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The White House is coordinating a five-year research plan to study ways of modifying the amount of sunlight that reaches the earth to temper the effects of global warming, a process sometimes called solar geoengineering or sunlight reflection.

The research plan will assess climate interventions, including spraying aerosols into the stratosphere to reflect sunlight back into space, and should include goals for research, what’s necessary to analyze the atmosphere, and what impact these kinds of climate interventions may have on the Earth, according to the White House‘s Office of Science and Technology Policy. Congress directed the research plan be produced in its spending plan for 2022, which President Joe Biden signed in March.

Some of the techniques, such as spraying sulfur dioxide into the atmosphere, are known to have harmful effects on the environment and human health. But scientists and climate leaders who are concerned humanity will overshoot its emissions targets say research is important to figure out how to balance these risks against a possibly catastrophic rise in the earth’s temperature.

Getting ready to research a topic is a very preliminary step, but it’s notable the White House is formally engaging with what has largely been seen as the stuff of dystopian fantasy. In Kim Stanley Robinson’s science fiction novel, “The Ministry for the Future,” a heatwave in India kills 20 million people and out of desperation, India decides to implement its own strategy of limiting the sunlight that gets to earth.

Chris Sacca, the founder of climate tech investment fund Lowercarbon Capital, says it’s prudent for the White House to be spearheading the research effort.

“Sunlight reflection has the potential to safeguard the livelihoods of billions of people, and it’s a sign of the White House’s leadership that they’re advancing the research so that any future decisions can be rooted in science not geopolitical brinkmanship,” Sacca told CNBC. (Sacca has donated to support research in the area, but has “zero financial interests beyond philanthropy” in the idea and does not think there should be private business models in the space, he told CNBC.)

Harvard professor David Keith first worked on the topic in 1989, and says it’s being taken much more seriously now. He points to a formal statement of support for research from a group he advises called the Overshoot Commission. The Environmental Defense Fund, the Union of Concerned Scientists, and the Natural Resources Defense Council have also indicated support for research into the topic.

To be clear, nobody is saying sunlight reflection modification is the solution to climate change. Reducing emissions remains the priority.

“You cannot judge what the country does on solar radiation modification without looking at what it is doing in emission reductions, because the priority is emission reductions,” said Janos Pasztor, the executive director of the Carnegie Climate Governance Initiative. “Solar radiation modification will never be a solution to the climate crisis.”

Three ways to reduce sunlight

The idea of sunlight reflection first appeared prominently in a 1965 report to President Lyndon B. Johnson entitled “Restoring the Quality of Our Environment,” Keith told CNBC. The report floated the idea of spreading particles over the ocean at a cost of $100 per square mile. A one percent change in the reflectivity of the earth would cost $500 million per year, which does “not seem excessive,” the report says, “considering the extraordinary economic and human importance of climate.”

The estimated price tag has gone up since then. The current estimate is that it would cost $10 billion per year to run a program that cools the earth by one degree Celsius, said Edward A. Parson, a professor of environmental law at UCLA’s law school. But that is remarkably cheap compared to other climate change mitigation efforts.

A landmark report released in March 2021 from the National Academies of Sciences, Engineering, and Medicine addressed three kinds of solar geoengineering: stratospheric aerosol injection, marine cloud brightening, and cirrus cloud thinning.

Stratospheric aerosol injection would involve flying aircraft into the stratosphere, which is between 10 and 30 miles up, and spraying a fine mist that would hang in the air, reflecting some of the sun’s radiation back into space.

“The stratosphere is calm, and things stay up there for a long time,” Parson told CNBC. “The atmospheric life of stuff that’s injected in the stratosphere is between six months and two years.”

Stratospheric aerosol injection “would immediately take the high end off hot extremes,” Parson said. And also it would “pretty much immediately” slow extreme precipitation events too, he said.

“The top line slogan about stratospheric aerosol injection, which I wrote in a paper more than 10 years ago — but it’s still apt — is fast, cheap, and imperfect. Fast is crucial. Nothing else that we do for climate change is fast. Cheap, it’s so cheap,” Parson told CNBC.

“And it’s not imperfect because we haven’t got it right yet. It’s imperfect because the imperfection is embedded in the way it works. The same reason it’s fast is the reason that it’s imperfect, and there’s no way to get around that.”

