On Sunday night, the UN’s Intergovernmental Panel on Climate Change dropped an urgent report on the state of global warming. Simply put: The laws of the physical universe say that we can keep global warming to 1.5 degrees Celsius above pre-industrial levels, the optimistic goal set out in the Paris Agreement, but we’re quickly running out of time. As in, we may reach that 1.5 in as little as a dozen years at the rate we’re spewing emissions. And the consequences will be disastrous.

To correct course and avoid 1.5 C, or 2.7 degrees Fahrenheit, we’ll need to cut emissions by half before 2030, and go carbon-neutral by 2050, the report says. That gives us three decades to transform our energy production into something unrecognizable, with renewable energy galore combined with carbon capture techniques like the bolstering of forests, and maybe even sucking the stuff out of the atmosphere and trapping it underground. We’ll have to change our behavior as individuals, too. Meaning, we’re looking at unprecedented change, what is essentially the restructuring of civilization.

“The report has sent a very clear message that if we don't act now and have substantial reductions in carbon dioxide emissions over the next decade, we are really making it very challenging to impossible to keep warming below 1.5 degrees,” said the IPCC’s Jim Skea at a press conference announcing the report, a massive survey by almost 100 authors (and 1,000 reviewers) citing 6,000 studies.

The 2015 Paris Agreement included the 1.5 goal at the urging of island nations, which rising seas are threatening to drown. The less ambitious—though still very daunting—goal is 2 degrees.

Which, according to this new report, would be far more ruinous. At 2 degrees, 10 million more people will be at risk of rising seas than at 1.5 degrees. That extra half a degree also means significantly larger populations will be exposed to water shortages. You’re looking at an ever greater loss of biodiversity, worsening storms, ever more people thrust into poverty, and relentlessly shrinking yields for essential crops like rice and maize and wheat.

Basically, a difference of just half a degree may not seem like much when you’re choosing what to wear for the day, but it’s going to make climate change far, far worse, a point this report drives home in exhaustive detail. “It shows that half a degree of global warming does matter and that limiting it to 1.5°C instead of 2°C would avoid several impacts, including increases in heatwaves and hot extremes in most inhabited regions, heavy precipitation in several regions, and droughts in some regions,” says Sonia Seneviratne, a climate change scientist at ETH Zurich. Plus, limiting warming would avoid certain irreversible changes related to sea level rise and the destruction of coral reefs.

“Even more importantly,” Seneviratne adds, “it shows that limiting global warming to 1.5°C is still physically possible and could be in principle achieved, although it requires rapid, far-reaching and unprecedented changes in all aspects of society.”

Still, the outlook is grim. The technological and social change the world needs dwarfs anything that’s come before in history. “It's not a happy report,” says Thanu Yakupitiyage, spokesperson for the climate advocacy group 350.org. “They're reporting on the real needs of the now. We are in the middle of the climate crisis.”

“At the end of the day, what we're talking about is millions of lives at stake,” Yakupitiyage adds. “We're already seeing the ways in which people are impacted by heat waves, by rising sea levels, by wildfires, by hurricanes.”