The lettuce thing is an analogy you apparently missed.
Anyway, you just don’t understand the cause and effect of play here.
Think about it like this. There is another feedback effect called albedo. Basically, this is just a measure of the earth’s reflectivity.
If we put a slab of ice on a dark surface in a box of glass and pointed a heat lamp into the box and cooled the slab via refrigeration, the amount of energy to keep the ice frozen would be some amount, let’s say 100 units of energy.
Now we add a heat lamp that uses 200 units of energy. The lamp shines in the box, but because the ice is white it reflects 95% of the energy of the lamp. The other 5% of that energy is absorbed by the ice. In order to keep the ice frozen, let’s say we have to add 10 units of energy to the refrigeration to keep the system in balance.
Now we add some CO2 to the box. Just a tiny amount. We observe that the amount of energy reflected back out of the box has changed by 1%. So now the lamp is adding 200 units, the ice is reflecting 95% of that energy, but CO2 has absorbed an additional 1%. Thus energy in and energy out are no longer equal. The energy cooling the ice is fixed, thus the system is now out of balance by 1% and the temperate in the box rises slightly. The ice very, very slowly starts to melt.
As soon as the ice melts to the point that the dark surface shows, the amount of energy absorbed into the system increases drastically leading to faster melting which leads to more energy absorbed which leads to faster melting and so on.
This is a simple example of a feedback loop and this is exactly what is happening to the earth…
So, the suns energy adds 100% of the energy received by the earth. 6% is reflected by the atmosphere, 20% is reflected by clouds 4% is reflected by the surface. This means that 70% of the sun’s energy is converted to longer wave higher energy as it reaches the ground. The latent heat now tries to escape via longwave radiation. The difference between what clouds reflect (20%) and what they absorb (23%) is slightly different. However, latent heat out has been until recently in the balance as most of that heat is radiated back into space. So the fact that clouds retain slightly more heat than they reflect is part of the overall balance of the system. In other words of the clouds reflected exactly what they retained, the earth would be getting colder as less energy would be converted to warmer longwave radiation.
Ok, so the system has been in balance. Now CO2 is increasing. The increase is not being offset by some reduction in energy in. As a result, more CO2 traps more longwave energy and temps slowly rise. This increases water vapor which in turn changes the % of energy reflected and the energy absorbed. The problem is, the % energy absorbed increases faster than the % energy reflected.
The point is, it was the change in CO2 that precipitated the change in clouds. Water vapor is simply magnifying that change of the amount of CO2, just like the darker surface under the ice magnified the effects of warming in the hypothetical about the lamp and the ice.
I fear somehow you’ll misinterpret all this, but it’s worth a shot.