Sen. Bernie Sanders, seen in May 2019, has one of the most ambitious climate change plans among 2020 Democratic presidential contenders, but his opponents say it’s unrealistic.

Sen. Bernie Sanders is now the frontrunner for the Democratic nomination in the 2020 presidential election, according to recent nationwide polls.

Since climate change is likely to come up at Wednesday night’s debate in Nevada (where he also leads a recent poll), it’s worth reviewing what Sanders has said about one of his most key issues.

Every Democrat in the February 19 debate in Nevada has put out a proposal, or several, to deal with climate change. That’s not surprising given how important this issue is in the primary, particularly for young voters.

But Sanders has brought it up in almost every debate in a variety of contexts like trade and foreign policy. His climate plan is also the most aggressive among the candidates, with a proposal to invest $16.3 trillion in renewable energy, energy efficiency, and clean transportation, among other areas.

Sanders has also received the endorsement of the Sunrise Movement, a youth-led activist group pushing for aggressive action on climate change. Sunrise is one of the main backers of the Green New Deal, a policy resolution for fighting climate change that aims to ensure a just transition for workers. Sanders has adopted the Green New Deal branding for his own plan to limit rising average temperatures.

As the frontrunner, Sanders will likely face even more scrutiny over what he plans to do in office. From his proposals, his campaign speeches, and his statements on the debate stage, here are five things to know about how Sanders plans to deal with climate change as president.

1) Bernie Sanders wants to go really big and really fast on climate action

Sanders’s $16.3 trillion proposal to make the Green New Deal a reality is the largest among the Democratic contenders. The idea is to generate money from sources like selling energy via power marketing authorities, penalties on polluters, and income taxes from the 20 million new jobs created under the plan.

The timeline is aggressive too. While other candidates are aiming to make the US economy carbon neutral by 2050, Sanders’s Green New Deal aims to decarbonize transportation and power generation, the two largest sources of emissions, by 2030.

That would leave a Sanders administration little time to hit this target. Right now, fossil fuel consumption remains stubbornly high in the US. And Sanders has ruled out using natural gas to replace coal in the interim and wants a drawdown of nuclear energy (more below), making the 2030 timeline all the more difficult to meet.

Sanders’s opponents in the race have criticized his plan as unrealistic, but he countered last month with a letter from 57 climate scientists and researchers proclaiming support for his agenda.

2) Nuclear and natural gas are off the table

While his timeline is ambitious, Sanders is also particular about the tactics he will use. “To get to our goal of 100 percent sustainable energy, we will not rely on any false solutions like nuclear, geoengineering, carbon capture and sequestration, or trash incinerators,” according to his plan.

Sanders has long been skeptical of nuclear power. In 2013, he celebrated the closure of his state’s only nuclear power plant, Vermont Yankee. His plan calls for a halt on nuclear construction and license renewals until a solution for nuclear waste is found.

But nuclear currently provides more than half of zero greenhouse gas emissions energy in the US. Losing this share would push the starting line for decarbonizing electricity far back.

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Sanders has also opposed using natural gas, which produces about half of the carbon emissions of coal. Earlier this month, he introduced legislation to ban fracking, the main technique for extracting natural gas. Natural gas has been a key factor in driving down US greenhouse gas emissions, but opponents point out that it still has a carbon footprint and leaks of methane, a potent greenhouse gas, could outweigh reductions in carbon dioxide.

Nonetheless, these constraints stand to make a difficult political and technical problem even more challenging.

3) Sanders wants criminal prosecution of fossil fuel companies and their leaders

Democrats have become increasingly vocal about naming the fossil fuel industry as the adversary in the fight against climate change. But Sanders has gone even further than most, calling for criminal penalties against coal, oil, and natural gas companies and the people who run them, who knowingly sowed misinformation about climate change.

“[I] will ensure that his Department of Justice and Securities and Exchange Commission investigate these companies and bring suits — both criminal and civil — for any wrongdoing, just as the federal government did with the tobacco industry in the 1980s,” Sanders told Vox.

Fellow presidential contenders Elizabeth Warren, Joe Biden, Tom Steyer, and Mike Bloomberg have also called for criminal penalties on fossil fuel companies.

4) To pass his climate agenda, Sanders wants to change the filibuster, but not eliminate it

The Senate filibuster has thwarted major legislation for years, effectively creating a 60-vote threshold rather than a simple majority. Even with a favorable election outcome, it’s unlikely that Democrats would be able to get around that hurdle under a Sanders administration.

Sanders said his first priority is to get at least 50 behind his proposals like the Green New Deal and Medicare-for-all. “Once we have — and [I] believe it will be sooner than later — a Democratic majority that is prepared to take on the greed and the corruption of the fossil fuel industry and vote for these major reforms in the House and the Senate, we will pass them,” Sanders told Vox. “That means enacting real filibuster reform, including the return to requiring a talking filibuster.”

Should a vote on climate legislation come to a tie, Sanders said he would use the budget reconciliation process to pass the bill. But other than Biden, every other Democratic contender on the debate stage is in favor of getting rid of the legislative filibuster entirely if it proves to be an obstacle.

5) Climate change will be a central element in Sanders’s foreign policy

The United States may be the largest historical emitter of greenhouse gases, but it’s currently just 15 percent of global carbon output. That means the US has to work with other top emitters like China and Brazil to achieve meaningful global action on climate change.

According to Sanders, these facts mean the US needs to lead the world by example and must help poorer countries cope. “The US has for over a century spewed carbon pollution emissions into the atmosphere in order to gain economic standing in the world,” he told Vox. “Therefore, we have an outsized obligation to help less industrialized nations meet their targets while improving quality of life.” At the same time, Sanders wants to end overseas financing of fossil fuel infrastructure through institutions like the Export-Import Bank.

He also wants to use trade as a lever to drive international climate action. During the New Hampshire debate, Sanders said he voted against the USMCA trade agreement between the United States, Mexico, and Canada because it didn’t mention climate change at all.

The US military is also the largest greenhouse gas-emitting institution in the world. Sanders wants to “lead the planet in a wholesale shift away from militarism,” according to his Green New Deal plan, reducing spending on things like having the Navy protect oil shipping routes.

However, it remains extraordinarily difficult to coordinate global action on climate change, and many other world leaders have struggled to bring about tangible agreements despite years of effort. A future Sanders administration would likely have to expend a huge amount of diplomatic effort to lead the world on climate.