By training 192 lasers onto a capsule the size of a peppercorn, U.S. government scientists last week were able to ignite fusion with a net energy gain—a long-sought milestone in the quest for a carbon-free energy future.

But emphasis was on the word “future,” as the team at Lawrence Livermore National Laboratory in California on Tuesday announced the breakthrough in replicating the energy that powers the sun. The successful experiment, which built on generations of prior research, was a pivotal step, they said. But commercialization remained decades away.

“Not six decades, I don’t think, not five decades, which is what we used to say,” said physicist Kim Budil, director of the lab. “I think it’s moving into the foreground and with concerted effort and investment, a few decades of research on the underlying technologies could put us in a position to build a power plant.”

In light of the scientific consensus that the world must drive for net zero carbon emissions within just two decades to avoid the most catastrophic impacts of climate change, the advance has little immediate practical significance in addressing the climate crisis, noted some scientists.

“Getting a lot of q’s about what today’s nuclear fusion breakthrough means for climate,” atmospheric scientist Katharine Hayhoe, professor at Texas Tech University, posted on Twitter. “My answer is: not much.

“I look forward to a world where fusion powers our electricity,” Hayhoe wrote, “but we’re only going to get there if we tackle climate change at scale, today, with the tools available now: efficiency, clean energy, nature + more.”

Still, in a world that has struggled to deploy those solutions, the potential of fusion energy is too great to be ignored, in the view of many climate action advocates, including President Joe Biden. Last spring, Biden announced an initiative to achieve commercial-scale fusion within a decade. As part of that effort, the Department of Energy is weighing proposals for a planned $50 million investment in a future fusion pilot plant.

The breakthrough at Lawrence Livermore’s National Ignition Facility, home of the world’s largest and most powerful laser array, is especially important in light of the decisions now being made on what type of fusion research to fund.

“We need the private sector to get in the game,” said Energy Secretary Jennifer Granholm. “It’s really important that there has been this incredible amount of U.S. public dollars going into this breakthrough. But all of the steps that will be necessary to get this to commercial level will still require both public research and private research.”

She said the breakthrough last week at Lawrence Livermore was an essential step on the pathway, and an achievement that “will go down in the history books.”

The Promise of Star Power

Since the dawn of the nuclear age, there has been hope for harnessing the limitless energy of fusion. Nuclear power plants today rely on fission, the release of energy when the nuclei of certain heavy atoms are split into lighter ones. But enormous energy also can be released when lighter nuclei are fused together to form heavier ones. In theory, fusion would not carry the same safety and radioactive material storage risks as fission. Although some hydrogen isotopes used as fusion fuel are radioactive, they have a far shorter half-life (about 12 years) than the uranium isotopes used in fission (4.5 billion years.)

But strong electrostatic forces normally keep the positively charged hydrogen nuclei from merging. Only the immense gravitational pull of stars like the sun allow the nuclei to fuse. Scientists have focused on two methods for simulating the conditions of a star: the use of strong magnetic fields, or compressing the fusion fuel in a small pellet through the use of particle beams or lasers, known as “inertial confinement.” Magnetic fusion has been ahead in the race to realization. But the researchers at Lawrence Livermore showed the viability of laser fusion.

“A win for either inertial or magnetic confinement is a win for all of us,” said Tammy Ma, leader of the Inertial Fusion Energy (IFE) initiative. “We really just want to see fusion energy happen. Fusion is so incredibly impactful and important for humankind, what we really wanted to do is maximize the potential pathways to success.”

Neither fossil fuel nor clean energy advocates would speculate on the significance of the research breakthrough. A spokesperson for the American Petroleum Institute said the news was beyond the group’s focus and expertise. “Time will tell,” said Gregory Wetstone, president and CEO of the American Council on Renewable Energy. “There’s a long way to go before we’re talking commercial scale, with a real impact on the energy market.”

Sheila Hollis, acting executive director of the United States Energy Association, a nonprofit that includes companies across the energy sector as well as government agencies, said the announcement represented an important step toward developing fusion power, but that “it’s a long road to reach that Nirvana.”

Nicholas Kusnetz contributed to this report.