Solar geoengineering is often portrayed as a sort of emergency brake. Something along the lines of Pull in case of climate emergency to scatter light-reflecting particles to bounce sunlight out of the atmosphere and cool the planet.

But it might be less like a simple brake and more like a complicated, entirely unsolved puzzle.

Some researchers are starting to look into how nations or companies would go about trying to cool the planet—and there’s a lot to figure out. My colleague James Temple dug into these engineering challenges in his latest feature story. My biggest takeaway? This all might be a lot harder than I thought.

I’ll admit, I’ve always thought of geoengineering as a relatively low-tech solution. That’s partly because over the years we’ve seen some companies do their own low-cost guerrilla “experiments,” tossing balloons up into the atmosphere and claiming to have made some small dent in climate change.

But to actually actively cool the planet in a significant way, and to make sure we understand exactly what effect we’re having, there’s a lot that researchers still need to learn. 

First, there’s the problem of getting up into the atmosphere. Generally, the target for solar geoengineering efforts is the stratosphere, since the air there is drier and more stable, so particles deposited there would stay aloft and move around the planet, lowering temperatures over a wider area and for a longer time.

You can release the particles in balloons, but balloons may not go where you want them to. And at a large scale, you’d be leaving a lot of litter all over the planet. That leaves aircraft, but conventional planes aren’t suited to fly around in the stratosphere. (Commercial aircraft generally fly at around 12 kilometers above the Earth’s surface, while geoengineering would require reaching roughly 20 kilometers.) The air is thinner higher up, so aircraft with massive wings would probably fare better than more conventional designs.

One design, from a startup called Iris Aero, shows just how much rethinking of our current flight technologies might be needed—the plane is almost unsettling in its proportions. Its wings are so long, on a stubby little body. It reminds me of a water strider, those bugs that have super-long legs to scurry around on a pond’s surface.

And that’s just the beginning. There’s also the question of what, exactly, would be best to scatter up in the stratosphere. The idea behind geoengineering comes from volcanoes—after an eruption, sulfuric acid ends up floating around in the atmosphere, and it can temporarily cool the planet. But that chemical is sticky and would be heavy to carry, so scattering some sort of precursor to sulfuric acid would probably be better. Researchers, including some at the University of Chicago, one of the leading institutions in this field, are working to figure out the best formula. 

I’m struck by how complicated this turns out to be, and I’m also left with a big question: As research turns from modeling and simulations to the practical aspects of this incredibly controversial technology, what does it mean to be doing this work?

There are major concerns about what effects might come from large-scale attempts to cool the planet. The effects could be positive for some parts of the globe and negative for others. Established weather patterns, like the monsoon season in South Asia, could shift. There are major questions about what the governance for the use of geoengineering should look like, and who gets to decide whether to go ahead. 

Experts who champion research in geoengineering often draw a line between a desire to support learning more about the technology and a call to deploy it. Many would argue that we should understand it better, so we can make informed decisions.

But to me, there’s a clear difference between atmospheric modeling and detailed engineering work on an aircraft. If there’s public research that essentially amounts to a set of practical instructions, I can’t help but feel like it could enable any number of individual actors or nations to take geoengineering into their own hands. It also might normalize the idea of using the technology. 

Some experts shared concerns along these lines with James, arguing that the shift to practical engineering work requires more oversight. Some called research in this area dangerous.

One alternative perspective I found interesting came from Shuchi Talati, executive director of the nonprofit Alliance for Just Deliberation on Solar Geoengineering.

Rather than further practical research making a slippery slope slipperier, it could have the opposite effect, she told James. “The actual practice of R&D will be a sticky slope, because there will be more real-world problems that come up that we haven’t even thought of yet,” she says. Engineering research could challenge the “idealized notions” of how easy the technology would actually be, she adds.

It’s hard to argue against better understanding potential tools to address climate change. But if we draw a map towards a potential future, it might become difficult to control who follows it. 

This article is from The Spark, MIT Technology Review’s weekly climate newsletter. To receive it in your inbox every Wednesday, sign up here. 

It’s a tale of two nuclear industries.

