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New rules governing how companies report their scope 2 emissions have pit tech giant against tech giant and scholars against each other.

All summer, as the repeal of wind and solar tax credits and the surging power demands of data centers captured the spotlight, a more obscure but equally significant clean energy fight was unfolding in the background. Sustainability executives, academics, and carbon accounting experts have been sparring for months over how businesses should measure their electricity emissions.
The outcome could be just as consequential for shaping renewable energy markets and cleaning up the power grid as the aforementioned subsidies — perhaps even more so because those subsidies are going away. It will influence where and how — and potentially even whether — companies continue to voluntarily invest in clean energy. It has pitted tech heavyweights like Google and Microsoft against peers Meta and Amazon, all of which are racing each other to power their artificial intelligence operations without abandoning their sustainability commitments. And it could affect the pace of emissions reductions for decades to come.
In essence, the fight is over how to appraise the climate benefits of companies’ clean power purchases. The arena is the Greenhouse Gas Protocol, a nonprofit that creates voluntary emissions reporting standards. Companies use these standards to calculate emissions from their direct operations, from the electricity and gas that powers and heats their buildings, and from their supply chains. If you’ve ever seen a brand claim it “runs on 100% renewable energy,” that statement is likely backed by a Greenhouse Gas Protocol-sanctioned methodology.
For years, however, critics have poked holes in the group’s accounting rules and assumptions, charging it with enabling greenwashing. In response, the organization has decided to overhaul its standards, including for how companies should measure their electricity footprint, known as “scope 2” emissions.
The Greenhouse Gas Protocol first convened a technical working group to revise its Scope 2 Standard last September. By late June, the group had finalized a draft proposal with more rigorous criteria for clean energy claims, despite intense pushback on the underlying direction from companies and clean energy groups.
A flurry of op-eds, essays, and LinkedIn posts accused the working group of being on the “wrong track,” and called the proposal a “disaster” with “unintended consequences.” The Clean Energy Buyers Association, a trade group, penned a letter saying it was “inefficient and infeasible for most buyers and may curtail ambitious global climate action.” Similarly, the American Council on Renewable Energy warned that the plan “could unintentionally chill investment and growth in the clean energy sector.”
Next the draft will face a 60-day public consultation period that begins in early October. “There’ll be pushback from every direction,” Matthew Brander, a professor of carbon accounting at the University of Edinburgh and a member of the Scope 2 Working Group, told me. Ultimately, it will be up to the Working Group, the Protocol’s Independent Standards Board, and its Steering Committee, to decide whether the proposal will be adopted or significantly revised.
The challenge of creating a defensible standard begins with the fundamental physics of electricity. On the power grid, electrons from coal- and natural gas-fired power plants intermingle with those from wind and solar farms. There’s no way for companies hooking up to the grid to choose which electrons get delivered to their doors or opt out of certain resources. So if they want to reduce their carbon footprints, they can either decrease their energy consumption — by making their operations more efficient, say, or installing on-site solar panels — or they can turn to financial instruments such as renewable energy certificates, or RECs.
In general, a REC certifies that one megawatt-hour of clean power was generated, at some point, somewhere. The current Scope 2 Standard treats all RECs as interchangeable, but in reality, some RECs are far more effective than others at reducing emissions. The question now is how to improve the standard to account for these differences.
“There is no absolute truth,” Wilson Ricks, an engineering postdoctoral researcher at Princeton University and working group member, told me back in June. “I mean, there are more or less absolute truths about things like how much emissions are going into the atmosphere. But the system for how companies report a certain number, and what they’re able to claim about that number, is ultimately up to us.”
The current standard, finalized in 2015, instructs companies to report two numbers for their scope 2 emissions, based on two different methodologies. The formula for the first is straightforward: multiply the amount of electricity your facilities consume in a given year by the average emissions produced by the local power grids where you operate. This “location-based” number is a decent approximation of the carbon emitted as a result of the company’s actual energy use.
