A shorter working week has re-emerged as a prominent subject of political and economic discussion in the U.K. in recent years, with the TUC, the Green Party and Labour taking a reduction of working hours seriously as a policy that could increase workers’ well-being, boost productivity and face the challenges of automation.

In Germany, the IG Metall, Europe’s largest industrial union, led a strike last year that mobilized 1.5 million workers and won the option to individually reduce working time from 35-hours per week to 28-hours per week, while securing the option to return to full-time employment afterwards.

While a shorter working week is often framed as a tool to fix a broken economic model that is working for the few, rather than for the many, the increased interest in working time reductions coincides with the emergence of powerful global movements that highlight another crisis that is facing humanity today: the depletion of resources, the degradation of our natural environments and above all the rapid heating-up of our planet. Here, too, pressing issues of intra- and intergenerational justice emerge, with people in the global south and the poor more likely to suffer the fall-out of an economic system that largely favours the capital-owning class in the global north.

For decades now, the sustainability debate has largely been dominated by calls for ethical consumption, rather than facing the systemic root of the problem: an economic system that prioritizes profit-making over workers’ well-being and even the preservation of the very natural basis of our collective life. To develop a sustainable economic model, it is becoming clear that we need to break with the imperatives imposed by the necessities of capital accumulation (endless “growth”) and find a way to provide a decent standard of living while honouring planetary boundaries. At the same time, our current working time and lifestyle models are deeply intertwined with a fundamentally unsustainable economy, which demands us to endure long commutes due to overpriced housing and eat carbon-intensive, frozen foods since we lack the time to prepare decent quality meals ourselves.

The Intergovernmental Panel on Climate Change has made it clear that limiting global warming to 1.5°c above pre-industrial levels will require rapid, far-reaching and unprecedented changes in all aspects of society; even a quick glimpse into the statistics illustrates just how far-reaching and drastic these changes might need to be.

In this vein, I’ve authored a new paper for the think tank Autonomy that provides a stark thought experiment for us all to consider. Given the current carbon intensity of the economy of the U.K., and given the amount of carbon we are pumping into the atmosphere per hour worked, I estimate that staying within a sustainable carbon budget would require us to cut working times by almost 80 percent, making the new full-time working week a mere nine hours long.

The sheer magnitude of this reduction illustrates that the transformation towards a more sustainable economy needs to go beyond merely cutting back the worst fossil fuel based industries a little: instead, we need to revaluate our economic model and work regime more fundamentally, combining a move towards sustainable energy with a transformation of our transportation systems and a radical reduction in working hours.

Rather than discussing how to maximize profit, the climate crisis forces us to change the conversation and raise the question: provided current levels of carbon intensity of our economies and current levels of productivity, how much work can we actually afford? As my research paper shows, with even the most carbon efficient economies reaching peak sustainable working hours at around a 12 hour working week (given carbon budgets) – a figure close to the 15-hour work week heralded by John Maynard Keynes – we are reminded that a vast expansion of non-work time should be considered less of a luxury and more of an existential urgency.

In this spirit, one concrete and wide-ranging step following the declaration of a climate emergency in the UK could be the immediate introduction of a Four-Day Week as a transitional step: not just to improve the wellbeing and jobs of workers, but also to curb resource usage and greenhouse gas emissions to ensure a decent future for future generations.