In China, large reactors are coming together at a stunning pace. The country has nearly doubled its nuclear fleet since 2016, reaching nearly 60 gigawatts of total power capacity. The new facilities are nearly all gigawatt-scale pressurized-water reactors.

Meanwhile, the US has built just two reactors in that time—Unit 3 and Unit 4 at Plant Vogtle in Georgia. Smaller reactors are attracting a lot of excitement and investment, though. A microreactor developer just saw its reactor reach criticality in a new Department of Energy pilot program.

The world is racing to meet rising electricity demand, and many countries are interested in energy sources, like nuclear power, that don’t come with greenhouse-gas emissions. The key question: Which of these strategies will really pay off in terms of getting electrons on the grid quickly?  

Today, the US and France are known as leaders in the nuclear industry. The US has the world’s largest fleet, with France coming in second. France is heavily dependent on nuclear for its grid—about two-thirds of the country’s power comes from nuclear reactors.

But they have hardly added any new reactors to their fleets in recent years. The US can point only to Vogtle, and France connected its latest reactor to the grid in December 2024—the first in over 20 years. 

It’s incredibly difficult to build the massive projects that dominate the nuclear industry today. Up-front investment can run well into the billions, so investors need to wait decades to break even. Designs are complex and can often change during the regulatory process, tacking on cost and time. 

Many are hoping that the key to turning things around in these countries could be smaller reactors.

The idea is that shrinking the footprint of a reactor cuts down the initial investment needed to prove out the new technology. The reactors could even be put together in a factory rather than being built on-site, allowing for a lower price over time.

These smaller reactors are the target of tons of interest and investment in the US, including a new Department of Energy pilot program. The department set a goal last year of having three test reactors reach criticality by July 4, 2026, the nation’s 250th anniversary. (Criticality is the point at which a reactor achieves a self-sustaining chain reaction that can release energy.)

Last week, California-based Antares hit the milestone with its Mark-0 reactor. 

The company plans to eventually build microreactors, designed to produce between 100 kilowatts and 1 megawatt of electricity (large reactors on the grid today are at least 1,000 times that size). The core design is a sodium-cooled reactor, and it uses TRISO fuel, self-contained graphite-coated spheres of a more concentrated fuel than what most reactors use today. 

But there is still a long way to go before it can actually produce power—the Mark-0 doesn’t have any power conversion or heat removal systems. The company plans to produce electricity in late 2027 and deploy in the field by 2028, CEO Jordan Bramble told the Associated Press.

The private sector is interested—and invested—too. Big Tech companies are throwing money at new reactors they hope can help power data centers. 

But look to the other side of the globe, and others are sticking with the established blueprint: China is absolutely churning out large nuclear reactors. Construction started on six new reactors there in 2025, and two more got underway in the first five months of 2026. The country is on course to overtake both the US and the European Union in installed nuclear capacity by 2030.

The speed here is staggering. As of 2024, the average time to build a new reactor in China came in at between five and seven years. The global average is about nine years, and the two most recent reactors in the US took about 15 years.

One key to this speed is standardization: China has set up a uniform project management system to design, license, and build new reactors. They’re built in batches of six or more to take advantage of economies of scale.

It’s one of the ideas meant to give the edge to smaller reactors, but China is working to realize the same benefits for larger projects. A huge amount of government investment is certainly helping.

Larger reactors generally provide more electricity to the grid for a lower price, a key consideration in view of China’s steeply increasing electricity demand. While smaller reactors require less up-front investment than larger ones because of their size, they’ll actually be more expensive per unit of electricity produced. 

That’s not to say China is exclusively focused on big reactors: the country is also expected to see its first operational small modular reactor, the Linglong-1, start sending power to the grid this year.

But looking ahead, it’ll be interesting to see if smaller reactors can help the West keep building new nuclear power. At the moment, with China’s quick progress, it’s looking as if bigger might just be better. 

This article is from The Spark, MIT Technology Review’s weekly climate newsletter. To receive it in your inbox every Wednesday, sign up here. 

Would you take a payment to ramp down your electricity use? Would it change anything if you were doing so to help power a local data center?