If the company buys RECs or similar market-based instruments, it can also calculate its “market-based” emissions. Under the 2015 standard, if a company consumed 100 megawatt-hours in a year and bought 100 megawatt-hours’ worth of certificates from a solar farm, it could report that its scope 2 emissions, under the market-based method, were zero. This is what enables companies to claim they “run on 100% renewable energy.”
RECs are fundamentally different from carbon offsets, in that they do not certify that any specific amount of emissions has been prevented. They can cut carbon indirectly by creating an additional revenue stream for renewable energy projects. But when a company buys RECs from a solar project in California, where the grid is saturated with solar, it will do less to reduce emissions than if it bought RECs from a solar project in Wyoming, where the grid is still largely powered by coal, or from a battery storage project in California, which can produce clean power at night.
There are other ways RECs can vary — for instance, companies can buy them directly from power producers by means of a long-term contract, or as one-off purchases on the spot market. Spot market REC purchases are generally less effective at displacing fossil fuels because they’re more likely to come from pre-existing wind and solar farms — sometimes ones that have been operating for years and would continue with or without REC sales. Long-term contracts, by contrast, can help get new clean energy projects financed because the guaranteed revenue helps developers secure financing. (There are exceptions to these rules, but these are broadly the dynamics.)
All this is to say that the current standard allows for two companies that consumed the same amount of power and bought the same number of RECs to report that they have “zero emissions,” even if one helped reduce emissions by a lot and the other did little to nothing. Almost everyone agrees the situation can be improved. The question is how.
The proposal set for public comment next month introduces more granularity to the rules around RECs. Instead of tallying up annual aggregate energy use, companies would have to tally it up by hour and location. To lower companies' scope 2 footprints further, purchased RECs will have to be generated within the same grid region as the company’s operations, and match a distinct hour of consumption. (This “hourly matching” approach may sound familiar to anyone who followed the fight over the green hydrogen tax credit rules.)
Proponents see this as a way to make companies’ claims more credible — businesses would no longer be able to say they were using solar power at night, or wind power generated in Texas to supply a factory in Maine. While companies would still not be literally consuming the power from the RECs they buy, it would at least be theoretically possible that they could be. “It’s really, in my view, taking how we do electricity accounting back to some fundamentals of how the power system itself works,” Killian Daly, executive director of the nonprofit EnergyTag, which advocates for hourly matching, told me.
The granularity camp also argues that these rules create better incentives. Today, companies mostly buy solar RECs because they’re cheap and abundant. But solar alone can’t get us to zero emissions electricity, Ricks told me. Hourly matching will force companies to consider signing contracts with energy storage and geothermal projects, for example, or reducing their energy use during times when there’s less clean energy available. “It incentivizes the actions and investments in the technologies and business practices that will be needed to actually finish the job of decarbonizing grids,” he said.
While the standard is technically voluntary, companies that object to the revision will likely be stuck with it, as governments in California and Europe have started to integrate the Greenhouse Gas Protocol’s methodologies into their mandatory corporate disclosure rules.
The proposal’s critics, however, contend that time and location matching will be so costly and difficult to implement that it may lead companies to simply stop buying clean energy. One analysis by the electricity data science nonprofit WattTime found that the draft revision could increase emissions compared to the status quo if it causes a decline in corporate clean power procurement. “We’re looking at a potentially really catastrophic failure of the renewable energy market,” Gavin McCormick, the co-founder and executive director of WattTime, told me.
Another concern is that companies with operations in multiple regions could shift from signing long-term contracts for RECs, often called power purchase agreements, to relying on the spot market. These contracts must be large to be beneficial for developers because negotiating multiple offtake agreements for a single renewable energy project increases costs and risk. Such deals may still make sense for big energy users like data centers, but a company like Starbucks, with cafes throughout the country, will have to start sourcing fewer RECs in more places to cover all the parts of the world where they operate.
The granularity fans assert that their proposal will not be as challenging or expensive as critics claim — and regardless, they argue, real decarbonization is difficult. It should be hard for companies to make bold claims like saying they are 100% clean, Daly told me. “We need to get to a place where companies can be celebrated for being like, I’m not 100% matched, but I will be in five years,” he said.
