[gshubert17]

Due to stellar evolution, the solar constant is at its highest on a geological timescale.

https://archive.org/details/nasa_techdoc_19820009158

Back in the Mesozoic Era, the Sun was about 2% cooler than it is today. The extra CO2 back then added a helpful (for most life) greenhouse effect. Now, both the relatively high CO2 level and the rapid rate of increase are unhelpful.

[jessaustin]

That link performs a calculation based on some fairly back-of-the-envelope physics assumptions. Its conclusion:

Roughly one-half of the solar luminosity increase occurs during the last 2 billion years but there is no evidence for a parallel increase in the Earth's mean surface temperature. Indeed, isotopic studies of the Precambrian samples by Knauth and Epstein (ref. 12) indicate that the mean surface temperature has been decreasing during this time. Clearly, there is a need for further studies of the effects of crustal movements and volcanism, biological activity, etc. on the long-term evolution of the Earth's climate. At present, it appears that the effects of solar evolution are still buried in the "noise" due to other uncertainties in paleoclimatic models.

Is there anything since 1981 with more definitive conclusions? Is there any study that has attempted to measure sun output directly or indirectly, rather than simply calculating output based on the sun's age?

[Jweb_Guru]

Thank you. Nothing annoys me more than people who bring up the fact that CO2 used to be much higher without mentioning that the sun was cooler. It leads to a very misleading picture.