With no water left on the surface, carbon dioxide built up in the atmosphere, leading to a so - called runaway greenhouse effect that created present conditions. (sciencedaily.com)
There is NO observable, runaway greenhouse effect on Venus at 1 bar,... ONLY a factor of temperature increase related to the ratio of solar distances. (hubpages.com)
A clearer picture of volcanism on Venus and its history could help to explain how the planet's runaway greenhouse effect got going. (scientificamerican.com)