The proposal does include carve-outs allowing smaller companies to continue to use annual matching and for legacy clean energy contracts, even if they don’t meet hourly or location requirements. But critics like McCormick argue that the whole point of revising the standard is to help catalyze greater emission reductions. Less participation in the market would hurt that goal — but more than that, these accounting rules aren’t designed to measure emissions, let alone maximize real-world emission reductions. You could still have one company that spends the time and money to invest in scarce resources at odd hours and achieves 60% clean power, while another achieves the same proportion by continuing to buy abundant solar RECs. Both would still get to claim the same sustainability laurels.
The biggest corporate defender of time and location matching is Google. On the other side are tech giants Meta and Amazon, among others, arguing for an approach more explicitly focused on emissions. They want the Greenhouse Gas Protocol to endorse a different accounting scheme that measures the fossil fuel emissions displaced by a given clean energy purchase and allows companies to subtract that amount from their total scope 2 footprint — much more akin to the way carbon offsets work.
If done right, this method would recognize the difference between a solar REC in California and one in Wyoming. It would give companies more flexibility, potentially deploying capital to less developed parts of the world that need help to decarbonize. It could also, eventually, encourage investment in less mature and therefore more expensive resources, like energy storage and geothermal — although perhaps not until there’s solar panels on every corner of the globe.
This idea, too, is risky. Calculating the real-world emissions impact of a REC, which the scope 2 working group calls “consequential accounting” is an exercise in counterfactuals. It requires making assumptions about what the world would have looked like if the REC hadn’t been purchased, both in the near term and long term. Would the clean energy have been generated anyway?
McCormick, who is a proponent of this emissions-focused approach, argues that it’s possible to measure the counterfactual in the electricity market with greater certainty than with something like forestry carbon offsets. With electricity, he told me, “there's five minute-level data for almost every power plant in the world, as opposed to forests. If you're lucky, you measure some forests, once a year. It's like a factor of 10,000 times more data, so all the models are more accurate.”
Some granularity proponents, including Ricks, agree that consequential accounting is valuable and could have a place in corporate reporting, but worry that it’s ripe for abuse. “At the end of the day, you can't ever verify whether the system you're using to assign a given company a given number is right, because you can't observe that counterfactual world,” he said. “We need to be very cautious about how it’s designed, and also how companies actually report what they’re doing and what level of confidence is communicated.”
Both proposals are flawed, and both have potential to allow at least some companies to claim progress on paper while having little real-world impact. In some ways, the disagreement is more philosophical than scientific. What should this standard be trying to achieve? Should it be steering corporate dollars into clean energy, accuracy of claims be damned? Or should it be protecting companies from accusations of greenwashing? What impacts do we care about more, faster emissions reductions or strategic decarbonization?
“They’re actually not opposing views,” McCormick told me. “There’s these people making this point and there’s these people making this point. They’re running into each other, but they’re actually not saying opposite things.”
To Michael Gillenwater, executive director of the Greenhouse Gas Management Institute, a carbon accounting research and training nonprofit, people are attempting to hide policy questions within the logic and principles of accounting. “We’re asking the emissions inventories to do too much — to do more than they can — and therefore we end up with a mess,” he told me. Corporate disclosures serve many different purposes — helping investors assess risk, informing a company’s internal target setting and performance tracking, creating transparency for consumers. “A corporate inventory might be one little piece of that puzzle,” he said.
Gillenwater is among those that think the working group’s time- and location-matching proposal would stifle corporate investment in clean energy when the goal should be to foster it. But his preferred solution is to forget trying to come up with a single metric and to encourage companies to make multiple disclosures. Companies could publish their location-based greenhouse gas inventory and then use market-based accounting to make a separate “mitigation intervention statement.” To sum it up, Gillenwater said, “keep the emissions inventory clean.”
The risk there is that the public — or indeed anyone not deeply versed in these nuances — will not understand the difference. That’s why Brander, the Edinburgh professor, argues that regardless of how it all shakes out, the Greenhouse Gas Protocol itself needs to provide more explicit guidance on what these numbers mean and how companies are allowed to talk about them.