Google just signed a new deal to help pay for a virtual power plant (VPP) in the largest power grid in the US. The agreement is with Voltus, a leading VPP and distributed energy resources platform.

Voltus will set up the virtual power plant, grouping together devices like electric vehicles and smart thermostats. It’ll pay customers to participate, and the company will dial back power or use the stored energy during times when the grid is stressed. Google will foot the bill for setting it up, and the extra capacity generated by the project will help run its data centers in the region.

This is one of the most concrete examples so far of a tech giant using a VPP to help meet energy demand for data centers. But there are still some lingering questions about just how far this sort of program can go, and what the limits are.

Last year, it felt as if everyone was talking about data center flexibility. A high-profile study from Duke University found that if data centers agreed to decrease their energy demand for roughly 40 hours per year, a whole bunch of them (about 100 gigawatts’ worth) could come online without making new power plants or transmission equipment necessary.

The underlying reason is that our power grid is designed not for our average energy use, but for the absolute maximum: the brutally hot July evening when everyone is blasting their air conditioners, watching Love Island, and microwaving popcorn. If a data center is willing to refrain from pulling so much power during those high-stress times, the grid can happily support it the rest of the year.

One lingering question here is about incentives: How would you get data centers to agree to this? After all, they might not have a very flexible load, especially now that AI use is more widespread—training a model can easily be delayed or shifted, but customer demand is more immediate. Giving up computing capacity could mean losing revenue.

Regulation is one approach that could work here. One proposal in the US would allow new data centers to come online years sooner if they agree to lower demand when the grid is nearing its max.  And a new Texas law requires large users to switch to backup power or curtail their demand in emergency situations.

Another approach is for data center operators to pay for other people to be flexible.

Voltus announced a new program in September that allows data centers to finance flexibility on their local grid. The company calls it “Bring your own capacity.” Google is now the first named customer taking advantage of this program.

In the new agreement, Voltus will pay people who agree to participate in the virtual power plant. The plant will be part of PJM, the grid that covers much of the US East Coast. The company says it will be able to aggregate up to 100 megawatts of distributed energy resources each year. The plant should be operational in 2027, according to Voltus.

This isn’t Google’s first foray into flexibility; the company has agreements with utilities across the US to limit or shift its own energy demand, which can help free up grid capacity. As the company pointed out in a blog post earlier this year, though, there are limits on how flexible a data center can be, and not every facility will be able to ramp down its power demand.

“There is no one solution for expanding grid capacity and we’re continuing to explore all options, including the many avenues for load flexibility,” said Michael Terrell, Google’s global head of advanced energy, in an emailed statement in response to written questions.

Once again, I’m wondering about incentives here. These companies are asking homes and businesses to be flexible. Will they agree?

A recent study in California looked at local people’s willingness to participate in managed electric-vehicle charging. Essentially, the program pays people to give up control of when they charge their EVs. This is another way to help smooth out electricity demand and ease the burden on the grid.

The problem? Not many people signed up. With no economic incentive, only 1% of EV owners enrolled in managed charging. At $40 per month (about 15% of their power bill), only 4.6% did.

This is a different situation and a different region from the one in which Google is working with Voltus. (It’s worth noting that the companies aren’t sharing how much they plan to pay the participants, which will obviously be a big determinant in participation for this kind of project.) 

But this study shows that even with money on the table, people may not always jump at the chance to cede control of their electricity demand. And it certainly feels relevant that about 70% of Americans oppose AI data centers in their area, according to recent Gallup polling. 

Being flexible sounds like a great idea in theory, and these financed VPPs could provide an immediate route to meeting energy demand. But as we move from idea to implementation, it’ll be interesting to see whether trial runs work as intended.  

This article is from The Spark, MIT Technology Review’s weekly climate newsletter. To receive it in your inbox every Wednesday, sign up here. 

This year, there’s been a wave of notable energy companies going public via IPO in the US.

The solar and battery company Solv Energy went public in February, to the tune of $6 billion. X-energy, which is building small modular nuclear reactors, did the same in April, and its stocks surged on its first day of trading to hit a $11.5 billion market cap. Most recently, the geothermal company Fervo Energy went public in mid-May, and its market cap is now about $12.4 billion.