One option for an aerosol is sulfur dioxide, the cooling effects of which are well known from volcanic eruptions. The 1991 eruption of Mount Pinatubo, for instance, spewed thousands of tons of sulfur dioxide into the stratosphere, causing global temperatures to drop temporarily by about 1 degree Fahrenheit, according to the U.S. Geological Survey.

A giant volcanic mushroom cloud explodes some 20 kilometers high from Mount Pinatubo above almost deserted US Clark Air Base, on June 12, 1991 followed by another more powerful explosion. The eruption of Mount Pinatubo on June 15, 1991 was the second largest volcanic eruption of the twentieth century.

Arlan Naeg | Afp | Getty Images

There’s also a precedent in factories that burn fossil fuels, especially coal. Coal has some sulfur that oxidizes when burns, creating sulfur dioxide. That sulfur dioxide goes through other chemical reactions and eventually falls to the earth as sulfuric acid in rain. But, during the time that the sulfur pollution sits in the air, it does serve as a kind of insulation from the heat of the sun.

Ironically, as the world reduces coal burning to curb the carbon dioxide emissions that cause global warming, we’ll also be eliminating the sulfur dioxide emissions that mask some of that warming.

“Sulfur pollution that’s coming out of smokestacks right now is masking between a third and a half of the heating signal from the greenhouse gases humans have already emitted into the atmosphere,” Parson said.

In other words, we’ve been doing one form of sunlight reflection for decades already, but in an uncontrolled fashion with terrible warming effects, explains Kelly Wanser, the executive director of SilverLining, an organization promoting research and governance of climate interventions.

“This isn’t something totally new and Frankenstein — we’re already doing it; we’re doing it in the most dirty, unplanned way you could possibly do it, and we don’t understand what we’re doing,” Wanser told CNBC. 

Spraying sulfur in the stratosphere is not the only way of manipulating the amount of sunlight that gets to the earth, and some say it’s not the best option.

“Sulfur dioxide is likely not the best aerosol and is by no means the only technique for this. Cloud brightening is a very promising technique as well, for example,” Sacca told CNBC.

Marine cloud brightening involves increasing the reflectivity of clouds that are relatively close to the surface of the ocean with techniques like spraying sea salt crystals into the air. Marine cloud brightening generally gets less attention than stratospheric aerosol injection because it affects a half dozen to a few dozen miles and would potentially only last hours to days, Parson told CNBC.

Cirrus cloud thinning, the third category addressed in the 2021 report from the National Academies, involves thinning mid-level clouds, between 3.7 and 8.1 miles high, to allow heat to escape from the surface of the earth. It is not technically part of the “solar geoengineering” umbrella category because it does not involve reflecting sunlight, but instead involves increasing the release of thermal radiation.

Known risks to people and the environment

There are significant and well-known risks to some of these techniques — sulfur dioxide aerosol injection in particular.

First, spraying sulfur into the atmosphere will “mess with the ozone chemistry in a way that might delay the recovery of the ozone layer,” Parson told CNBC.

The Montreal Protocol adopted on September 16, 1987, regulates and phases out the use of ozone depleting substances, such as hydrochlorofluorocarbons (HCFCs) which were commonly used in refrigeration and air conditioners, but that healing process is still ongoing.

Also, sulfates injected into the atmosphere eventually come down as acid rain, which affects soil, water reservoirs, and local ecosystems.

Thirdly, the sulfur in the atmosphere forms very fine particulates that cause respiratory illness.

The question, then, is whether these known effects are more or less harmful than the warming they would offset.

“Yes, damaging the ozone is bad, acid deposition is bad, respiratory illness is bad, absolutely. And spraying sulfur in the stratosphere would contribute in the bad direction to all of those effects,” Parson told CNBC. “But you also have to ask, how much and relative to what?”

The sulfur already being emitted from the burning of fossil fuels is already causing environmental damage and is already killing between 10 and 20 million people a year due to respiratory illness, said Parson. “So that’s the way we live already,” he said.

Meanwhile, “the world is getting hotter, and there will be catastrophic impacts for many people in the world,” said Pasztor.