“At the moment, the current proposals don’t include any text on how to interpret the numbers,” he said. “It’s almost incredible, really, for an accounting standard to say, here’s a number, but we’re not going to tell you how to interpret it. It’s really problematic.”
All this pushback may prompt changes. After the upcoming comment period closes in late November or early December, the working group could decide to revise the proposal and send it out for public consultation again. The entire revision process isn’t estimated to be completed until the end of 2027 at the earliest.
With wind and solar tax credits scheduled to sunset around then, voluntary action by companies will take on even greater importance in shaping the clean energy transition. While in theory, the Greenhouse Gas Protocol solely develops accounting rules and does not force companies to take any particular action, it’s undeniable that its decisions will set the stage for the next chapter of decarbonization. That chapter could either be about solving for round-the-clock clean power, or just trying to keep corporate clean energy investment flowing and growing, hopefully with higher integrity.
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Generate Capital, CalSTRS, and the Rhodium Group have teamed up on a new Transition Acceleration Framework to measure and assess emissions impacts.
The most common way to judge whether a company or project is helping to tackle climate change is to measure emissions. Has the company reduced its carbon footprint? Will the project add fewer greenhouse gas emissions to the atmosphere than alternatives?
It’s a useful metric, but a limited one. One company might be doing more to advance the energy transition than another — by investing in an expensive, early-stage solution such as geothermal power, for example — but a comparison of their carbon footprints won’t necessarily show it. At the project level, a solar farm in Mississippi, where solar deployment has lagged, will do more to decarbonize the U.S. power grid than one of equal size in California, even though both projects emit zero carbon.
This presents a challenge for climate-minded investors like Jonah Goldman, the chief strategy officer of Generate Capital, who are trying to figure out where their dollars can make the biggest difference. To solve it, Goldman worked with colleagues at the California State Teachers Retirement System, which backs Generate’s investments, and a team at the Rhodium Group to develop a new way for investors to assess where to put their money.
“The question that most of the frameworks out there ask is, what are your carbon emissions today, and can your carbon emissions be lowered?” Goldman told me. “The Transition Acceleration Framework asks, how can you apply capital that has the best chance of getting to decarbonization over a reasonable time frame?
“It sounds like a similar question. It sounds like semantics. But it’s actually quite different,” he said.
At a high level, the Transition Acceleration Framework measures how much additional decarbonization a given investment can deliver beyond what would likely have occurred anyway. It can also be used to evaluate policy interventions and procurement decisions, such as where to get power for a data center. The Rhodium Group published a white paper describing the methodology on Thursday, as well as an accompanying report using it to evaluate options for powering data centers in the U.S.
The Transition Acceleration Framework has three components: transition potential, transition efficiency, and acceleration factor.
Transition potential is “the size of the emissions-reduction opportunity,” the white paper says — it measures the gap between the current trajectory for a given technology and its potential deployment in a deeply decarbonized world. Some of the solutions with the highest transition potential scores, per Rhodium’s analysis, include light duty electric vehicles and utility-scale solar.
Transition efficiency measures how effective a dollar spent on that technology can be at closing the gap, based on an estimate of the total capital expenditure required to realize the potential. There, more nascent solutions like low-carbon cement and geothermal power score higher than EVs and solar.
Rhodium combines these two complementary metrics into a single “technology factor,” a score on a scale from one to ten that can help identify the highest-leverage sectors to invest in. (The project is similar in spirit to Heatmap’s Decarbonize Your Life series, in which we tried to determine the highest-leverage actions a given individual could take to cut emissions. If you missed it, check it out.)
While the transition potential and efficiency metrics provide a high-level view into how transformative different types of investments can be, the third component of the framework — the acceleration factor — helps distinguish between specific projects.
This starts with an assessment of five “acceleration attributes” — cost reduction, capital availability, new markets, infrastructure and supply chains, and political economy — that represent different mechanisms by which a single investment can help move an entire technology category forward.
For cost reduction, for example, an investor might ask how likely it is that the project will reduce the cost of future deployments through learning by doing or economies of scale. If it’s a first-of-a-kind project, the answer is likely yes. For capital availability, they might look at whether the investment will de-risk the technology. Goldman praised Amazon’s early investment in Rivian delivery vans — not just because it took gas-powered Amazon vans off the road, but because it also spurred other automakers and major shippers such as Walmart and GM to follow suit.
