Four years ago, Shreya Dave left MIT with a doctorate in mechanical engineering and an idea that just might revolutionize the way the world makes chemicals and paper.

She and two colleagues had invented a new filtration system that could slash energy costs for a wide swath of businesses, from paper mills to pharmaceuticals. By doing so, it would also fight climate change, potentially saving more than a billion tons of greenhouse gases each year — nearly the total emissions of Brazil — if used by up to 15 percent of eligible companies worldwide.

Dave’s team launched a start-up in Somerville, Mass., in 2017. But they faced a big problem. Their invention wasn’t flashy like a Tesla, or easy to make, like an app. It needed a lot of early capital and wouldn’t reap immediate profits. It was a classic case of “tough tech” — unappealing to mainstream investors.

After dozens of dead-end fundraising meetings, Dave’s start-up was looking like a charity case. Luckily, a charity was ready to help.

Prime Coalition, a nonprofit organization in Cambridge, Mass., focuses on funding technologies with major potential to cut greenhouse gas emissions. It provided $1 million to Dave’s start-up, Via Separations, which helped the founders triple their staff and develop a prototype they tested in August for the first time in a mill owned by a multinational pulp and paper company.

Since its founding in 2014, Prime has channeled more than $24 million from wealthy donors and big foundations into a portfolio of 10 “tough tech” ventures, making it part of a growing trend that could unleash untapped fortunes to fight one of the world’s most daunting problems.

In 2019, less than 2 percent of $730 billion in global philanthropic giving was spent fighting climate change. But as wildfires in the West and hurricanes in the East turn climate change from an abstraction into a clear and present danger in the United States, that share is starting to rise.

“We see climate change as an existential threat, and the window to address it in a meaningful way is closing,” said John Balbach, director of Impact Investments at the John D. and Catherine T. MacArthur Foundation, which early this year invested $5 million in Prime’s portfolio.

Under the United Nations’ Paris Climate Agreement, 197 countries have pledged to stop average global temperature rise from exceeding 2 degrees Celsius compared to preindustrial levels. That’s the point beyond which scientists say the planet will experience catastrophic, irreversible damage. Even so, many of the technologies needed to make that kind of progress aren’t yet viable, according to a report last summer by the International Energy Agency. More than one-third of the carbon dioxide (CO2) emissions reductions needed would have to come from technologies still at the prototype or demonstration phase, said the report, which called for “urgent efforts to accelerate innovation.”

The biggest challenge for inventors of such potentially world-saving technologies is to cross what tech industry leaders have dubbed the “Valley of Death” between their idea and the marketplace. This is where Prime’s founder, Sarah Kearney, found her mission in 2014.

“We’ve looked at thousands of early-stage companies over the past five years, and there’s no shortage of amazing, dedicated innovators with deep technical knowledge and the courage to pursue their dreams,” said Kearney. “But very few are appropriate for traditional venture capital.”

Just a decade ago, venture capitalists were a lot more eager to invest in technologies to fight climate change. In 2007, Silicon Valley billionaire John Doerr famously wept during a TED talk in which he described discussing climate change with his teenaged daughter. That was the same year that Al Gore’s documentary, “An Inconvenient Truth,” won an Oscar. Gore later became a senior partner at Doerr’s firm, Kleiner Perkins Caufield & Byers, helping to launch a $500 million “Green Growth Fund” aimed not only at making its investors money but to “help speed mass-market adoption of solutions to the world’s climate crisis.”

By 2010, U.S. venture capital investments in “clean tech” had reached nearly $4 billion. Yet that spectacular bubble burst in the wake of the U.S. financial crisis.

Prime and a few related ventures offer new hope for tough tech firms that have since had to scrounge for investments. U.S. philanthropic donations to mitigate climate change nearly doubled over the past five years, from $900 to at least $1.6 billion in 2019, according to research by ClimateWorks Foundation. A small but increasing share of that money is flowing to embryonic firms such as Via Separations. Over the same time, a few relatively new and much larger, for-profit investment groups with a philanthropic tilt are adding to the pool of “patient” money for climate-friendly tech.

Since 2014, Clean Energy Trust in Chicago has invested $5.6 million in philanthropic funds into 34 clean tech start-ups. Rather than return profits to philanthropies and other donors, the fund pours that money into the next crop of companies.