Those are all success stories in the IPO world. And it certainly doesn’t feel like a coincidence that all these companies are racing to provide electricity in an era of rising demand (partly due to data centers). Let’s take a look at how these firms are doing, what this moment says about the grid, and what’s coming next. 

Let’s start with Fervo Energy, a company we’ve covered a lot over the years that’s working to develop enhanced geothermal energy. (We included it on our 2025 list of Climate Tech Companies to Watch.) While conventional geothermal requires finding specific spots with hot rock, water, and fractures to support a power plant, Fervo essentially uses fracking techniques to create the necessary conditions.

The company was founded in 2017, and it raised about $1.5 billion from investors over the years before its IPO.

Fervo’s first commercial project, Cape Station in Utah, is expected to have a capacity of about 500 megawatts. The first unit is set to start generating power for customers by October and the next two units by January 2027.

The new funding from the IPO could help the company scale. Fervo currently has over 600 megawatts’ worth of binding power purchase agreements. And it has leases for land that could together generate more than 40 gigawatts of electricity. (As of 2024, the entire US geothermal fleet had a capacity of just 4 gigawatts.)

The company also has an eye on cutting construction and drilling costs—its Cape Station plant is expected to cost about $7 per kilowatt, which is cheaper than new nuclear power plants but over twice the expense of building a new natural-gas plant in the US. 

X-energy also aims to provide reliable clean power: it’s part of the wave of next-generation nuclear companies working on small modular reactors. The company is building high-temperature gas-cooled reactors, which flow helium over self-contained pebbles of nuclear fuel. These reactors will each generate 80 megawatts of electricity, less than one-tenth the output of larger ones like Unit 4 at Plant Vogtle in Georgia, the most recent addition to the commercial nuclear fleet in the US.  

X-energy also saw its IPO go well, and prices surged in trading after the initial offering. One interesting tidbit here—the company had previously planned to go public in 2023 but decided against it because of difficult market conditions.

The company is still years away from demonstrating its technology in a commercial project. 

You may recall a story I wrote last year about its effort to build nuclear reactors at the site of a Dow Chemical plant in Texas. The company recently received a key environmental approval for that project, though it’s still waiting for the final green light from the Nuclear Regulatory Commission to start construction.

Finally, Solv Energy builds solar and energy storage projects, mostly for utilities and independent power producers. Solar and batteries are some of the cheapest and easiest technologies to add to the grid, so this one could get a lot of capacity online, quickly. The company already has 21 gigawatts’ worth of projects operational across 35 states.

Many companies in the energy sector are pinning their hopes on the rapid growth in data center construction and operation. The AI boom has transformed the energy landscape, pushing electricity demand higher in a country where it’s been relatively flat for the last decade or so. Solv Energy mentioned data centers over a dozen times in documents filed with the Securities and Exchange Commission before its IPO. 

And Fervo and X-energy are particularly connected to the tech giants driving AI. Google has been a longtime investor in Fervo and also pioneered what it calls its clean transition tariff with the company. Amazon is a client of X-energy as well as an investor; it reportedly owns close to 20% of the company.

Fervo and X-energy are also in industries that occupy a political sweet spot. President Trump and his administration have gone after wind power and other renewables, cutting off existing support and slowing approvals for new projects. Meanwhile, geothermal and particularly nuclear power have kept favor with the federal government and enjoyed continued tax credits and grant funding.

If a few big leaders cash through these IPOs, it could help investors feel more confident about supporting the energy sector, even if that money is concentrated in later-stage ventures like these rather than earlier-stage companies. 

We could see other firms, particularly in nuclear and geothermal, attempt a similar route in the year ahead.

A key thing to watch here will be whether Fervo and X-energy in particular can succeed in scaling up and deploying their technology. If either of these companies stumbles or misses a timeline, it could have ripple effects for those hoping to follow in these very lucrative footsteps. 

This article is from The Spark, MIT Technology Review’s weekly climate newsletter. To receive it in your inbox every Wednesday, sign up here.