“While the Amazon-Rivian deal wasn’t 100% responsible for it, it certainly was a huge signal to the market that there was safety in solving this last mile delivery problem,” he said.
The Rhodium report outlines a method investors can use to score and weight the various attributes and combine them with the technology factor score to reach a final “acceleration factor” score.
In an accompanying report, Rhodium researchers used the framework to compare a number of different options for powering data centers in the U.S. It’s a high-level assessment — i.e. it doesn’t consider project-specific acceleration attributes — but it provides a rough hierarchy of the arrangements that accelerate the energy transition the most against those that do the most harm. At the top of the list is a grid-connected data center that signs a power purchase agreement with a clean, firm generator, such as a nuclear or geothermal plant. At the bottom, with a negative score indicating it would actually hinder progress relative to a regular grid connection, is an off-grid data center powered entirely by natural gas.
Of course, hyperscalers prioritizing speed to power are unlikely to wait around for a nuclear plant to get built. But there are plenty of options between that and behind the meter gas. An off-grid data center that builds enough renewables and batteries for 95% of its electricity needs and relies on gas backup scores higher than a grid-connected project that buys spot market renewable energy certificates.
“Different data center power configurations can have a meaningfully different impact on the transition, even if you’re looking at things that might on the surface seem relatively similar,” Michael Delgado, a partner at Rhodium, told me.
For now, the Transition Acceleration Framework is just that — a framework. Rhodium is piloting it with Generate and CalSTRS, as well as some additional partners, conducting bespoke assessments or their portfolios and projects. The hope is that it could eventually inform not just individual investment decisions or portfolio analyses but regulations and policy packages.
“This is an open method that we’re trying to put out there and get feedback on from the investment and philanthropic and policy world,” Delgado said.
The question is whether he still has a choice.
The United States has resumed bombing Iran, the U.S. military’s regional command announced on Wednesday. The United States also bombed more than 80 sites on Tuesday, including radar and air defense facilities, but the new set of targets is more expansive.
President Trump declared on Wednesday that the ceasefire between the two countries is dead. Yet he also suggested that an extended war isn’t on the table. “We’re not looking for long term,” he said at the NATO Summit in Turkey. “Anything that happens is going to be over very quickly … and will only make it safer, including for oil.”
Such a statement surely reflects the president’s awareness that his war isn’t very popular among Americans. But does he have any leverage anymore over how long the war lasts? When Trump okayed the interim Iran ceasefire in June, he said that Iran would not toll oil and gas tankers passing through the Strait of Hormuz. Since then, Iran and Oman have started setting up the infrastructure to do just that. That discrepancy may have been the ceasefire’s doom: The truce broke down after Iran fired missiles at oil and natural gas tankers that were allegedly not using its approved route through the strait. (Iran has said that its preferred route through the waterway is the “only safe passage.”)
American officials have said that restoring freedom of navigation through the Strait of Hormuz is one of their goals in ending — and now, resuming — the war. But the strait was open to all before the war began; Iran only shuttered it after the United States and Israel began bombing in February. Yet now that Iran has learned how easily it can close the strait and keep it closed, it has a new weapon to wield over the American and European economies.
And what of the country’s nuclear program? Back in March, it allegedly didn’t play into the calculus, partly because President Trump claimed the U.S. had destroyed the program in 2025. Instead, Secretary of State Marco Rubio said that the president had no choice but to enter the new conflict because Israel was already going to bomb Iran, and since the Islamic Republic would respond by targeting American bases in the Middle East, the United States might as well strike first. A day later, President Trump changed the story, saying that Iran was already planning to bomb U.S. military bases, which forced pre-emptive action on America and Israel’s part.
Yet by April 1, the president had justified the war to the American people by citing Iran’s nuclear program more than 20 times. “For years, everyone has said that Iran cannot have nuclear weapons. But in the end, those are just words, if you’re not willing to take action when the time comes,” he said. The new conflict had obliterated the country’s navy, defense industrial base, and ability to produce missiles, he said. Yet Iran — partly thanks to its small, cheap drones — was able to keep the strait closed for another two months.
