Carbon dioxide emissions must reach net zero by 2050 in order to keep global warming below 1.5 degrees Celsius according to the “1.5 Degree Report,” compiled by the Intergovernmental Panel on Climate Change (IPCC), a coalition of climate scientists working for the United Nations. For perspective, we emitted over 32 gigatonnes of carbon dioxide last year (a gigatonne is one billion metric tonnes.) The report also claims that national pledges from the 2015 Paris Climate Accord are not enough to meet these targets.

World leaders have 12 years to fundamentally change the structure of our society in order to avoid the most cataclysmic effects of global warming, according to the world’s most important consortium of climate scientists.

In order to reach net zero emissions, according to the report, carbon dioxide use has to fall by 45 percent by 2030, less than 12 years from now. Then, coal use will have to be reduced “substantially” by the middle of the century, and the use of technology that removes carbon from the atmosphere is “unavoidable,” Jim Skea, the Co-Chair of the Working Group III of the IPCC, said at a press conference .

In essence, all of the ways that we create energy, govern industries, construct buildings, cities, and transit systems, and use land for agriculture and resource extraction will have to change. The report even states that the changes that would have to occur ”have no documented historic precedent.”

“Limiting warming to 1.5 degrees is not impossible,” IPCC Chair Hoesung Lee said at a press conference. “But [it] will require unprecedented transitions in all aspects of society.”

If we fail to meet these goals and the earth warms by 2 degrees Celsius, according to the report, hundreds of millions of lives are at stake. Twice as many people would have unreliable access to water as do today. Food shortages in Saharan and Sub-Saharan Africa, the Mediterranean, central Europe, and the South American Amazon will intensify. The range of heat-driven diseases like malaria will spread. Maize, rice, wheat will become about half as productive, and rice and wheat will become less nutritious. But 2 degrees of warming isn’t even a worst-case scenario. If we keep releasing emissions at our current rate, the earth will warm by 4.8 degrees compared to pre-industrial levels by 2100.

The 1.5 Degree Report, which synthesized 6,000 scientific studies and had 133 contributing authors, basically summarizes all of the existing knowledge we have about climate science, and it considers how various policies could impact global warming. The report has been in the works since 2015, when diplomats negotiating the Paris Climate Accord mandated a report to determine exactly how the world can keep global warming below 1.5 degrees Celsius compared to before the industrial revolution . Although the U.S. agreed to the terms of the Accord in 2015 , President Trump said in June 2017 that the U.S. would not recognize the terms of the Accord.

The report also says that limiting individual transportation (such as cars), airplane use, and shipping on a large scale, and improving access to electric transportation, public transit, and non-motor transit (like walking and biking), as well as restoring forests and non-human ecosystems will need to happen at a large scale in order to limit warming to 1.5 degrees. Although the renewable energy sector is growing , it’s not currently growing fast enough to replace the fossil fuel industry by the middle of the century.

These changes that the 1.5 Degree Report considers would monumentally change our society. In order to stop using coal and fossil fuel as a primary energy source by the middle of the century, we will have to transition to using electric, solar, wind, and nuclear power, as well as bioenergy and biofuels (fuels produced from crops like maize.) Carbon capture technology that sucks up carbon dioxide from the atmosphere—which at this point remains an emerging tech that hasn’t been implemented at a large scale—would have to be used heavily in order to compensate for carbon pollution and bring net emissions down to zero.

To be clear, the 1.5 Degree Report is purely a scientific review. It’s up to the governments of the UN to come to enact policy change this December, when the United Nations Framework Convention on Climate Change meet in Poland to negotiate policies.

“Frankly, we’ve delivered a message to the governments,” Skea said at a press conference. “We’ve done our job, we’ve now passed the message on, and it’s their responsibility—having invited us produce this report—to decide if they can gonna act on it.

The big question is whether world leaders are willing to act. Climate historians such as Nathaniel Rich have argued that climate change exposes a limit in the human capacity to envision the future and plan for it. However, there might be a simpler explanation:

1.5 degrees of warming is not an environmental threshold, but a talking point coined in 2009 in order to incentivize political action. But it’s still a devastating amount of warming: At 1.5 degrees of warming compared to 2 degrees of warming, 90 percent of coral reefs will bleach, as opposed to 98 percent. Sea levels will rise by 40 centimeters, as opposed to 50.