You are quite right, if each 0.01 atm of CO2 added 1 deg C, then Venus with 90 atm of CO2 should be way way hotter than it is.

There are several explanations:

1. Venus does *not* receive 2x Earth insolation at the surface. It has an albedo of over 90%, if I recall, vs about 35% for Earth (all those clouds). Additional energy probably goes into heating the lower cloud deck vs the surface. Total energy received there is pretty low compared to Earth in full sunshine.

2. More importantly, energy radiated doesn't scale linearly with temperature, but with the FOURTH POWER of temperature. And it's energy we are balancing -- incoming with outgoing.

If you double the efficiency of something in the atmopshere that absorbs outgoing thermal radiation, you only increase the temperature by a factor of 1.18 (measured in Kelvin).

3. Furthermore, CO2 is only efficient at absorbing a limited slice of IR spectrum, and as you increase the temp you also increase the peak wavelength being emitted. CO2 has its peak absorbption at 4 and 15 microns. At 300 K Earth's peak emission is at something like 12 microns, and Venus at around 3 or 4 microns. As Venus gets hotter, a larger and larger share of its emissions aren't blocked.

So you're right, you can't just say that total mass of CO2 linearly translates to temperature, certainly not when comparing concentrations different by a factor of 10,000. Does that mean 100ppm to 200ppm has less than a x2 increase, probably. But zero or negligible? That doesn't follow at all.

>It can only mean that most of this warming is warming nites and winter areas. What it does NOT mean is that most warming is added to daytime and particularly to warmest period of the day temperature.

Please perform the following experiment. On a warm sunny day, lock yourself in your car and roll up the windows. Please report back to us on the results.