On Earth, stars appear to twinkle in the distance. They’re not just benignly, passively bright, though: In order to emit light as they do, they go through a continual process of nuclear fusion. This is the process whereby the Sun’s hydrogen atoms complete fusion into helium atoms, the result being a tremendous amount of energy, heat, and light. Though our Sun has vast stores to draw from to continue doing this process (it’s 4.5 billion years old after all), those stocks, and therefore its lifespan, are finite. The process, in addition, takes a heavy toll on the Sun in our aged Solar System.
The brightness of the Sun, or its luminosity, is affected by its temperature. That, in turn, is increased by the burning of hydrogen and the internal changes that result. In short, the Sun becoming brighter is bad news for us.
This increase in brightness is very slow. Approximately every 110 million years, the Sun’s luminosity is boosted by about 1%, E.T. Wolf and O.B. Toon cite in a December 2013 Research Letter called “Delayed onset of runaway and moist greenhouse climates for Earth.” While it doesn’t sound like much, the study explains, “Increased solar radiation should at some point trigger moist and then runaway greenhouse climates, ending any hope for continued surface habitability.” This habitability will disappear in approximately 1.5 billion years, and so will the seas.
