This company says it can help cool the planet for $10 billion a year; scientists are raising red flags

One company has a simple-sounding plan to help save the planet: take a food additive and the mineral that makes eggshells hard, produce tiny particles out of them, spray them into the atmosphere and cool the world.

Stardust Solutions, an Israeli-US company founded in 2023 and led by two former Israeli government nuclear physicists, is pushing ahead in the race to develop solar geoengineering , a controversial technology aimed at artificially bringing down global temperatures by dimming the sun.

There are many different solar geoengineering methods, but perhaps the most researched — and the one Stardust focuses on — involves spraying tiny particles into the stratosphere from high-altitude aircraft or balloons to reflect the sun’s energy away from Earth and back into space.

It’s an artificial version of a natural phenomenon. Volcanic eruptions sometimes spew so much sulfur dioxide into the atmosphere it can temporarily lower global temperatures. In 1991, the eruption of Mount Pinatubo in the Philippines injected enough into the atmosphere to produce cooling of 0.9 degrees Fahrenheit (0.5 Celsius) for more than a year.

As humans burn fossil fuels and heat the planet, the question of whether solar geoengineering can and should move from theory to reality is gaining prominence.

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The technology is a “critical tool” for governments to consider as the global thermostat runs terrifyingly hot, said Stardust’s CEO Yanai Yedvab, although he stressed it’s neither a silver bullet for climate change nor a substitute for addressing its root causes.

Many scientists, however, have expressed fears that solar geoengineering could have disastrous global implications, including dramatically altering weather patterns. And some experts are raising red flags that a for-profit company is developing proprietary technology that could have huge and unpredictable repercussions.

“When the whole world is at stake, satisfying the needs of venture capitalists for profits should not enter at all into decisions about what, if anything, should be deployed,” said Raymond Pierrehumbert, professor of planetary physics at the University of Oxford.

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Scientists have been researching solar geoengineering for decades, but private companies are starting to pop up. Of these, Stardust is arguably the most high profile, not least because it’s the best funded, having raised $75 million from investors.

The company was formed in the wake of the pandemic. Yedvab and his co-founder, Amyad Spector, landed on solar geoengineering as they explored ways to help address the climate crisis.

When it comes to spraying particles in the atmosphere, most solar geoengineering research and development focuses on sulfur dioxide, mimicking volcanic eruptions. But sulfur dioxide can have negative impacts, including contributing to acid rain and ozone layer depletion.

Stardust wanted to develop a material “that will be better, will be safer, that could be controlled,” Yedvab said. Earlier this year, it revealed its particle designs in a series of scientific papers, which await peer review.

Arlan Naeg/AFP/Getty Images

The company has produced two particles: One from amorphous silica, commonly used as an anti-caking additive in foods, toothpaste and cosmetics; the other is made from a core of calcium carbonate, the main component in eggshells, surrounded by a shell of amorphous silica.

Both compounds occur naturally, but can be created synthetically. And these are commonly used substances, Yedvab said. Amorphous silica, for example, was released into the New York City subway in 2016, as part of a Department of Homeland Security test designed to simulate the impacts of a potential biological attack. It’s an anecdote that helps highlight how safe silica is considered to be, Yedvab said.

Every million tons of particles would lead to 0.9 degrees Fahrenheit of cooling, and would need be replenished every year, Yedvab said. Each million-ton deployment would cost roughly $10 billion. It’s a lot, he acknowledged, but still a small fraction of the damage climate change-related disasters are already causing .

But experts have raised concerns. In addition to being queasy about private business attempting to alter the climate, some are also concerned about the impacts on global climate and weather, as well as human health.

David Keith, a professor of geophysical sciences at the University of Chicago who is best known for his research on solar geoengineering, said Stardust is “greatly overclaiming to say that they’re confident the risks [of their particles] are lower than with sulfur.” One concern is the “hitchhiker hypothesis” — that particles in the air can pick up metals or other substances that can cause harm when people breathe them in.

