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The world’s biggest polluter is also the world’s top generator of renewable energy.

Ahead of President Biden’s meeting with Chinese President Xi Jinping in San Francisco on Wednesday, the U.S. and China released a joint statement that represents a breakthrough in the two countries’ climate change negotiations. Most notably, the Asian superpower has finally agreed to set concrete targets to reduce emissions across its economy.
The statement asserts that the U.S. and China will work together and with other parties at the upcoming United Nations climate summit in Abu Dhabi, known as COP28, to “rise up to one of the greatest challenges of our time for present and future generations of humankind.”
Underlying the summit is a stark reality: The world will not be able to limit global warming to internationally agreed-upon levels if China, the world’s largest producer of greenhouse gases, does not increase its ambition. The country is now responsible for about a third of annual global carbon emissions. China’s combustion of coal alone accounts for 25% of all energy-related emissions in the world.
Yet China is also the world’s top generator of renewable energy and the foremost manufacturer of much of the technology undergirding the transition. Come with me on a tour of the complex, contradictory state of China’s energy transition in eight eye-popping charts.
China’s climate pledges to date have been vague. The country has said its carbon emissions will peak before 2030, for instance, but has not set a firm target for when or at what level — and the target does not apply to other planet-warming gases like methane. But according to an analysis by Climate Action Tracker, under current policies, China’s annual emissions will peak around 2025 and then plateau for the rest of the decade. That’s primarily due to a projection that the country will continue to rely heavily on fossil fuels as its total energy demand grows. But as we’ll see, this is also one of the key uncertainties around China’s transition.
The biggest source of emissions in China is the power sector. More than 60% of its electricity generation came from coal-fired power plants last year. At COP26 in Glasgow, China said it would “phase down coal consumption” beginning in 2026, but unlike the U.S., which hasn’t built a large coal plant in 10 years, China is growing its coal fleet. Last year, the country greenlit the construction of two new coal plants per week on average, according to Global Energy Monitor, and the trend continued into 2023.
China’s coal permitting spree is the result of rising anxieties among leadership over energy security in light of the COVID-19 pandemic, war in Ukraine, and now the Israel-Hamas war, Kevin Tu, a non-resident fellow at Columbia’s Center on Global Energy Policy, told me. He said China “undoubtedly” overemphasized security in its energy decision-making and that these plants were at risk of becoming stranded assets.
But as Cornell University professor and Heatmap contributor Jeremy Wallace wrote earlier this year, China’s coal plants haven’t even been running at full capacity, and are “shifting to a role of backing-up renewables.” The International Energy Agency predicted last month that China will “gradually use its coal-fired power more to provide flexibility and less to deliver bulk energy.”
China may also begin trying to capture the carbon emitted from its coal plants, with the help of the U.S. One of the points of agreement reached this week was an aim to “advance at least 5 large-scale cooperative [carbon capture, utilization, and storage] projects each by 2030.”
Even though China is building coal plants like there’s no tomorrow, the proportion of its overall energy consumption coming from fossil fuels is actually dropping quite rapidly — at a much faster rate than in the U.S. The country has reduced fossil fuels to about 82% of its energy mix, and plans to get no more than 75% of its energy from fossil fuels by 2030.
The analysis by Climate Action Tracker shows China “significantly overachieving” that goal, primarily because the country is building wind and solar farms at a truly wild pace.
China will build more solar generation this year than the U.S. has built, period. The country’s 2023 additions of low-carbon resources — solar, wind, nuclear, and hydroelectric — are enough to meet the annual electricity needs of the entire United Kingdom.
Critics of China’s climate commitments look at the country’s unbelievably fast progress on renewables and argue it could easily raise its ambition. The country will most certainly exceed the 1,200 gigawatts of wind and solar it has outlined in its current policy plans.
China is even doing what has become impossible in much of the Western world and growing its nuclear fleet. “This will be the largest expansion of nuclear capacity in history, by far,” Jacopo Buongiorno, a professor of nuclear science and engineering at MIT, told CNBC recently.
China has already won the race when it comes to manufacturing clean technologies. Even though the U.S. is pouring billions of dollars into building up its own manufacturing capacity, it’s hard to imagine we’ll ever put a real dent in China’s market dominance for lithium-ion battery and solar module production.
It’s much more likely that the U.S. and other developed countries will continue to rely heavily on China for their own energy transitions. Earlier this year, Group of Seven leaders admitted as much when they described their approach to relations with China as “derisking, not decoupling.”
China’s manufacturing prowess could also benefit a far wider swath of the globe. “China has an opportunity to leverage such capabilities to facilitate deploying clean energy globally,” said Gang He, an assistant professor of energy and climate policy at Baruch College, in an email. “Especially in the world's least developed and most vulnerable countries.”
That’s not happening yet. In September 2021, China committed to ending its overseas financing of coal-fired power plants and to support renewable energy development abroad. But while its coal finance came to an abrupt halt, its investment in wind and solar has not gone up accordingly, according to the World Resources Institute.
But in the new joint statement with the U.S., China agreed to “pursue efforts to triple renewable energy capacity globally by 2030” in addition to accelerating the “substitution” of renewables for fossil fuels in their own countries.
How to make sense of all of this?
Earlier this week, CarbonBrief had quite an optimistic take on the data. It found that China’s rate of low-carbon energy expansion is on track to outpace the annual increase in electricity demand — telling a different story than Climate Action Tracker projected about that first key uncertainty I mentioned. This could push emissions “into an extended period of structural decline,” the authors wrote. But it all depends on whether wind and solar interests can overcome China’s powerful coal lobby.
“What China really needs is to conduct some serious institutional reform to make its power system more friendly toward renewables,” Tu told me. “The problem in China is that the coal interest group makes such reform very difficult.”
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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.”