Unfortunately, no one was sure whether interstellar clouds held enough water to do the trick — the water vapor in our own atmosphere makes it difficult for ground telescopes to measure
whatever water the clouds may contain.
Not exact matches
The really cold air can't hold all that
water vapor so the vapor instead condenses around any microscopic particles of dust, salt or
whatever else might be floating in the air and voila, you have a
cloud.
Whatever gives you a little lift — a cold drink of
water, the purr of your cat, the fluffy
clouds overhead — give it your focus and let that sliver of happiness register in your brain.
They do so because within these models the far more important radiative substances,
water vapor and
clouds, act to greatly amplify
whatever an increase in carbon dioxide might do.
Next, they assume a large (and unverified)
water vapor /
cloud /
whatever feedback on top of that, to give the 0.9 number.