What does all of this mean for energy and decarbonization? More expensive fossil fuels. The global crude benchmark Brent surged to $80 a barrel today, while West Texas Intermediate surpassed $74, bringing both to roughly the same level as when the June ceasefire was first announced. Researchers at Brown University estimate that Americans have paid $60 billion — or roughly $500 per household — more for gasoline and diesel than they would have had the conflict never happened.
If this stage of the war doesn’t go “long term,” as Trump hopes, then at least the world will have a little more oil than anticipated to work with, as stockpiles have risen in recent days. But a new and extended phase of the war threatens a return to the prices seen earlier in the spring — or prices that go even higher, should China decline to tap its reserves this time. One potential early pain point is diesel, which is already expensive because of Ukraine’s strikes on Russian refineries. Costlier fuel will keep encouraging more EV sales in Europe, Asia, and even the United States; high diesel prices in particular will provide a tailwind to the shockingly rapid electrification of China’s trucking sector.
Of course, the war will bring much more besides — more squandered time, more military spending, more human misery. It is the first that Trump might regret most. A conflict the White House joined without much public debate — and once forecast would last “four to six weeks” — now looks likely to eat much of his second term.
Pollution from peaker plants combined with heat and smoke can push summer air quality into the danger zone.
If you ever have to pick a day to stay inside, pick July 5. In cities across the United States, the Fourth of July’s pyrotechnic revelries make the wee hours after Independence Day consistently one of the worst of the year for air quality. Just look at Washington, D.C., which briefly held the distinction of having the world’s most polluted air this past Sunday morning following one of the largest firework displays in history.
But if you have to pick a second day to stay inside, shoot for one during the second half of July, which is the hottest period of the year in the United States. For one thing, it’s just plain miserable out. For another, the country’s 1,000 or so peaking power plants, or “peakers,” are more likely to be operating to meet the energy demands of heavy air-conditioning use, emitting disproportionately high levels of pollution for the electricity they generate.
Peakers are the backup power sources operators run only when demand is at its highest, such as during a heat wave. Peakers are also “probably the dirtiest and most expensive energy on the grid,” Abbe Ramanan, who leads the Phase Out Peakers project at the nonprofit Clean Energy Group, told me. “They tend to burn dirtier fuels, such as oil, and typically have older and less efficient emissions control systems.”
Some 63 million Americans live within a three-mile radius of a peaker, according to a 2023 Clean Energy Group report, where they face health conditions including “significant … increases in estimated rates of hospitalization for asthma, acute respiratory infection, and chronic obstructive pulmonary disease,” all conditions associated with proximity to fossil fuel-fired plants. On top of that, historic redlining practices mean two-thirds of peakers are located in communities with a higher percentage of low-income households than the national average, according to the group’s reporting. And yet peakers also provide life-saving power and AC when a blackout could mean death, such as during last week’s heat wave on the East Coast, making them simultaneously a menace and necessity to maintaining public health, at least with our current grid.
What exactly is peaker plant pollution? How does it appear in the Air Quality Index you might see on your phone? And how do local regulators consider pollution when issuing air quality forecasts? I set out to get answers.
To understand peaker plant pollution, let’s start with a refresher on how air quality alerts work.
The AQI scale runs from 0 to 500 and reflects the local concentrations of five major pollutants: particulate matter, ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Each pollutant has an Environmental Protection Agency-regulated benchmark for what is safe (many of which are set at levels clean air advocates argue are too lax). As concentrations increase, the overall AQI rises to warn first “sensitive groups” and then the general public when to take precautions, such as limiting outdoor activity or wearing a mask. (To learn more about the AQI scale, read my colleague Emily Pontecorvo’s explainer here.)
As do all fossil fuel power plants, peakers release planet-warming carbon dioxide as a byproduct of combustion, along with nitrogen oxides, particulate matter, volatile organic compounds, and other trace toxins that aren’t captured in the AQI, such as heavy metals. Oil and coal-fired power plants also release sulfur dioxide, which creates acid rain; natural gas-fired plants, on the other hand, emit comparatively little.
