Like many political neologisms, “Green New Deal” became de rigueur so fast that it had multiple variations, passionate disciples, critics (some measured, others fierce) and endless namechecks before anyone had said definitively what it meant. The “why” was clear: after decades of the business-as-usual answer to the climate crisis, the environmental movement was more or less united in its conviction that more profound change was needed than awareness-raising and intergovernmental target setting. The precedent was Franklin D Roosevelt’s New Deal of the 1930s, with which he successfully combatted the Great Depression. But does this green version essentially correspond to the bid Jeremy Corbyn made for the Labour leadership in 2015: a national investment bank and 1m jobs in green energy, to simultaneously upskill the population and reach towards a zero-carbon economy? Or is it Alexandria Ocasio-Cortez’s vision of environmental justice wrapped into social justice, the private sector swept up in the enthusiasm of a radical state? Is it Keynesianism – except instead of digging the hole and filling it up, you put a tree in it? Or is it a plan so root-and-branch post-capitalist that none of the old words will do?

These books by Ann Pettifor and Naomi Klein have similar titles and are similar, too, in respect of their urgency. Pettifor delivers a sober, technical but readable account of the framework, as she – among a handful of economists and/or environmentalists, including Richard Murphy (the main architect of Corbyn’s 2015 programme), Larry Elliott (the Guardian’s economics editor) and Jeremy Leggett (solar entrepreneur) laid it out more than a decade ago. It was devised in the wake of the global financial crash, which had two obvious effects: to give it an internationalist perspective, since never more than in 2008 were economists aware of the irrelevance of borders; and to put the focus squarely on systems, rather than individual actors.

Pettifor’s case is pretty straightforward: there is a climate crisis, and it may be too late to avert it, yet to surrender means nihilism. While she directs the occasional weary sideswipe at the climate-change denier, her true enemy is defeatism, and she is very convincing on this: whether or not the planet can be saved, there is no alternative but to try. In such a context money is no object, but it’s not so much “you can’t put a price on our habitat”, rather it is the rallying cry of the heterodox economist, echoing Keynes, Roosevelt, through to US policy wonk Demond Drummer: “we can afford what we can do.” Money is not a finite natural resource, handed us by the mountains or the seas: it is a social construct based on trust and cooperation, created through credit, which is itself backed by the toil of today’s citizens, and the citizens of the future (an idea explored in her last, very readable book, The Production of Money) Deploying examples of the sheer limitlessness of money, when a government really puts its mind to it, Pettifor points to Roosevelt (a fascinating experiment in social ambition, with its own environmental element: over the nine years of the New Deal, 5% of the total male population was engaged in the Civilian Conservation Corps, planting among other things, 2bn trees). She also points to the Marshall plan, to the moon landings – all the classic examples of the hope genre, though given a different spin by climate catastrophe. If we can, as a species, muster all that effort, iconoclasm and single-mindedness just to get to the moon and have a poke about, imagine what we’re capable of when our children’s lives are at stake.

Nothing will be realised, however, without systems change: the problem is not simply that “private financial firms have for decades now displaced governments in the financing of … water, transport, education, housing, environmental services and health”, leaving elected politicians without leverage or agency, and an electorate crying out for strength (hence the inexorable rise of the strongman). It is not just that governments are increasingly impotent in the face of “dollarised financial capitalism shifted off-shore”, powerless before speculative finance which demands high returns on low effort, and therefore is by definition extractive The block on progress is all those things, underpinned by something more fundamental: you cannot, as George Lakoff once spelt out, put profit in a cost benefit analysis against nature. Pettifor has a rare approach, both radical and intricate., and is never more enthusiastic than when she is spelling out the potentially transformative effects of a global transaction tax, or capital controls, or the management of interest rates by public authority, or an alternative to the dollar standard. She can persuade the reader to abandon growth as a goal in the blink of a page, and adopt instead the idea of an economic “Plimsoll line” (what’s the most a vessel can carry before compromising its seaworthiness?). The book’s purpose, though, is more than a manifesto for the climate, while stopping short of fully costed fixes it sets out to show which elements of the world as it is are incompatible with meaningful change, and how manageably (if not necessarily easily) they could be overturned. Quoting the American abolitionist Frederick Douglass, Pettifor notes: “Power concedes nothing without a demand.”

Naomi Klein’s On Fire, a collection of her environmental essays over the past decade, follows the same principles. There are differences in emphasis between the UK’s Green New Deal and the US’s – Britain’s is oriented more internationally, the American version more focused on Roosevelt’s template of transformation through social justice and democratic agency, which by definition is bordered. Fundamentally, though, their prescriptions are the same, and the depth and uniqueness of Klein’s work is in the human beings she brings to the party. Philosophers, flood victims, students, conservationists – she has a reporting style that is rooted in her decades of activism; everybody’s voice is given the same dignity, the same weight. This pluralism alone presents a vast horizon of possibility, a sense of limitless creative energy, all engaged on the same question. None of us is alone, and nor do we have to leave it all to Greta Thunberg. This sweetens what is otherwise quite a bitter pill, a globe that knows its peril but can’t respond. From the floods of Hebden Bridge to the fires of British Columbia, from the oil spill in the Gulf of Mexico to cobalt mines in the Democratic Republic of Congo, the harder you look, the more cause there is to despair.

Klein finds hope not in large motivational assertions, but in the detail: so she quotes the geophysicist Brad Werner, talking an audience through his computer modelled conclusion that “global capitalism had made the depletion of resources so rapid, convenient and barrier-free that ‘earth-human systems’ were becoming dangerously unstable in response”. When pressed by a journalist for a clear answer on the “are we fucked” question, Werner set the jargon aside and replied: “More or less.” Wait, though: there is one source of friction that could slow down and even derail the machine – mass resistance movements. Direct action by environmentalists, say; or hundreds of thousands of school children striking; resistance is not only germane to the dynamic, it is a powerful countervailing force. This isn’t a book about heroes: Klein has an equally keen ear and roving eye for the deniers, the obstructionists, the defeatists, the status quo-ists. She creates vivid and terrifying portraits of the fossil fuel industry in full sail, of the Republican party completely subservient to it (this feels new and Trumpian, but isn’t: Newt Gingrich unveiled the slogan “Drill Here, Drill Now, Pay Less,” in 2008), of the victims of corporate carelessness and catastrophic climate events. Klein can sink your spirits with an analogy: she draws a parallel between the extinction peril of “mismatching”– the process whereby “warming causes animals to fall out of step with a critical food source” – and our own cultural mismatch, where the greatest collective action is required of us just as we are at our most socially atomised. Yet she can lift them again with a metaphor, a parable, the sight of a whale, the feeling of the wind.

Pettifor works extremely hard to describe the mechanisms by which capitalism and corporatism created the climate crisis and, more recently, the degradation of democratic politics. Klein is bolder, tearing through these ideas – the connection between “climate crisis, wealth concentration and racialised violence”, the “violence of othering in a warming world” – on her way to somewhere both more urgent and more nourishing: the sites of resistance, and how each grain might turn into enough sand to stop the machine. These Green New Deals dovetail so well as companion works that they seem designed to be read together. Or is it simply that this is an idea whose time has come – not a moment too soon, and quite possibly too late?

• The Case for the Green New Deal is published by Verso (RRP £12.99); On Fire: The Burning Case for a Green New Deal is published by Allen Lane (RRP £20). To buy copies go to guardianbookshop.com. Free UK p&p call 020-3176 3837.