. “The good news is that air conditioner demand — which is the primary driver for increased electricity demand — and solar output are strongly correlated,” said Daniel, of the Union of Concerned Scientists. “It’s not perfect, but we could certainly avoid the over-reliance of many of the dirtiest and least efficient power plants by building more solar and by pairing that solar with storage.”

Sabrina Shankman can be reached at sabrina.shankman@globe.com. Follow her @shankman.