I'm looking at designing a neo-Old Solar System version of Venus which is habitable. The following conditions hold:
- The cloud cover still exists, hiding Venusian civilization from the outside world and vice versa, though not necessarily with the same composition as in reality (see the next point) - though the albedo provided by the cloud cover is the more-or-less the same as in reality.
- Venus is habitable: beneath the cloud cover, Venus has an Earth-like atmosphere, a temperature in a hospitable range for humans (no runaway greenhouse effect), and for whatever reason - perhaps the cloud cover is composed of different chemical than in real life - acid rain is not a significant problem, except possibly as a rare natural disaster. (This is a huge break from reality, I know, but crucial to what I'm doing.
- The physical composition of Venus is broadly similar to Earth, and it has a nearly 24-hour day, in line with older calculations.
Given these conditions, which is actually more likely: an average temperature higher than that of Earth, or an average temperature lower than that of Earth?
The former is in line with common sense and older SF stories. My argument for the latter is that the cloud cover (point #1) gives the planet an albedo of 0.75, more than twice that of Earth, which when combined with a lack of runaway greenhouse effect (point #2) and a physical composition broadly similar to Earth (point #3), suggests to me that a habitable Venus should actually be colder than Earth, possibly in a permanent ice age.
The sort of setting I'm developing obviously doesn't demand strict scientific accuracy, but I'm wondering if there's any glaring flaws in my argument other than the false premeses of points 2-3.
Update: Just to make it clear, by "permanent ice age" I don't mean pole-to-equator glaciation, just something like what Earth went through not that long ago.