The United States’ climate movement emerged unexpectedly. Following a decade of Ronald Reagan and Gordon Gekko singing the praises of the free market, climate catastrophe joined the national conversation in the early 1990s. While warnings about global warming had emerged a generation earlier, the oil and gas industry had spent decades burying the data.

As a result, the climate movement of the ’90s wasn’t much of a movement. Its dominant theory of change assumed that, armed with sufficient data, elite institutions like legislatures, regulatory agencies, and multinational corporations would act in everyone’s best interest. But petrostates, and the U.S. in particular, balked at the idea of decarbonizing their rich, oil-soaked economies and militaries: While environmentalists’ efforts produced the 1997 Kyoto Protocol, the U.S. Senate in 2001 refused to ratify it. The George W. Bush administration, full of oil industry insiders, was disinclined to revive the treaty.

Around six years later, a new youth climate movement sprang up distinct from the big green nonprofits, coordinated in the U.S. by new groups such as 350.org and Energy Action Coalition, and looking more like an actual social movement. But its dominant theory of change still used institutional mechanisms like divestment and attempts to pressure climate negotiators at the United Nations, rather than more grassroots mass politics. In 2009, a coalition of multinational corporations and large environmental nonprofits led an effort to pass the dubious, serpentine Waxman-Markey cap-and-trade bill. While it passed the House of Representatives, it died in the Senate—doomed, some argued, by the absence of grassroots mass movements.

With rapidly rising emissions and swelling urgency, new movements have emerged since the end of Obama’s presidency, branching in two distinct directions. One branch includes organizations like Sunrise Movement, Fridays for Future, Keystone XL and Dakota Access Pipeline groups, 350.org, and Greenpeace (plus Extinction Rebellion in the U.K.). Their strategy involves tactics like occupying legislatures, organizing marches and protests, pushing corporate sustainability and divestment, and nonviolent direct action. The other branch includes the Democratic Socialists of America, unions, and politicians such as Bernie Sanders and Alexandria Ocasio-Cortez. This faction’s strategy is more traditionally leftist, using familiar tactics like organizing strikes and building labor and community power.

Today, the Green New Deal and a shared commitment to grassroots mass politics unite these two branches. Both confront the reality that capitalism, at least as it is currently practiced and defined, cannot decarbonize our economy and society. Both branches are more diverse than ever, more confrontational, and the scope of their vision is finally beginning to match the scope of the problem. The question is whether their current tactics alone are up to the gargantuan task ahead.