Stardust said its particle design takes these risks into account, but whether they will work at scale and how they might behave in the atmosphere is unclear, said Kelly Wanser, executive director of SilverLining, a nonprofit climate research organization.

“Solar geoengineering engages some of the least understood aspects of the climate system,” said Pierrehumbert, adding that no small-scale experiment can indicate how Earth systems would respond to a full-scale deployment.

So far, the company has limited its tests to the lab. Launching outdoor tests is the next step, but history suggests this will be fraught. Plans by Harvard scientists to conduct test flights for solar geoengineering in Arctic Sweden were abandoned in 2021 after intense local opposition. A rogue experiment by US startup Make Sunsets in Mexico in 2022 led the country to ban solar geoengineering experiments.

Stardust, which hopes to start outdoor tests in the next few years, would only run them “under supervision and direct guidance of governments,” Yedvab said. He compared the process to testing life-saving drugs. They would start with very small-scale tests, with clearly defined success criteria, before graduating to larger-scale tests.

The company says it’s already engaging policymakers to try to build a regulatory framework around testing. Decisions on whether the tech is ever deployed belong “solely in governments,” Yedvab said.

Still, Stardust is a for-profit company with a financial incentive in the deployment of this technology, some experts say, and that has raised alarms. “Proprietary technology and profit motives are directly at odds with the transparency needed to legitimize [solar geoengineering] research,” Keith wrote in a blogpost last year.

Sarah Doherty, an associate professor of atmospheric sciences at the University of Washington, who leads a solar geoengineering research team, said “the current science does not support making financial bets on, or driving society toward, specific approaches.”

Yedvab said most groundbreaking technologies benefitting humanity have been made by for-profit companies, albeit often building on academic research.

But the stakes are achingly high. Solar geoengineering could open the door to a host of unintended consequences, including the potential to alter rainfall patterns and shift monsoons, which could have big repercussions for food production, scientists say.

Perhaps most alarming is the prospect of “termination shock.” This is the idea that, once started, solar geoengineering would have to be maintained indefinitely. If stopped suddenly, “the world is then faced with a catastrophic, sudden warming playing out over just a few years,” Pierrehumbert said.

Stardust says its technology can be tuned up or down, meaning deployment can be scaled down gradually. The particles fall out of the atmosphere after roughly a year “so the level of cooling remains a continuing, adjustable choice in the hands of governments and termination shock can be avoided,” Yedvab said.

Some remain unconvinced. Deploying the technology would bring “profound systemic uncertainty” and the “potential to destabilize the global climate system further,” a recent study concluded.

This controversial climate solution could be exactly what the planet needs. Or it could be a colossal disaster

Thorny ethical issues also abound, including who gets to choose when and how solar geoengineering is deployed, who pays for it and what happens if some countries benefit while others are harmed.

“I worry that decisions about if, when, and how to deploy solar engineering will not be made by poor countries but rather by rich countries and private investors,” said Chukwumerije Okereke, professor in global governance and public policy at the University of Bristol.

Then there’s the fear this technology will be seized on as a reason not to make deep cuts to planet-heating pollution, which means significantly reducing the amount of fossil fuels we burn.

This is a “valid concern,” said Yedvab, but it should be balanced with what he called “moral imperatives.” Stardust’s argument is that as the impacts of climate change get increasingly severe and deadly, governments must have options.

Solar geoengineering could “buy humanity the decades needed” to address the underlying causes of climate change, Yedvab said. “I believe the real risk is that a decade from now governments will face a decision on whether they need to deploy this option without having properly studied it and having safe options in front of them.”