While NOx is an irritant in its own right, it is, more significantly, a key ingredient in the chemical reaction that creates ozone. When NOx mixes with volatile organic compounds — found in vehicle exhaust, personal care products, and yes, also power plant emissions — on a warm, sunny day, the chemical reaction creates ground-level ozone, which is corrosive enough to scar lung tissue with repeated, prolonged exposure. An expert once helpfully likened it to me as “sunburn on your lungs.” Health researchers have determined that, globally, ozone (also known as smog) causes a million premature deaths every year.
Yes, although it’s not an easy or neat measurement.
Peaker plants are used to rapidly supply electricity to the grid when demand exceeds the baseload capacity. As a result, they run infrequently — only about 5% of the year, or 464 hours per plant, in 2022, per Clean Energy Group’s analysis of 2022 EPA data. Using a stricter definition of peakers, the Government Accountability Office found that the plants represent nearly a fifth of the nation’s potential generating capacity but produce only about a 30th of its overall electricity, mostly due to the time they spend sitting idle.
Power plants use a number of emission control systems to limit emissions of various pollutants. But the EPA has much looser requirements for low-operating peakers, which “may not have effective, if any, emissions control technology,” the GAO writes. When operational, peakers emit an estimated 60 million tons of CO2 per year, with a median NOx emission rate about 6.1 times greater per unit of electricity generated by natural gas-fueled peakers compared to non-peaker gas plants.
“One really big issue with peakers is the emissions control systems are not operating during times when the plant is starting up or shutting down, which means that emissions are just unabated during those times,” Ramanan told me. “And because those plants tend to operate in short bursts, such as during a heat wave, they will start up and shut down more frequently.” Even up to a day beforehand, when the plant is running its test cycle, it might be emitting pollutants even while not actually providing any power.
One 2017 study by University of Wisconsin–Madison researchers found that across the Eastern U.S. from 2007 to 2012, total electricity generation rose by about 4% for every 1-degree Celsius (1.8-degree Fahrenheit) increase in daily summer temperature, with NOx correspondingly up 3.6% and CO2 up 3.3%. Though these numbers aren’t peaker-specific, the plants represent a disproportionate share of the rise since they’re reserved for the hottest, heaviest-load days.
Though the slower rise in NOx suggests “slightly cleaner plants … on average,” the authors write, that is “not completely unexpected, as new natural gas plants are required to have controls installed even as some peaking plants do not.” They note, however, that their data does not fully capture grandfathered-in units, since gas- and oil-fired peakers are allowed non-direct-measurement reporting.
In fact, in Maine and Connecticut, which “use more petroleum for electricity generation than most states in the U.S., primarily as peaking plants deployed on the hottest days,” NOx jumped 33% and 23% per degree Celsius, respectively. Separately, a 2016 study found that peaking plants may have accounted for up to 87% of local particulate matter in the PJM Interconnection during a July 2006 heat wave.
Peaker plant pollution is significant enough that chronic exposure in local communities has measurable health impacts. But how does it factor into summer AQI levels?
My colleague Matthew Zeitlin spoke this week with Margaret LaFarr, the New York State Department of Environmental Conservation’s director of air resources, who told him that peaker plant pollution is “one of the factors we consider” in formulating its air quality forecasts. But because the state’s agency uses modeling to predict when and where air quality will be poor, the granularity of a single peaker just isn’t there. “If we have to have specific information on the emissions, it would not be ready in time for a timely advisory,” LaFarr said.
Ramanan, whose nonprofit has diligently recorded the negative impacts of peakers, concurred that it is “difficult to pinpoint just how much peaker plants contribute to local air pollution because those sorts of studies are just very expensive to do.” Studies that look at disproportionate health impacts, on the other hand, are a little simpler to put together.
Additionally, while the AQI might rise locally near peakers during a heat wave, because of the nature of the scale, it can’t neatly distinguish why. A high ozone reading, for example, might just as easily be due to tailpipe emissions on a hot day; in the New York metro area, vehicles are responsible for an estimated 60% of the air pollution. Meteorological conditions — whether it’s sunny, a key factor in ozone formation, or which way the wind is blowing — obscure the picture. Particulate matter readings could be from a peaker, for example, but they could just as easily be from wildfire smoke.
