“We’re actually a lot closer than we should be; I can say that with confidence,” says Rob Jackson, an Earth scientist at Stanford and the chair of the Global Carbon Project, which leads the research tracking worldwide emissions levels.

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When climate scientists want to tell a story about the future of the planet, they use a set of four standard scenarios called “representative concentration pathways,” or RCPs. RCPs are ubiquitous in climate science, appearing in virtually any study that uses climate models to investigate the 21st century. They’ve popped up in research about subjects as disparate as southwestern mega-droughts, future immigration flows to Europe, and poor nighttime sleep quality.

Each RCP is assigned a number that describes how the climate will fare in the year 2100. Generally, a higher RCP number describes a scarier fate: It means that humanity emitted more carbon dioxide into the atmosphere during the 21st century, further warming the planet and acidifying the ocean. The best-case scenario is called RCP 2.6. The worst case is RCP 8.5.

“God help us if 8.5 turns out to be the right scenario,” Jackson told me. Under RCP 8.5, the world’s average temperature would rise by 4.9 degrees Celsius, or nearly 9 degrees Fahrenheit. “That’s an inconceivable increase for global temperatures—especially when we think about them being global average temperatures,” he said. “Temperatures will be even higher in the northern latitudes, and higher over land than over the ocean.”

This scenario could still be in the planet’s future, according to Zeke Hausfather, an analyst and climate scientist at Berkeley Earth. Since 2005, total global greenhouse-gas emissions have most closely tracked the RCP 8.5 scenario, he says. “There may be good reasons to be skeptical of RCP 8.5’s late-century values, but observations to-date don’t really give us grounds to exclude it,” he recently wrote.

Even if we avoid RCP 8.5, the less dramatic possibilities still could lead to catastrophic warming. Jackson, the Stanford professor, warned that every emissions scenario that meets the Paris Agreement’s 2-degree Celsius “goal” assumes that humanity will soon develop technology to remove carbon directly from the atmosphere. Such technology has never existed at industrial scales.

“Even some [of the scenarios] for 3 degrees Celsius assume that at some point in the next 50 years, we will have large-scale industrial activities to remove greenhouse gases from the atmosphere,” he said. “It’s a very dangerous game, I think. We’re assuming that this thing we can’t do today will somehow be possible and cheaper in the future. I believe in tech, but I don’t believe in magic.”

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Yet not all data suggest that we’re doomed to RCP 8.5 or equivalent amounts of warming, Hausfather cautions. If you look only at pollution from fossil-fuel burning—and not from land-use events like deforestation—then humanity’s recent record trends closer to RCP 4.5.