If I recall correctly, the upper stratosphere of Venus is highly reflective, so little IR from below gets out.
As for the pressure, a quick google search shows...
The atmospheric pressure at the surface of Venus is about 92 times that of the Earth, similar to the pressure found 900 m (3,000 ft) below the surface of the ocean. The atmosphere has a mass of 4.8×1020 kg, about 93 times the mass of the Earth's total atmosphere.
Thus the mass of air on Venus does approximate pressure. It's mostly CO2 down low, so it would be near liquid, very viscous like trying to walk underwater. Its gas envelope has reached equilibrium conditions.
From my google search, it appears the main reason that the atmosphere of Venus is thicker is because it is hot enough for the rocks themselves to leach out the carbon dioxide. In Earth's case, what is likely to happen is a warmer troposphere will result in a slightly thicker atmosphere due to water evaporation.(warm air can hold much more water vapor than cooler air.) This effect will likely counter any loss of atmosphere into space due to expansion. Especially since Earth has the benefit of having a robust magnetic field which protects the atmosphere from being stripped by the solar wind.
However, I will acknowledge that we just don't know all of the factors. It is possible that the meting of polar ice will disrupt the sea currents and make some regions cooler. This could then self regulate, by causing more snow and the ice caps would become bigger again.