When nearly two hundred countries around the world signed the Paris Agreement last year, they committed to work together to limit global warming to 2 degrees Celsius, and, ideally, the safer 1.5 degrees Celsius. Those targets had long been a fixture of UN climate negotiations; they were grounded in science, and, theoretically, could be achieved.

But negotiations on climate change halted and resumed for more than two decades before the Paris Agreement was hammered out. And as time has passed, it’s become harder and harder, in practice, to meet the 2 degree target. A new study in the journal Science lays out a blueprint for how the world could still do so — but it wouldn’t be simple.

Under the Paris Agreement, each country laid out a plan for reducing their emissions. But as the authors of the recent study put it, “alarming inconsistencies remain between science-based targets and national commitments.” In other words, even if the world’s governments stick to their agreements, they won’t keep us within 2 degrees Celsius. A separate analysis, by Climate Interactive, finds that if every country that signed the Paris Agreement honors its commitment, the world will warm by 3.4 degrees.

In order to stay within 2 degrees, the researchers find, the world have to radically slash carbon emissions by 2050. And to do that, we’d have to halve emissions every decade from 2020 through 2050. The approximately 40 gigatons of carbon dioxide that humans produce each year will have to become approximately 5 gigatons a year in 2050.

That doesn’t just mean transitioning from coal to cleaner sources of electricity; it means changing how we get around, how we use land for farming and industry, and the extent to which we allow deforestation in developing countries. And, authors of a new study find, it likely means taking carbon out of the atmosphere, something we don’t yet have a good way of doing.

So, as humans are engaged in an unprecedented, war-mobilization-like effort to slash global emissions, new, yet-to-be-discovered technologies would have to come online to suck emissions out of the air, scaling up to cover the 5 gigatons of carbon dioxide humans will still be emitting in 2050, making for net-zero emissions.

All of this would have to happen even as the world population grows — by 2050, the world is projected to be home to 2.5 billion more people than it is today.

The path forward

The starting point is scrapping fossil fuel subsidies — tax breaks and other incentives that governments give to polluters — which the authors of the study estimate are worth between $500 and $600 billion annually, and which the Climate Action Network blames for 36 percent of climate change-causing emissions between 1980 and 2010. In the next few years, China would also have to abandon coal expansion entirely. In order to be on course for 2 degrees Celsius, the authors write, global emissions would have to begin falling by 2020 (they’ve been flat for the last three years), and be cut in half each decade after that.

“Herculean efforts” would have to take place between 2020 and 2030. By the end of that decade, some cities will have to be fossil-fuel free, and the world will have to be on the brink of being coal-free. This, in particular, is significant for the developing world; 1.2 billion people still lack electricity worldwide, and countries such as India have maintained that these people (roughly a quarter of whom live in India) must be connected to the grid as fast as possible, even if that means building new coal power plants.

Meanwhile, between 2020 and 2030, investment in new, clean technologies to change how cities are wired, how aircraft are fueled, and how long batteries last, among other things, would have to increase by an order of magnitude.

Inspired by Moore’s law

The researchers call this decade halving of emissions a “carbon law.” Lead author Johan Rockstrom explains that he was thinking of Moore’s law, which predicted in 1965 that the number of transistors in a computer chip would double every year. However, to make this carbon law a reality, the world would need governments to put in place actual laws. That’s not likely to happen on a global scale at the moment — with the US planning to ignore its commitment under the Paris Agreement, and, perhaps, bail on the deal entirely, the UN is unlikely to up the penalty for nations that don’t meet their emissions goals.

But the infeasibility of this blueprint, in practice, speaks to why having it is important. It underscores the massive shift in thinking that will have to occur for humans to adequately confront the climate crisis we face. Countries have affirmed the 2 degree target in theory, but are not doing nearly enough to hit it in practice.

The study is, in this way, a call to action for people concerned around the world. In a New York Times op-ed, Rockstrom, the lead author of the study, argues that people don’t need to wait for a literal law from their national governments. “A carbon law of halving emissions every decade can be adopted at all levels: for individuals, families, communities, companies, cities and nations. Those with the biggest carbon footprint need to do the most.”

It’s also a call to action for researchers: It underscores the need for rapid advancements in technologies that could remove carbon from the atmosphere. Planting trees can help with this, but to accomplish what Rockstrom’s team calls for, we’d need to double what trees and soils (which also absorb carbon) currently do. These technologies are a gamble. Environmentalists have, at times, discouraged banking on futuristic, carbon-removal technologies because it excuses governments from taking action now, with the tools they have. But, as this research makes clear, with the clock continuing to tick, combatting climate change will require an all-of-the-above approach.