一家公司提出了一个听起来很简单的拯救地球的计划：利用一种食品添加剂和使蛋壳变硬的矿物质，将它们制成微小的颗粒，然后喷洒到大气中，从而冷却地球。

Stardust Solutions 是一家以色列-美国合资公司，成立于 2023 年，由两位前以色列政府核物理学家领导。该公司正在大力推进太阳地球工程技术的发展，这是一项备受争议的技术，旨在通过减弱太阳光来人为地降低全球气温。

太阳地球工程方法有很多种，但研究最多（也是《星尘》节目重点关注的方法）的方法是利用高空飞机或气球向平流层喷洒微小颗粒，将太阳能量反射回太空。

这是对自然现象的一种人为模拟。火山喷发有时会向大气中喷射大量的二氧化硫，从而暂时降低全球气温。1991年，菲律宾皮纳图博火山喷发，向大气中注入了足够的二氧化硫，导致全球气温下降了0.9华氏度（0.5摄氏度），持续时间超过一年。

随着人类燃烧化石燃料并导致地球变暖，太阳地球工程能否以及是否应该从理论变为现实的问题日益受到关注。

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Stardust 首席执行官 Yanai Yedvab 表示，随着全球气温异常升高，这项技术是各国政府需要考虑的“关键工具”。但他强调，这项技术既不是解决气候变化的灵丹妙药，也不能替代解决气候变化的根本原因。

然而，许多科学家担心，太阳地球工程可能会带来灾难性的全球性后果，包括剧烈改变气候模式。一些专家也发出警告，一家营利性公司正在开发一项专有技术，这项技术可能会产生巨大且难以预料的后果。

“当整个世界都面临危险时，满足风险投资家的利润需求根本不应该影响到是否应该部署任何资源的决策，”牛津大学行星物理学教授雷蒙德·皮埃尔亨伯特说。

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科学家们对太阳地球工程的研究已有数十年之久，但如今私人公司也开始涌现。其中，星尘公司无疑是最引人注目的，这不仅是因为它资金雄厚，还因为它已从投资者那里筹集了7500万美元。

这家公司是在疫情爆发后成立的。耶德瓦布和他的联合创始人艾米亚德·斯佩克特在探索应对气候危机的方法时，最终选择了太阳能地球工程。

在向大气中喷洒颗粒物方面，大多数太阳地球工程研究和开发都集中在二氧化硫上，以模拟火山喷发。但二氧化硫会产生负面影响，包括加剧酸雨和破坏臭氧层。

耶德瓦布表示，星尘公司希望研发一种“性能更优、更安全、更可控”的材料。今年早些时候，该公司在一系列科学论文中公布了其颗粒设计方案，这些论文目前正在等待同行评审。

Arlan Naeg/AFP/Getty Images

该公司生产了两种颗粒：一种是由无定形二氧化硅制成，通常用作食品、牙膏和化妆品中的抗结块添加剂；另一种是由碳酸钙（蛋壳的主要成分）为核心，外层包裹着无定形二氧化硅。

这两种化合物都天然存在，但也可以人工合成。耶德瓦布说，它们都是常用物质。例如，2016年，作为美国国土安全部一项旨在模拟潜在生物袭击影响的测试的一部分，无定形二氧化硅被释放到纽约地铁中。耶德瓦布说，这个例子有助于凸显二氧化硅的安全性。

耶德瓦布表示，每投放一百万吨颗粒物可使气温降低0.9华氏度，而且每年都需要补充。每次投放一百万吨颗粒物大约需要花费100亿美元。他承认，这笔钱数额巨大，但与气候变化相关灾害造成的损失相比，仍然只是九牛一毛。

但专家们对此表示担忧。除了对私营企业试图改变气候感到不安外，一些人还担心这会对全球气候和天气以及人类健康造成影响。

芝加哥大学地球物理科学教授大卫·基思（David Keith）因其在太阳地球工程领域的研究而闻名，他表示，星尘能源公司“夸大其词，声称他们确信其颗粒物的风险低于硫磺”。其中一个担忧是“搭便车假说”——空气中的颗粒物会吸附金属或其他物质，当人们吸入这些物质时，可能会造成危害。