“There’s already too much carbon out there. And even if you stop all emissions today, the global temperature will still be high and will remain high for hundreds of years. So that’s why scientists are saying maybe we need something else, in addition — not instead of — but maybe in addition to everything else that is being done,” he said. “The current action/non action of countries collectively — we are committing millions of people to death. That’s what we’re doing.”

For sunlight reflection technology to become a tool in the climate change mitigation toolbox, awareness among the public and lawmakers has to grow slowly and steadily, according to Tyler Felgenhauer, a researcher at Duke University who studies public policy and risk.

“If it is to rise onto the agenda, it’ll be kind of an evolutionary development where more and more environmental groups are willing to state publicly that they’re for research,” Felgenhauer told CNBC. “We’re arguing it’s not going to be some sort of one big, bad climate event that makes us all suddenly adopt or be open to solar geoengineering — there will be more of a gradual process.”

A man waits for customers displaying fans at his store amid rising temperatures in New Delhi on May 27, 2020. – India is wilting under a heatwave, with the temperature in places reaching 50 degrees Celsius (122 degrees Fahrenheit) and the capital enduring its hottest May day in nearly two decades.

Jewel Samad | Afp | Getty Images

Research it now or be caught off guard later?

Some environmentalists consider sunlight relfection a “moral hazard,” because it offers a relatively easy and inexpensive alternative to doing the work of reducing emissions.

One experiment to study stratospheric aerosols by the Keutsch Group at Harvard was called off in 2021 due to opposition. The experiment would have “threaten the reputation and credibility of the climate leadership Sweden wants and must pursue as the only way to deal effectively with the climate crisis: powerful measures for a rapid and just transition to zero emission societies, 100% renewable energy and shutdown of the fossil fuel industry,” an open letter from opponents said.

But proponents insist that researching sunlight modification technologies should not preclude emissions reduction work.

“Even the people like me who think it’s very important to do research on these things and to develop the capabilities all agree that the urgent top priority for managing climate change is cutting emissions,” Parson told CNBC.

Keith of Harvard agrees. His goal is “simply that we learn more and develop better mechanism[s] for governance,” he told CNBC.

Doing research is also important because many onlookers expect that some country, facing an unprecedented climate disaster, will act unilaterally to will try some version of sunlight modification anyway — even if it hasn’t been carefully studied.

“In my opinion, it’s more than 90 percent likely that within the next 20 years, some major nation wants to do this,” Parson said.

Sacca put the odds even higher.

“The odds are 100 percent that some country pursues sunlight reflection, particularly in the wake of seeing millions of their citizens die from extreme weather,” Sacca told CNBC. “The world will not stand idly by and leaders will feel compelled to take action. Our only hope is that by doing the research now, and in public, the world can collaboratively understand the upsides and best methods for any future project.”  

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CoreWeave is the first cloud provider to deploy Nvidia’s latest AI chips

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CoreWeave is the first cloud provider to deploy Nvidia's latest AI chips

Nvidia CEO Jensen Huang in Taipei, Taiwan, on June 2, 2024.

Ann Wang | Reuters

Nvidia’s Blackwell Ultra chips, the company’s next-generation graphics processor for artificial intelligence, have been commercially deployed at CoreWeave, the companies announced on Thursday.

CoreWeave has received shipments of Dell-built shipments based around Nvidia’s GB300 NVL72 AI systems, Dell said on Thursday. It’s the first cloud provider to install systems based around Blackwell Ultra.

The Blackwell Ultra is Nvidia’s latest chip, expected to ship in volume during the rest of the year. The systems that CoreWeave is installing are liquid-cooled and include 72 Blackwell Ultra GPUs and 36 Nvidia Grace CPUs. The systems are assembled and tested in the U.S., Dell said.

CoreWeave shares rose 6% during trading on Thursday, Dell shares were up about 2% and Nvidia rose less than 2%.

The announcement is a milestone for Nvidia.

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AI developers still clamor for the latest Nvidia chips, which have improvements that make them better for training and deploying models.

Nvidia said Blackwell Ultra can produce 50 times more AI content than its predecessor, Blackwell.

Investors closely watch how Nvidia manages the transition when it announces new AI chips to see if there are production issues or delays. Nvidia CFO Colette Kress said in May that Blackwell Ultra shipments would start in the current quarter.