“We’re typically the first to invest after a company steps out from the university,” said CEO Erik Birkerts. A “moonshot” among its investments, he added, is Wright Electric, which is developing technology to electrify aircraft and cut emissions from passenger planes over the next 20 years.

In June, Prime ramped up its own giving with the announcement of a new $52 million fund with 76 investors, many of them new to climate giving. “Our goal is to flip philanthropists from being afraid to go first to being afraid to miss out,” said Kearney. In September, VertueLab, in Portland, Ore., began investing from a smaller but similar Climate Impact Fund, with plans to provide up to $5 million to early-stage clean-tech ventures.

Dwarfing these fledgling nonprofits is Bill Gates’s for-profit Breakthrough Energy Ventures, a $1 billion fund also focused on the toughest kind of climate-mitigation technologies. Gates’s small group of fellow billionaire philanthropists includes Amazon CEO Jeff Bezos, who also owns The Washington Post; former New York mayor and Bloomberg News founder Mike Bloomberg; and Virgin Group’s Richard Branson. The fund might make money on its big bets years from now but prioritizes climate impact over quick profits and is willing and able to take risks unimaginable for conventional investors, with such investments as battery and grid storage technologies and geothermal and fusion energy systems.

Gates’s fund launched in 2015, followed shortly after that by MIT’s The Engine, a $200 million fund for “tough tech” related to sustainable energy, water and food security, and health.”

Prime’s climate-tech success stories include Quidnet Energy, which stores pressurized water for hydropower underground, Connectder, which helps homes with solar power connect to the grid, Lilac Solutions, a less environmentally damaging lithium-mining firm, and Opus 12, which makes products including plastic and fuels out of previously emitted CO2, the most prevalent greenhouse gas.

Each of Prime’s grantees is vetted by a 17-member committee of experts, providing validation for young entrepreneurs whose first job title may be “CEO.” Each must meet three requirements: They must have had trouble attracting other funding, have potential to attract mainstream investors down the line, and be capable of saving at least half a gigaton of greenhouse gas emissions a year by 2050.

“We can’t tinker around with small things,” said Matthew Nordan, Kearney’s business partner.

That’s certainly the spirit of Opus 12, the four-year old brainchild of Kendra Kuhl and Etosha Cave, who met as students at Stanford University. The firm’s CEO, Nicholas Flanders, said its target within the next decade is to save a half-gigaton of carbon equivalent emissions, which he points out is nearly equal to what Shell reports as the total emissions from its refinery and natural gas products. Opus 12 is already lining up customers. Earlier this year it partnered with Daimler to make parts for its luxury cars.

Via Separations’ origin was serendipitous. Dave had written her MIT thesis on a new way to desalinate water, using a membrane made of graphene oxide. Only after graduating did she realize the same filtration system could be used to make paper and chemicals by expending just 10 percent of the energy required by conventional methods, offering hope of reforming two of the world’s most climate-damaging industries.

Thanks in large part to Prime’s timely support, Dave says, her company has recently begun to work with customers.

“There are still plenty of market risks,” she added, “but we’re out of the woods.”

Not all of Prime’s picks have been winners. A reverse-osmosis water technology start-up called Anfiro went out of business in January, even after receiving $1.2 million from Prime. Anfiro had sought to dramatically reduce the energy required to desalinate water. Yet “the technology didn’t quite pan out as we’d hoped,” said CEO and founder Jaime Mateus.

“In the fullness of time I’d expect up to half of the things we invest in to fail,” Nordan said. “That is the nature of this business.”

Prime’s overall record of success keeps Nordan and Kearney hopeful. Kearney gave birth to her third child, Rose, in June, and said she thinks a lot about the fact that Rose will be 30 in the year 2050, the deadline scientists have set for humanity to reach “net zero” greenhouse gas emissions. Given that so many nations still aren’t on track to reach that goal, Kearney admits she sometimes wonders whether her efforts to “mitigate” or cut greenhouse gases make sense, versus trying to adapt to a warming world.

“Prime’s board of directors asks ourselves regularly if it’s prudent to spend on mitigation versus resilience,” Kearney said. “We don’t want to throw good money after bad if we’re past the point of no return. But we don’t think we’re there yet.”

An earlier version of this story included a photo caption that incorrectly stated the paper mill was located in Massachusetts. It is in Chile. It also incorrectly described the goal of the Paris climate agreement, which was to limit average global temperature rise from exceeding 2 degrees Celsius. This story has been updated.