星尘公司表示，其粒子设计考虑到了这些风险，但其能否大规模应用以及在大气中的表现尚不清楚，非营利气候研究组织 SilverLining 的执行董事凯利·万瑟 (Kelly Wanser) 表示。

“太阳地球工程涉及气候系统中一些最不为人知的方面，”皮埃尔亨伯特说，并补充说，任何小规模实验都无法表明地球系统会对全面部署做出怎样的反应。

迄今为止，该公司仅限于实验室测试。开展户外测试是下一步，但历史经验表明，这将充满挑战。哈佛大学科学家原计划在瑞典北极地区进行太阳能地球工程测试飞行，但由于当地民众的强烈反对，该计划于2021年被迫取消。2022年，美国初创公司Make Sunsets在墨西哥进行的一项未经授权的实验，导致该国禁止了太阳能地球工程实验。

星尘公司希望在未来几年内开展户外试验，但耶德瓦布表示，这些试验“必须在政府的监督和直接指导下进行”。他将这一过程比作测试救命药物。他们会先从小规模试验入手，制定明确的成功标准，然后再逐步过渡到更大规模的试验。

该公司表示，他们已开始与政策制定者接洽，试图围绕检测建立监管框架。耶德瓦布表示，这项技术是否最终部署的决定“完全属于政府”。

不过，一些专家指出，星尘公司是一家营利性企业，其部署这项技术存在经济动机，这引发了人们的担忧。基思去年在一篇博客文章中写道：“专有技术和逐利动机与（太阳地球工程）研究合法化所需的透明度直接冲突。”

华盛顿大学大气科学副教授、太阳地球工程研究团队负责人莎拉·多尔蒂表示，“目前的科学并不支持对特定方法进行经济押注，也不支持推动社会采用特定方法。”

耶德瓦布表示，大多数造福人类的突破性技术都是由营利性公司开发的，尽管这些技术往往建立在学术研究的基础上。

但风险极高。科学家表示，太阳地球工程可能会带来一系列意想不到的后果，包括改变降雨模式和季风走向，这可能会对粮食生产产生重大影响。

或许最令人担忧的是“终止冲击”的可能性。这种观点认为，一旦启动太阳地球工程，就必须无限期地维持下去。皮埃尔亨伯特表示，如果突然停止，“世界将面临灾难性的、突发性的升温，而这种升温可能在短短几年内就会发生”。

Stardust公司表示，其技术可以进行调节，这意味着部署规模可以逐步缩减。这些粒子大约一年后会从大气层中沉降，“因此，冷却水平仍然是各国政府可以持续调节的选择，从而避免了最终的崩溃，”Yedvab说道。

仍有人对此持怀疑态度。最近的一项研究得出结论，部署这项技术将带来“深刻的系统性不确定性”以及“进一步破坏全球气候系统稳定性的可能性”。

这项备受争议的气候解决方案或许正是地球所需要的。但也可能带来一场巨大的灾难。

此外，还存在许多棘手的伦理问题，包括谁有权选择何时以及如何部署太阳地球工程，谁来支付费用，以及如果一些国家受益而另一些国家受到损害会发生什么。

“我担心，关于是否、何时以及如何部署太阳能工程的决定，不会由贫穷国家做出，而是由富裕国家和私人投资者做出，”布里斯托尔大学全球治理和公共政策教授楚库梅里耶·奥克雷克说。

此外，还有人担心这项技术会被用来作为不大幅削减导致全球变暖的污染的理由，这意味着大幅减少我们燃烧的化石燃料的数量。

耶德瓦布表示，这是一个“合理的担忧”，但应该与他所谓的“道德责任”相平衡。星尘组织认为，随着气候变化的影响日益严重且致命，各国政府必须有应对之策。

耶德瓦布表示，太阳地球工程或许能为人类“争取几十年时间”，以解决气候变化的根本原因。“我认为真正的风险在于，十年后各国政府将面临是否部署这一方案的抉择，而他们可能并未对此进行充分研究，也没有其他更安全的替代方案。”