OK, some quick science (explained well here at this site). The atmosphere of Venus is utterly inhospitable for life as we know it: too hot, too much carbon dioxide, and almost completely lacking in water vapor. And all three characteristics are due to a combination of two factors: the lack of a magnetic field on Venus, and the solar wind (which is also considerably stronger, that much closer in). Because there is no magnetosphere, the solar wind interacts with the Venusian atmosphere much more strongly than it would otherwise; this has the effect of stripping out hydrogen from the atmosphere. No hydrogen = no water vapor. No water vapor = no hydrosphere, pretty much no opportunities to turn carbon dioxide into something else.
You’re probably remembering this situation as the ‘runaway greenhouse effect:’ an argument that we used to hear a lot more of in the context of global warming before it became clear that we were unlikely to replicate Venusian conditions* unless we first figured out how to turn off Earth’s magnetic field**. At any rate, that’s why Venus is so danged hot.
It is not because of aliens, Mister Gore. (more…)