The window to limit global warming to 1.5°C is closing Illustration: Annelise Capossela/Axios Just 20 out of 400 of the climate scenarios examined in a landmark 2018 United Nations climate report would have a realistic chance of limiting global warming to 1.5°C (2.7°F) above preindustrial levels by 2100, a new study finds. Why it matters: The study, by more than a dozen researchers from around the world, shows that even the scenarios they identified would still need to employ at least one carbon emissions reduction technology at a level they classify as "challenging." The big picture: Many of the scenarios used for the U.N. study relied heavily on employing technologies that pull carbon out of the air and store it permanently in the ground.