Good news—we have extra time before the Sun ends life on Earth

The difference between the scenarios is based on extreme views of the temperature/carbon relationship described above. That was done in part because the idea that CO2 would eventually fall to very low levels has been challenged recently, based on some evidence of a much weaker relationship between bedrock weathering and global temperature. So in one scenario, the researchers held the planet’s temperature constant (equal to today’s) and let CO2 drop to compensate exactly for the brighter Sun. This is a world where strong weathering acts as a perfect thermostat. In the other scenario, CO2 is instead held constant at a modern value while temperature increases, representing a very weak weathering thermostat. With weak weathering, the world is around 21° C (38° F) warmer 1.5 billion years from now, and it jumps an additional 40° C (72° F) between then and 2 billion years. Even with CO2 remaining at 400 parts per million, those temperatures would wipe out land plants on Earth. Specifically, the physiological limits of most land plants are crossed by 1.68 billion years, and the rest are toast at 1.87 billion. (Boiling off the oceans and losing our water to space wouldn’t be far behind.)