One way air quality activists like to think about peaker pollution is as a co-occurrence — that is, a compounding pollution on top of already degraded conditions. Hot days tend to be the worst for ozone already, because of the aforementioned tailpipe pollution; peakers, activated to help with the heat-related energy load, then release more ozone-generating emissions at the worst possible time.
While a precise breakdown of the AQI might not be there for peakers, “we know the days that are more conducive to ozone formation generally tend to be those same days where people are cranking up their ACs and there is a higher demand for energy,” LaFarr said.
There is some speculation that cleaner input fuels could help reduce the worst peaker plant emissions. Generally, this is true: The 2017 study by the University of Wisconsin–Madison researchers found that from 1997 to 2015, in Texas, petroleum use in electricity generation dropped 85% and coal dropped 12%, while natural gas increased 57%. As a result, Texas had the lowest level of SO2 sensitivity of any state.
But beyond the existing fuel mixes, fuel switching is not a clean fix for peaker plants. “Burning things like hydrogen and [methane captured from waste processing facilities] don’t actually reduce the air pollution burden in any meaningful way,” Ramanan argued. “Hydrogen in particular tends to actually have extremely high levels of NOx emissions when it’s combusted.”
In Astoria, a neighborhood of New York City, activists opposed retrofitting the local oil-powered peaker plant to run on natural gas because doing so would “lock the state into relying on fossil fuels for decades, fly in the face of the state’s climate law that requires a drastic reduction in carbon emissions by mid-century and continue to pollute in an already overburdened community where many residents are immigrants and live below the poverty line,” Inside Climate News reported. At the same time, doing so would “reduce the state’s greenhouse gas emissions by more than 5 million tons through the year 2035,” per its owner, NRG Energy.
But a third way emerged: New York eventually denied NRG’s permit because it violated the state’s climate law, and the utility subsequently sold the Astoria facility to serve as the converter station for Beacon Wind, a development off the coasts of New York and Massachusetts.
While wind, new transmission, and battery storage all face enormous headwinds in the current political climate — meaning that many peaker plants targeted by activists for retirement are likely to stick around for years yet — advocates remain adamant that a playbook exists for decarbonization. “In terms of replacing one-to-one capacity, we’ve been looking at battery storage even just at peaker plant sites that can be paired with renewables or grid connected batteries,” Ramanan said, adding that “really great work is also being done in terms of virtual power plants and demand reduction — because it’s not just about reducing peak capacity, it’s also reducing the peak overall.”
That raises a final, particularly thorny question: Is air pollution from peaker plants “worth it” if it means being able to run AC?
A 2018 follow-up study by the same team of researchers at the University of Wisconsin–Madison explored a similar question. They found that climate change alone would increase summer mortality related to the smallest airborne particulate pollution by more than 13,500 deaths, and ozone-related mortality by more than 3,500 deaths in a mid-century scenario. AC-driven power sector emissions — full-fleet numbers, albeit disproportionately including peakers — would, on top of that, account for 654 PM 2.5 deaths and 315 ozone deaths, a nearly 5% and 9% increase, respectively, over climate impacts alone.
Researchers credit access to air conditioning in the United States with a 75% decline in deaths, and modeling exercises frequently show that a blackout during a heat wave could realistically result in hundreds of thousands of people needing medical attention. But clean air advocates also point to examples like Astoria, where the denial of a permit to retrofit a peaker plant for slightly better fossil fuels resulted in the grounds being used for a renewable energy source instead.
It’s certainly not an easily replicable process given the current political and economic climate, but it also perhaps suggests a false dichotomy of peakers vs. AC. Affordable power and livable spaces are just two among a host of community needs energy and public health officials must keep in mind.
“It’s not enough to just replace the existing system with renewables and battery storage and have fewer emissions,” Ramanan said. “It also has to be equitable, because otherwise we’re just going to replicate the same issues we’re having now in different ways.”