In 2018, the California state legislature set the goal of reaching net-zero carbon emissions by 2045 in the California Climate Crisis Act. In September of 2025, a team of Stanford researchers published a paper in Energy Policy modeling various pathways to decarbonization to meet this goal. 

For Joshua Neutel M.S. ’22, a fifth-year Ph.D. candidate in the civil and environmental engineering department who led the project as part of his graduate program, the work began with a simple question: What would it actually take to reach net zero? 

“[2045] is 20 years away now,” Neutel said. “Let’s have a real conversation about how we are going to do this. How can we get the biggest bang for our buck?”

According to Franklin Orr ’69, professor emeritus of energy resources engineering and co-author of the paper, the basic idea was to look in granular detail at where the emissions come from. The results of the paper break down, which policies and technologies will contribute the most to carbon emission abatement across every energy sector and emissions source in California. 

The team used inputs like the number of technologies per system, their energy usage and the cost of lower-emission alternatives. This detailed approach allowed them to tease out individual technologies, so that “you can get a more granular understanding of the impact potential for each measure separately,” Neutel said. 

The paper concluded that 52% of emissions can be mitigated with commercial technologies already available at scale today, 25% can be mitigated with technologies currently in early stages of commercialization and 23% can be mitigated with technologies in the research stage. 

One striking result, the team emphasized, was the scale of carbon removal the state may need to deploy in order to actually achieve the net-zero goal. “There are always going to be some residual emissions,” said Sarah Saltzer Ph.D. ’92, managing director of the Stanford Center for Carbon Storage and co-author of the paper. “We had to look at negative emissions, things like direct air capture, where you’re literally setting up huge fans and sucking CO₂ out of the air and then injecting it into the subsurface. That’s another way to get rid of emissions from sectors that are just hard to abate.”

Although roadmaps to accomplishing California’s net-zero goal now exist from the government and from this research, the team stressed that the path will be riddled with several political and technological challenges.

“We can make substantial progress with technologies that are readily available,” Neutel said, “However, even in that category, we still are going to have to overcome really big barriers that are mainly logistical [and] political.” 

He pointed to delays in the permitting process for constructing new infrastructure and high upfront costs in investing in new technologies as examples of potential roadblocks. Both Neutel and Saltzer also noted that a key policy assumed in the model — California’s mandate to sell only net zero vehicles by 2035 — currently faces legal challenges. A harder challenge to overcome is changing behavior and social norms. “There are all of us pesky humans,” Orr said, “we don’t always do what’s best for the world.” 

“It’s like trying to rebuild the airplane as you’re flying it, or change the tires as you’re hurtling down the freeway,” Orr said. “You can’t just pause all of the activities that we humans engage in while we quickly rebuild everything.”

Neutel said the team hopes the roadmap will provide valuable insights to both scientists and lawmakers. “Which technologies can hit the ground running because they’re already here and they can make a big difference?” Neutel said. “Which are the ones that we still need to invest in to reduce their costs? Where do we need the most help?”

Despite the many challenges California faces, optimism that the state can meet its goal on time runs strong. “We had an emissions mandate for 2020, which we met and exceeded… we have a rapidly rising share of our transportation fleet coming from electric vehicles now,” said Neutel. “What we do here in California has an impact in other places in the world.” 

Orr added: “Every ton of CO2 we don’t emit is better than the one that we do. So we need to go absolutely as fast as we can.”