People think Earth dies when the Sun becomes a red giant in five billion years — the more likely end is a billion years from now, when a star already 30 percent brighter than at birth pushes CO₂ too l

Key Points:

• The Sun, currently about 4.6 billion years old, is gradually becoming brighter and more luminous, increasing roughly 10% in brightness per billion years during its main-sequence phase.
• Around 1 billion years from now, this increased solar output could push Earth's climate beyond habitable conditions, leading to ocean evaporation, rising water vapor, and the eventual collapse of plant life.
• The decline in atmospheric CO₂ caused by the Sun's brightening will severely impact photosynthetic organisms, particularly C3 plants, disrupting ecosystems and food webs essential for complex life.
• Rising temperatures will trigger a moist greenhouse effect, causing water vapor to reach the upper atmosphere where it is broken down by ultraviolet light, leading to irreversible loss of Earth's water to space.
• In about 5 billion years, the Sun will exhaust its hydrogen core, expand into a red giant, and potentially engulf Earth, which by then will have been uninhabitable for billions of years due to the earlier gradual climate changes.