In the 2016 presidential debates, the candidates spent less than six minutes discussing the climate crisis. But in the three years since then, the United States has seen record-setting wildfires, floods and hurricanes; a landmark scientific report; and unprecedented youth climate activism — all of which has moved climate change closer to the center of U.S. politics. Poll after poll suggests the climate crisis is a top issue for Democratic primary voters.

In response, all the leading candidates have endorsed the Green New Deal, and most have rolled out detailed climate plans. In fact, the campaign has become a veritable arms race on climate policy: Timelines are accelerated, budgets expanded, more and more boxes are checked off.

To help the public understand these plans in more detail, the youth-led Sunrise Movement called for a climate debate. While their campaign gained traction, the Democratic National Committee voted against it at a meeting last weekend.

However, two news networks — CNN and MSNBC — will hold climate town halls on Wednesday and Sept. 19-20, respectively. These events will not gather all the candidates together to debate the issues. Rather, candidates will appear one by one, meeting with moderators to discuss their plans in greater detail.

Below I describe the big climate ideas from the top three candidates in the polls: Former vice president Joe Biden, Sen. Elizabeth Warren (Mass.) and Sen. Bernie Sanders (I-Vt.). While Sen. Kamala D. Harris (Calif.) and South Bend, Ind., Mayor Pete Buttigieg are also polling above 5 percent, they have not released detailed climate plans.

What would Jay Inslee do?

Washington Gov. Jay Inslee — whose campaign focused on climate change — dropped out of the presidential race two weeks ago. However, his widely lauded climate plan set the bar for all other candidates, with Green New Deal co-sponsor Rep. Alexandria Ocasio-Cortez (D-N.Y.) referring to it as “the gold standard.”

In six detailed documents that stretched across 218 pages, his campaign outlined how the United States could reduce carbon emissions while creating well-paying jobs and supporting environmental justice. When he exited the race, Inslee said his plans were “open source” and encouraged others to try to enact them. We might expect to see other candidates pick up his ideas in the future.

Timelines and targets

Last year, the Intergovernmental Panel on Climate Change (IPCC)’s urgent report said governments must make significant progress on reducing emissions by 2030 to limit warming to 1.5 degrees Celsius. In response, many candidates’ plans include ambitious timetables that aim to make up for four decades of federal inaction.

Biden’s plan targets a 100 percent clean energy economy with net-zero emissions by 2050. Warren, who has released smaller plans rather than one climate policy, has endorsed scientists’ and the Green New Deal’s targets. Late Tuesday, she released a plan that targeted 100 percent clean electricity by 2035, endorsing Inslee’s timelines. Sanders’s plan targets 100 percent renewable energy for electricity and transportation by 2030, with complete decarbonization by 2050. However, some have criticized his ambitious 2030 targets as unrealistic.

But pushing decarbonization at these speeds is extremely difficult and carries political risks. Aggressive climate policies can face backlash from voters, as the French “yellow vest” protests showed, and as I have shown in research on policies pushing rapid renewable energy growth. In a few cases, carbon pricing policies have been rolled back after opponents win elections, as political scientist Matto Mildenberger shows. Policies will not slow climate change unless they are sustained long enough to reduce emissions.

A role for nuclear energy and fossil fuels?

Last year, nuclear energy supplied 55 percent of the United States’ carbon-free electricity. Many energy experts argue that extending safe nuclear plants’ operating licenses is crucial to reducing carbon emissions from electricity. The Union of Concerned Scientists has a report which argues that nuclear plants that operate safely should stay open until they can be replaced by renewable energy and energy efficiency initiatives. When nuclear plants were shut down in Germany, carbon reductions in the electricity sector stalled, even while the country pushed aggressively on renewable energy.

Neither Biden’s nor Warren’s plans specifically mention nuclear energy. Sanders’s plan states it would not extend licenses for nuclear plants.

All three candidates have pledged to eliminate new fossil fuel production on public lands. However, they take different positions on natural gas fracking, which some scientists think is contributing to increasing methane emissions, a potent greenhouse gas. Sanders has committed to banning fracking altogether. Warren has committed to regulating and limiting it. Biden has not explained his position and has been criticized by environmental groups for having a senior adviser tied to the fossil fuel industry.

Support for innovation

Scientists agree tackling climate change will require new and lower-cost technologies: large scale batteries, machines or processes to remove carbon from the air and new solutions enabling heavy industry to operate without emissions. To bring these technologies to market at a competitive cost, the government will need to support research and deployment.

Both Warren and Biden have committed to spending $400 billion on research and development on a wide range of low carbon technologies over 10 years. They have also promised to commit money to deploying technologies: Warren at $1.5 trillion and Biden at $1.3 trillion. Sanders has promised to commit $780 billion to research and development, although to a narrower set of sectors and as a lower proportion of spending in his overall $16 trillion plan.

Scientists also agree we need to develop technologies that can remove carbon from the air and store it, ideally underground. No candidate has focused on how to develop or deploy these so-called negative emissions technologies. The Sanders plan discusses natural ways to remove carbon from the air, but scientists are concerned about how stable these forms of carbon storage would be given that climate change is already weakening forests’ ability to store carbon.

What should you watch for in the climate forums?

In addition to Biden, Warren and Sanders, the September climate forums will feature other candidates, including entrepreneur Andrew Yang and billionaire activist Tom Steyer, who have also made climate change a central part of their campaigns.

Ultimately, candidates’ climate plans serve several ends. They are symbolic tools that enable them to show they understand the planet is in crisis. They are also road maps for what candidates would do about it — some with far more detail than others. Watch for which candidates can discuss their plans’ details and limitations, making a compelling case for climate action to the American public on national television.

Leah C. Stokes (@leahstokes) is an assistant professor of environmental politics at the University of California at Santa Barbara.