This lukewarm world would still suffer many of the consequences of climate change. There would be more deadly heat waves, more heavy rainstorms, and more intense and frequent droughts. Yet some of the phenomenon’s most catastrophic symptoms, including dozens of feet of sea-level rise and planet-wracking extinctions, might be averted.

The report, in other words, lays out humanity’s last best hope for managing climate change. But it does so against a backdrop of generational failure.

More than a quarter century ago, the countries of the world hammered out the UN Framework Convention on Climate Change. In language signed by President George H. W. Bush and ratified by the Senate, that document—which later gave rise to both the IPCC’s reports and the Paris Agreement—laid out the goal for all of the UN’s future work on climate change. “The ultimate objective,” it said, was to cut greenhouse-gas emissions so as to “prevent dangerous anthropogenic interference with the climate system.”

“Climate scientists have made it abundantly clear, over the past few years, that we’ve already passed that goal. We’ve already dangerously interfered,” says Christopher Field, the director of the Stanford Woods Institute for the Environment, who has worked on previous UN reports but was not involved in this one.

The new report confirms his contention. It finds that the world has already warmed by 1.8 degrees Fahrenheit, or 1 degree Celsius, since humans began sending industrial pollution into the atmosphere. The costs of this warmth can be seen around the world: This decade alone, sweltering heat waves have killed thousands; engorged floods have ravaged cities from Houston to North Carolina; and half of the coral in the Great Barrier Reef has died.

The question is what happens next. “The international community is struggling with how to address the climate challenge … [while] not being able to meet the ultimate objective,” Field told me. “We’ve already seen dangerous interference. Now the question is, How do we deal as effectively as we can with that?”

The new 2.7-degree plan tries to lay out such a strategy. Written by 91 researchers from around the world, it summarizes the findings of more than 6,000 different scientific studies. It argues that humanity must begin rapidly switching away from fossil fuels if it hopes to avoid ecological upheaval. But almost every step of its prescription sits at odds with current policy.

Under the plan, the level of carbon pollution released into the atmosphere every year must begin to fall immediately. (Instead, it hit a record high last year.) By 2030, the world would need to have cut its annual emissions by about half. (Even the Obama administration’s now-canceled climate policies would have cut U.S. emissions only by about a quarter by that year.) By 2050, the world must get 80 percent of its electricity from renewable or nuclear power. (Today, only about 20 percent of electricity comes from those sources.)