It’s also a win for CoreWeave, a cloud provider that rents access to Nvidia GPUs to other clouds and AI developers. Although CoreWeave is smaller than the cloud services operated by Amazon, Google, and Microsoft, its ability to offer Nvidia’s latest chips first give it a way to differentiate itself.

CoreWeave historically has a close relationship with Nvidia, which owns a stake in the cloud provider. CoreWeave went public earlier this year, and the stock price has quadrupled since its IPO.

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IPO market gets boost from Circle’s 500% surge, sparking optimism that drought may be ending

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IPO market gets boost from Circle's 500% surge, sparking optimism that drought may be ending

Jeremy Allaire, CEO and co-founder of Circle Internet Group, the issuer of one of the world’s biggest stablecoins, and Circle Internet Group co-founder Sean Neville react as they ring the opening bell, on the day of the company’s IPO, in New York City, U.S., June 5, 2025.

NYSE

For over three years, venture capital firms have been waiting for this moment.

Tech IPOs came to a virtual standstill in early 2022 due to soaring inflation and rising interest rates, while big acquisitions were mostly off the table as increased regulatory scrutiny in the U.S. and Europe turned away potential buyers.

Though it’s too soon to say those days are entirely in the past, the first half of 2025 showed signs of momentum, with June in particular producing much-needed returns for Silicon Valley’s startup financiers. In all, there were five tech IPOs last month, accelerating from a monthly average of two since January, according to data from CB Insights.

Highlighting that group was crypto company Circle, which more than doubled in its New York Stock Exchange debut on June 5, and is now up sixfold from its IPO price for a market cap of $42 billion. The stock got a big boost in mid-June after the Senate passed the GENIUS Act, which would establish a federal framework for U.S. dollar-pegged stablecoins.

Venture firms General Catalyst, Breyer Capital and Accel now own a combined $8 billion worth of Circle stock even after selling a fraction of their holdings in the offering. Silicon Valley stalwarts Greylock, Kleiner Perkins and Sequoia Capital are set to soon profit from Figma’s IPO, after the design software vendor filed its public prospectus on Tuesday. Since its $20 billion acquisition agreement with Adobe was scrapped in late 2023, Figma has been one of the most hotly anticipated IPOs in startup land.

It’s “refreshing and something that we’ve been waiting for for a long time,” said Eric Hippeau, managing partner at early-stage venture firm Lerer Hippeau, regarding the exit environment. “I’m not sure that we are confident that this can be a sustained trend yet, but it’s been very encouraging.”

Another positive sign for the industry the past couple months was the performance of artificial infrastructure provider CoreWeave, which went public in late March. The stock was relatively stagnant for its first month on the market but shot up 170% in May and another 47% in June.

The IPO market is coming back, but it won't be linear, says Lazard CEO Peter Orszag

For venture firms, long considered the lifeblood of risky tech startups, IPOs are essential in order to generate profits for the university endowments, foundations and pension funds that allocate a portion of their capital to the asset class. Without handsome returns, there’s little incentive for limited partners to put money into future funds.

After a record year in 2021, which saw 155 U.S. venture-backed IPOs raise $60.4 billion, according to data from University of Florida finance professor Jay Ritter, every year since has been relatively dismal. There were 13 such offerings in 2022, followed by 18 in 2023 and 30 last year, collectively raising $13.3 billion, Ritter’s data shows.

The slowdown followed the Federal Reserve’s aggressive rate-hiking campaign in 2022, meant to slow crippling inflation. As the lower-growth environment extended into years two and three, venture firms faced increasing pressure to return cash to investors.

‘Backlog of liquidity’

In its 2024 yearbook, the National Venture Capital Association said that even with a 34% increase in U.S. VC exit value last year to $98 billion, that number is 87% below the 2021 peak and less than half the average for the four years from 2017 through 2020. It’s a troubling dynamic for the 58,000 venture-backed companies that have raised a total of $947 billion from investors, according to the annual report, which is produced by the NVCA and PitchBook.

“This backlog of liquidity drought risks creating a ‘zombie company’ cohort — businesses generating operational cash flow but lacking credible exit prospects,” the report said.

Other than Circle, the latest crop of IPOs mostly consists of smaller and lesser-known brands. Health-tech companies Hinge Health and Omada Health are valued at about $3.5 billion and $1 billion, respectively. Etoro, an online trading platform, has a market cap of just over $5 billion. Online banking provider Chime Financial has a higher profile due largely to a years-long marketing blitz and is valued at close to $11.5 billion.

