Today, it’s not enough to say you believe in climate change. We live in an era of climate emergency that demands radical action. It’s a small step to finally see politicians say this out loud. On May Day, Jeremy Corbyn pushed the UK parliament to declare such an emergency. Just last week, Bernie Sanders, Alexandria Ocasio-Cortez, and Earl Blumenauer introduced a resolution that would declare a national emergency and call for a WWII-style mobilization to address it. It’s no surprise that socialist politicians are the ones out in front, taking this necessary first step.

But we need more than declarations. When it comes to the climate crisis, we have very little time to avoid the worst consequences. Last fall’s IPCC (Intergovernmental Panel on Climate Change) report led many to mobilize around the twelve years timeline, but the reality is that we have to start now to even have a chance to implement what that report describes as “rapid, far-reaching and unprecedented changes in all aspects of society.”

When society implements such massive changes in a short period of time, it’s often called a revolution. Noted climate scientist Kevin Anderson agrees: “When you really look at the numbers . . . the science comes out with, then we’re talking about a complete revolution in our energy system.” What we do between now and 2030 will essentially determine whether we’ll have a livable planet for centuries to come.

This means the next president of the United States — the largest carbon emitter in world history — will be in a unique position to help usher in these transformative changes. Or not. I don’t think it’s hyperbole to say that avoiding catastrophic climate change requires electing the only candidate calling for a political revolution: Bernie Sanders.

Sanders cannot save the climate on his own. But if the climate movement is going to build the kind of power needed to demand the required changes, we must have someone like Sanders in office.

As Sanders says repeatedly on the campaign trail, we need a president with the “guts to stand up to the fossil fuel industry.” This sounds obvious, but as long as we’ve known about the climate crisis, we’ve never had such a president. As many are starting to recognize, actually solving the problem will demand radical action such as nationalizing the fossil fuel industry and placing private utilities under public control. That will be an epic fight.

We need a president that realizes that the solution to the climate crisis starts by saying “stop” to the fossil fuel industry. Sanders told Rachel Maddow this is exactly what his (yet unannounced) climate plan will do: “What it will do is essentially tell the fossil fuel industry that they cannot continue to destroy this planet for the sake of short term profits.”

We already know that on day one, a President Sanders could use executive authority to rejoin the Paris climate treaty, ban fossil fuel extraction on public lands, and reduce emissions by federal government agencies (including the military, whose own emissions would rank them forty-seventh among entire nations). He could also resuscitate — and make much more stringent — the Clean Power Plan, which was based on the legal authority the EPA still has to regulate greenhouse gases by virtue of a 2007 Supreme Court decision.

At the same time, as Sanders also says repeatedly, a President Sanders is not enough. We will not see revolutionary changes on climate unless millions of people build a movement with the disruptive capacity to force those in power to concede to radical demands.

We are already seeing the green shoots of such a movement now — from the Sunrise Movement and Alexandria Ocasio-Cortez’s Green New Deal to the student strike movement. Just imagine how emboldened these movements would become with the election of a class struggle candidate openly “welcoming the hatred” of the fossil fuel industry and calling for a rapid implementation of a Green New Deal.

A President Sanders is not enough to pass a Green New Deal through Congress. We have to set our sights to 2022. Sanders’s strategy to win is based on significantly increasing the turnout of working-class nonvoters by appealing to their desire for a dignified life — a job, health care, education, and a livable planet. Mass turnout is the only electoral answer to Republicans’ continued efforts at voter suppression and gerrymandering.

Let’s imagine Sanders were to succeed in turning out an extra ten to twenty million people from the 137.5 million (61.8 percent) who voted in 2016. Such a turnout could mean a landslide win for Sanders, and could create the conditions for a left blue wave in 2022 to lay the foundation for a Green New Deal in Congress.

Again, a legislative majority will do absolutely nothing unless it is accompanied by a mass working-class movement demanding these changes. This movement can’t revolve around the “single issue” of climate. Although many mainstream commentators lambast the Green New Deal resolution for folding in too many non-climate issues, it is imperative to unite movements around Medicare for All, the fight for $15, revitalizing public education, and the Green New Deal into one large-scale, working-class force.

Of course, the donor base of the Democratic Party would rather burrow more deeply into affluent suburban communities for votes than allow the party to build a durable multiracial working-class majority. In fact, Democratic gains in 2018 were mostly concentrated in affluent communities like Orange County, California. The donor base would rather win by razor-thin margins — or even lose — than cede the party to the left.

To be blunt, it is hard to imagine a world in which we solve climate change while the rich donor base’s grip on the Democratic Party remains intact. Sanders’s grassroots fundraising machine and working-class base are a real threat to these donors.

