As the sun gets older, it becomes more and more luminous [0], so concentrations of CO2 that didn't cause a runaway greenhouse process in the past may do so in t

As the sun gets older, it becomes more and more luminous [0], so concentrations of CO2 that didn't cause a runaway greenhouse process in the past may do so in the future, because we're getting more sunlight. While this effect is not really noticeable when looking at recent history, once you start going back millions or billions of years it starts to become significant. [0] https://en.wikipedia.org/wiki/File:Solar_evolution_%28English%29.svg https://en.wikipedia.org/wiki/File:Solar_evolution_%28Englis...