Meanwhile, the highest valued private companies like SpaceX, Stripe and Databricks remain on the sidelines, and AI highfliers OpenAI and Anthropic continue to raise massive amounts of cash with no intention of going public anytime soon.

Still, venture capitalists told CNBC that there are plenty of companies with the financial metrics to be public, and that more of them are readying for the process.

“The IPO market is starting to open and the VC world is cautiously optimistic,” said Rick Heitzmann, a partner at venture firm FirstMark in New York. “We are preparing companies for the next wave of public offerings.”

There are other ways to make money in the meantime. Secondary sales, a process that involves selling private shares to new investors, are on the rise, allowing early employees and investors to get some liquidity.

And then there’s what Mark Zuckerberg is doing, as he tries to position his company at the center of AI innovation and development.

Mark Zuckerberg, chief executive officer of Meta Platforms Inc., during the Meta Connect event on Wednesday, Sept. 25, 2024.

Bloomberg | Bloomberg | Getty Images

Last month, Meta announced a $14 billion bet on Scale AI, taking a 49% stake in the AI startup in exchange for poaching founder Alexandr Wang and a small group of his top engineers. The deal effectively bought out half of the stock owned by investors, leaving them with the opportunity to make money on the rest of their holdings, should a future acquisition or IPO take place.

The deal is a big win for Accel, which led Scale AI’s Series A round in 2017, and is poised to earn more than $2.5 billion in the transaction. Index Ventures led the Series B in 2018, and Peter Thiel’s Founders Fund led the Series C the following year at a valuation of over $1 billion.

Investors now hope the Federal Reserve will move toward a rate-cutting campaign, though the central bank hasn’t committed to one. There’s also ongoing optimism that regulators will make going public less burdensome. Last week, Reuters reported, citing sources familiar with the matter, that U.S. stock exchanges and the SEC have discussed loosening regulations to make IPOs more enticing.

Mike Bellin, who heads consulting firm PwC’s U.S. IPO practice, said he anticipates a diversity of IPOs across sectors in the second half of the year. According to data from PwC, pharma and fintech were among the most active sectors for deals through the end of May.

While the recent trend in IPO activity is an encouraging sign for investors, potential roadblocks remain.

Tariffs and geopolitical uncertainty delayed IPO plans from companies including Klarna and StubHub in April. Neither has provided an update on when they plan to debut.

FirstMark’s Heitzmann said the path forward is “not at all clear,” adding that he wants to see a strong quarter of economic stability and growth before confidently saying that the market is wide open.

Additionally, other than CoreWeave and Circle, recent tech IPOs haven’t had big pops. Hinge Health, Chime and eToro have seen relatively modest gains from their offer price, while Omada Health is down.

But virtually any activity beats what VCs were experiencing the last few years. Overall, Hippeau said recent IPO trends are generally encouraging.

“There’s starting to be kind of light at the end of the tunnel,” Hippeau said.

WATCH: Uptick in VC-backed startup deals

Uptick in VC-backed startup deals

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Tripadvisor stock surges 17% as Starboard Value builds sizable stake in online travel company

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Tripadvisor stock surges 17% as Starboard Value builds sizable stake in online travel company

The Tripadvisor logo is displayed on a tablet.

Mateusz Slodkowski | Sopa Images | Lightrocket | Getty Images

Tripadvisor stock jumped 17% Thursday after Starboard Value revealed a more than 9% stake in the online travel company, according to a securities filing.

The position was valued at about $160 million as of Wednesday’s close.

Tripadvisor shares have been flat since the start of the year after plummeting more than 30% in 2024. Last year, the travel review and booking company said it created a special committee to explore potential options.

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Starboard Value has gained a reputation for pushing for changes such as new CEOs and cost cuts by acquiring significant shares in companies.

Most recently, the firm settled a proxy fight with Autodesk, where it gained two board seats. It has previously pushed for changes at Tinder parent Match Group, pharmaceutical giant Pfizer and Salesforce.

The Wall Street Journal was the first to report the news late Wednesday.

Tripadvisor did not immediately respond to CNBC’s request for comment. Starboard declined to comment on the news.

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