Piehole seems to forget that CO2 is the most important GHG on earth and is responsible for setting the temp levels. Solar is actually just an initiating force. CO2 is responsible for around 80% of the greenhouse effect. Without which the earth would be much much colder.
Radiative modeling analyses of the terrestrial greenhouse structure described in a parallel study in theJournal of Geophysical Research(Schmidt et al., 2010) found that water vapor accounts for about 50% of the Earth's greenhouse effect, with clouds contributing 25%, carbon dioxide 20%, and the minor greenhouse gases (GHGs) and aerosols accounting for the remaining 5%, as shown in Fig. 1. Thus, while the non-condensing greenhouse gases account for only 25% of the total greenhouse effect, it is these non-condensing GHGs that actually control the strength of the terrestrial greenhouse effect since the water vapor and cloud feedback contributions are not self-sustaining and as such, only provide amplification.
http://www.giss.nasa.gov/research/briefs/lacis_01/
Your quote is, of course, from the now famous, or infamous, paper that Lacis published on the GISS site five years ago. A paper that has been thoroughly critiqued by now and found wanting. I'll briefly summarize it. In 2010, Lacis, et al. used one of the better radiative forcing models then available to explore what would happen (according to the model) if CO2 were removed from the atmosphere. The results showed, that in the absence of CO2, clouds would disappear and this would lead to plummeting temperature (over time of course). This is what justified (according to the model, and Lacis' thinking at the time) the statement, often repeated by our own FC, that CO2 is the Earth's "thermostat" and "the most important greenhouse gas" despite it being not nearly so effective in its greenhouse properties as water.
I can now categorically say that this statement made by Lacis back in 2010 is wrong. CO2 is not the Earth's thermostat , and it is not by any means more important than water in moderating the Earths climate.
If one insists on choosing what is important to moderating,i.e., tending to keep the Earths temperature constant, it is of course the oceans and hence water. The thermal and mass exchanges that take place at the interface between atmosphere and ocean along with the Ocean's albedo, are extremely important. There are four other interfaces, however, that are important as well. One is the interface at the upper boundary of clouds, another is the interface at the lower boundary. A fourth interface that plays a critical role is that between the atmosphere and outer space. And of course the fifth important interface is that between land and the atmosphere. These five interfaces, their albedoes, and the mass and energy exchanges across them are the Earth's true thermostat, but only in the sense that they function together to keep the Earth's surface temperature from changing dramatically from day to night. Their function is to hold the temperature somewhere near the midpoint of what the range would be were there no atmosphere at all. The Sun and the planet's core comprise the Earth's furnace. What exactly is the Earth's "control knob", as Lacis put it, is yet to be determined, but there is almost certainly more than a single knob involved.
Although CO2 is hugely important to the existence of life on Earth, it plays only a minor and indirect role in affecting climate. Where then did Lacis, in his "Earth's Thermostat" paper, go wrong? Well, we could start with his model's not forming any clouds in the absence of CO2, and ignoring wind. The only clouds his model produced were those that formed from radiative forcing due to CO2, so when CO2 was removed the model stopped making clouds!!! Outside the model world, however, wind comes from uneven heating, and if solar heating and water is present, clouds will form, whether or not CO2 is present!
Lacis' model produced clouds when CO2 was present, but none when CO2 content was reduced to zero. The clouds produced by the model resulted in further radiative heating (positive feedback that is a ubiquitous feature needed to get exponential temperature rises out of smallish increases in CO2). But, in the model, clouds formed only when radiative heating from the greenhouse effect of CO2 was present. Cloud formation was dependent on CO2 being present! Clouds are impermanent; CO2 is permanent (until you instruct your model to remove it). Based on these results from the model's simulation of what would happen if CO2 was removed from the atmosphere, Lacis apparently felt justified in proclaiming that CO2 was the "Thermostat" and "control knob".
The result, naturally, of removing both CO2 and clouds, was that the Earth got unbearably cold, -20 deg C. (Presumably that is the average temperature, since during the model day it should have been damn hot. (I am assuming Lacis did not forget to turn on the Sun.) Everything reported is, by definition, true and correct in that Model's world. The results it produced, however, have nothing to do with the real world, where if all CO2 suddenly vanished, we would vanish but clouds would go on forming and playing their dual role of both cooling during the day and heating during the night -- assuming of course the Sun hadn't burned out.
The air over the desert has about the same CO2 content as the air over the prairie. The prairie is cooler during the day and warmer at night than the desert! The difference is not CO2, it is water vapor! If CO2 is the control knob it needs to be returned for manufacturing defects!
I my opinion, Hansen and Lacis formulated their problem incorrectly from the very beginning, and they have not recognized it yet. Atmospheric components such as water and CO2 alter the rate of heating and cooling, and can therefore only indirectly affect temperature maximum and minimum, as dictated by the length of time the "furnace", i.e., Sun and Earth's core, is on, and how much fuel is on the fire. (The main furnace is on during the day and off at night. The portable heater, i.e., volcanoes, are on and off on their own schedule. Think of these things, the next time, after a day of parching heat in the desert, you bed down for the night. Your going to need a blanket despite that nearly 400 ppm of CO2 that's up there!