California hosted the Global Climate Action Summit in San Francisco last week in an effort to galvanize stronger commitments to address climate change in advance of this fall’s critical climate negotiations in Poland.

With President Trump’s 2017 announcement of the intended departure of the United States from the 2015 Paris agreement and news that countries are underperforming on their Paris commitments, the summit was intended to recharge the climate community. Cities, regions and companies would move forward with ambitious commitments to reduce emissions, and then national governments would follow suit.

Nonstate actors can lead, but they need the support of national governments.

What are the prospects for nonstate climate action? Troubled by the slow progress in global climate negotiations, political scientists are studying this in depth. The research shows that subnational and nonstate action has promise but cannot replace ambitious national policy as the cornerstone of climate mitigation.

What these actors can do is experiment with new approaches, bypass thorny national politics and devise policies that fit the local context. When local actors have enough market power, as in the case of California, national governments may follow suit to avoid conflicting policies and regulations.

That’s precisely how the first U.S. vehicle emission standards emerged in 1968, following California’s lead in 1966. Similarly, large nonstate actors can create markets for new technologies. Denmark’s wind turbine exports found a crucial early customer in California starting in the 1970s.

Here’s what subnational and nonstate actors can’t do: Make others take action.

No matter how ambitious California’s policy is, the state government cannot force neighbors to stop burning coal. In the worst case, nonstate leadership could then face increased use of fossil fuels elsewhere. If California reduces the use of fossil fuels and their market price decreases, others could respond by consuming more.

A new Yale University study supports these insights. It sought to assess how far subnational and private actions could reduce emissions in nine high-emitting polities, including the United States, the European Union, China and India. As part of the effort, the researchers assessed how far these commitments would go to meet the U.S. emissions reductions targets under the 2015 Paris agreement.

The Obama administration’s commitment in Paris was to reduce U.S. emissions 26 to 28 percent below 2005 levels by 2025. Recall that the Paris agreement was a marked departure from previous climate agreements in that the pledges were voluntary country-determined targets of intent.

With the Trump administration determined to roll back many of the Obama-era climate commitments, efforts by others to pick up the slack at the state/municipal levels and in the private sector would signal that the loss of federal momentum is not as consequential as many fear.

The Yale study found that if the subnational and private commitments were fully implemented, global emissions in 2030 would be about one-third lower than just with government policies. And actions by subnational actors and the private sector in the United States could fulfill about 50 percent of the United States’ Paris commitment.

Is this reason to celebrate subnational and nonstate power? Not exactly. 

Some climate policy analysts, such as Tom Hale of Oxford University, see these nonstate and subnational commitments as signaling a new dawn in the upsurge of climate action at all levels of society.

The Yale study’s lead author, Angel Hsu, is less sanguine. From her perspective, the groundswell of nonstate and subnational climate commitments cannot fully compensate for inadequate efforts by states — or the Trump policy rollbacks that affect climate change.

A case in point is forestry. In the Yale report, reducing deforestation is the single most important nonstate initiative to reduce emissions. But in key countries, notably Brazil, measures to combat deforestation are first and foremost the national government’s responsibility.

Under President Luiz Inácio Lula da Silva’s tenure, the Brazilian government directly intervened in Amazonian municipalities to detect and penalize illegal forest clearing. Subnational and private actors had neither the motivation nor the means to protect the rain forest from deforestation. This means the single most important nonstate initiative will likely fail without ambitious national support.

What happened in San Francisco?

There were hopes that national leaders would make new ambitious climate commitments, but the gathering served more for CEOs, governors, mayors and leaders in civil society to share what they are doing in the private sector and at the subnational level and make some new commitments.

The event was outgoing Gov. Jerry Brown’s swan song, to showcase California as a climate leader. In late August, the California legislature passed SB100, which mandates that the state derive 100 percent of its electricity from “clean sources” by 2045. With California the fifth- or sixth-largest economy in the world, SB100 might prove to be one of the most consequential pieces of climate legislation to date.

Brown signed SB100 at last week’s summit, which included a number of consequential interim goal posts. Namely, it mandates that, by 2026, 50 percent of California’s energy come from renewables and 60 percent by 2030, up from the previous target of 50 percent. Moreover, the 2045 target is technology neutral. It does not mandate that California’s clean energy sources come simply from renewables. The commitment could be met by nuclear power or new technologies that haven’t been invented yet.

The Global Climate Action Summit had a small formal program but more than 300 side events highlighting efforts to move climate action forward, including the disruptive potential of zero-emission vehicles, refocused initiatives to address emissions from land use and deforestation, and efforts by mayors and businesses to do their part.

Where next for climate policy?

The December COP24 negotiations in Poland are the most important since the 2015 Paris agreement. Poland is where countries are supposed to complete the rules governing the Paris agreement (“the Paris rulebook”). That would encompass everything from how countries should report on their climate actions to how donors will count and mobilize climate finance to aid developing countries. Preparatory negotiations in Bangkok this month left many of these issues unresolved, with tensions of old between developed and developing countries threatening to overshadow Poland.

For climate advocates, the San Francisco summit may have generated some renewed enthusiasm that could carry over to Poland. Time will tell.

Editor’s note: This post has been updated.

Joshua Busby is an associate professor at the LBJ School of Public Affairs at the University of Texas in Austin. His report with Nigel Purvis on “Climate Leadership in Uncertain Times” was released last week by the Atlantic Council. Find him on Twitter @busbyj2.

Johannes Urpelainen is the Prince Sultan bin Abdulaziz Professor of Energy, Resources and Environment at the Johns Hopkins School of Advanced International Studies. He is also the founding director of the Initiative for Sustainable Energy Policy. He tweets @jurpelai.