What about the other candidates? Jay Inslee is making climate the focus of his campaign and has thus far proposed some serious policies, including a phaseout of the fossil fuel industry. But he’s polling at about 1 percent, and, after a lackluster debate performance, his campaign is unlikely to go anywhere. He has also presided over some epic climate defeats as governor of Washington. Carbon tax referendums failed in both 2016 and 2018, the latter of which organized an impressive climate justice coalition.

The current leader in the polls, Joe Biden, has already angered the entire climate community with his demand to find a “middle ground” on climate. In doing so, he is only rehearsing what appears to be his sole strategy: continuing the corporate-friendly governance of his friend President Barack Obama.

After Obama’s soaring rhetoric in his nomination victory speech that “this was the moment when the rise of the oceans began to slow and our planet began to heal,” he left office after eight years with very little progress on climate.

On day one, he could have ordered the EPA to aggressively regulate greenhouse gases. Instead, Obama sought legislation through “bipartisan compromise” and appeasing capital. He got plenty of corporate support behind a toothless and ideologically free-market “cap-and-trade” bill in 2009, but the bill failed in the Senate and was never revisited after the Tea Party victories of 2010.

Before the Deepwater Horizon oil spill in 2010, Obama was even ready to open up the Arctic and the Southeastern seaboard to offshore drilling. In a press event announcing the plan mere weeks before the blowout, he claimed, “It turns out, by the way, that oil rigs today generally don’t cause spills . . . They are technologically very advanced.” To this day, Obama brags about the fact that the United States nearly doubled oil production during his presidency, saying at an event last year, “Suddenly America is the largest oil producer . . . That was me, people . . . Say thank you.”

If we can’t afford another four years of Trump, we also can’t afford another four to eight years of this style of Democratic Party denialism, which claims that climate change can be solved through compromise with corporations and Republicans.

What about Elizabeth Warren? Like pretty much all the candidates, she has endorsed the Green New Deal. And she often takes an encouragingly combative stance toward corporations. But she is more comfortable speaking about Wall Street corruption and monopoly power fleecing ordinary Americans than the fossil fuel industry destroying the planet.

Warren herself has chosen to differentiate herself from Sanders in these terms: “He’s a socialist,” she says, “and I believe in markets.” On the climate issue, we must be especially wary of a fidelity to markets. We’ve wasted the last four decades believing we could solve climate change through smart, “market-based” solutions like a carbon tax or cap-and-trade.

To be fair, Warren’s current announced climate plan includes ambitious spending on green technology and a moratorium on fossil-fuel extraction on public lands (strangely, she decided to dress up this plan in hawkish arguments about “military readiness”).

But here is where the personality, identity, and policy differences between Warren and Sanders should fade into the background. The real question is which candidate’s election is most likely to lead to the kind of mass movement needed to force elites to concede to radical climate demands. Sanders himself has not yet proposed what we need to do in terms of the nationalization and public power mentioned above. But he routinely calls for exactly the kind of movement that might force him to — and exactly the kind that could take on fossil fuel companies.

Warren’s smart plans and fighting spirit make her beloved by many progressives, particularly in the professional class, but it’s questionable whether she could both generate an environmental movement and drive the kind of massive gains in turnout needed to transform the makeup of Congress.

The other question is which candidate is most likely to respond to mass movement demands. While Sanders has spent his lifetime embedded in civil rights, labor, and other mass struggles, Warren is a lawyer-academic and a policy wonk. She would be more likely to seek compromises than side with mass popular demands in the streets.

It’s painfully obvious that a President Sanders will not solve climate change on his own because it is a global problem. We need something like a Global Green New Deal , where the United States leads — and pays for — an international green energy transition in the developing world. Here, again, we need someone willing to take on powerful vested interests.

While the United States has largely fought on behalf of industry in international climate negotiations — through strategies of stalling and outright withdrawal — it must begin to lead international climate policy by calling for bold transformative action everywhere. Bernie Sanders rejoining the Paris Treaty and pledging much more support for the green climate fund would be a good place to start.

The question of the state looms large in the climate crisis. As Naomi Klein points out, it was a case of “bad timing” that we discovered the truth of climate change during the same period of neoliberal hegemony where state power was incapacitated for anything but incarceration and market creation. Yet that period is now ending, and a politics that could actually solve climate change might emerge. Demond Drummer, one of the architects of the Green New Deal, explained the challenge in these terms: “We need to recover some deleted history and remind the American public of what this country is capable of doing.”

Much of the Green New Deal movement is simply about remembering how state power has been mobilized to transform our economy and directly attack powerful economic interests in the past, as with emancipation, World War II, and the New Deal itself.

But we need to recover this deleted history fast, before irreversible changes set in. Bernie Sanders gives us our last fighting chance.