“Some say the world will end in fire, some say in ice,” the poet Robert Frost mused in 1920. Frost famously held “with those who favor fire,” and that poetic view surprisingly coincides with mainstream scientific consensus about the end of the world, which states the sun will in some seven billion to eight billion years evolve into a red giant star that will scorch and perhaps even engulf Earth.
Yet when that happens, Earth will already have been dead for billions of years, and will more resemble present-day Venus. As the sun slowly brightens over time on its path to becoming a red giant, it will eventually cross a critical threshold in which its luminosity surpasses our planet’s ability to dissipate absorbed radiation out into space. At that point, somewhere between one billion and three billion years from now, Earth’s surface temperature will steadily rise until the boiling oceans throw a thick blanket of steamy water vapor around the planet. All that water vapor, itself a potent greenhouse gas, will raise temperatures higher still to cook another greenhouse gas, carbon dioxide, out of Earth’s rocks. The end result will be a “runaway greenhouse” in which the planet loses its water to space and bakes beneath a crushing atmosphere of almost pure carbon dioxide.
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