In Who Will Build the Ark?, leading radical thinkers debate left alternatives to runaway global heating, capitalist crisis and wider environmental breakdown, clarifying the stakes in today's key disputes between Green New Deal supporters and proponents of degrowth. In a series of landmark texts first published by New Left Review, Herman Daly and Benjamin Kunkel discusses the possibility of an egalitarian, steady-state economy, while Robert Pollin warns against the worldwide slump degrowth could bring and calls instead for a single-issue campaign - 2 per cent of global GDP dedicated to the switch to renewable energy - as the swiftest solution to the emissions crisis. Nancy Fraser envisages an eco-socialist exit from capitalism's multifold crises, while Troy Vettese advocates eco-austerity and half-earth rewilding. Lola Seaton draws out the strategic implications of these contested perspectives, in a set of unavoidable 'green questions'. In the realm of contemporary politics, Alyssa Battistoni writes on the dead-end of COP diplomacy, Cédric Durand asks whether energy shortages will derail the transition away from fossil fuels, and Thomas Meaney compares Green New Deal proposals to the pinched reality of Biden's Inflation Reduction Act. The world's major powers accept the likelihood of dangerous climate change yet seem incapable of averting it. Can radical green models generate the social leverage needed to do so? If not, as Mike Davis puts it in the title essay, 'Who will build the Ark?'