Carl’s theory makes certain claims about the greenhouse energy effect of precipitable water (PW.) One primary claim is that, with all other conditions being equal, and subject to specific limitations, any doubling of the weight of PW’s atmospheric content will add about 10C to surface air temperatures directly below, or the reverse. Limitations regularly occur within the tropical belt and over large expanses of open water; otherwise the claim is intended to be unequivocal if all the other conditions that contribute to temperature changes are equalized. Some of these other conditions are important and have effects that are difficult to evaluate for purposes of equalization. The albedo effect of cloud cover belongs at the top of that list. Extreme variations can regularly be noted, leading to cooling effects that range from practically none at some times to numbers great enough to more than offset the greenhouse warming effect of the PW that produced the very same cloud cover.
According to one tenet of Carl’s theory, the greenhouse energy output of PW does not significantly change when vapor molecules have condensed into clouds. It keeps on warming as before. What does change is by variation in the amount of cooling due to the albedo effect of new cloud formation. The greenhouse effect remains relatively constant at all hours of the day in all non-tropical latitudes and without regard to seasonality. By contrast. the albedo effect is only realized when the sun is shining, which is only half the time, and even then it still depends in part on a tradeoff between the angle of radiation input and the number of hours of sunshine on each day. In the tropics these two things are nearly stable all year long. Beyond the tropics seasonality is always important and the tradeoff appears to favor cooling from a higher angle of radiation over warming from extended hours of sunlight. Albedo is thus at its maximum effectiveness in the mid-latitudes in mid summer, which is where things stand right now in the north and will remain for awhile.
We can illustrate the relative strength of this effect by opening three maps showing current happenings over a large territorial spread. One will show cloud cover plus rainfall intensity, one has PW content across the atmosphere, and the third has all the resulting surface temperature anomalies. The high-altitude streams of PW concentration that produce copious rainfall practically always cause total PW content to be well above its historical average for the day and therefore a nominal source of planetary warming. But what is today’s reality? When you do the comparisons on these maps, sticking mainly to non-tropical and non-Arctic land surfaces, I think you will see a close association between areas that have heavy rainfall, high PW values and cool anomalies, rather than warm ones, all at the same time. Then look for nearby areas that have the same signs of high PW but no rain clouds and see how much higher the anomalies are. These anomaly differences should give you a rough idea of how powerful the albedo effect can be when clouds are thick and maybe also wetter rather than icy on their tops, as researchers have lately been proposing.
Some rainy or cloudy areas to pick out include the region to the east and north of the Great Lakes, the US southeast, north Texas, southern Mexico, the Canadian northwest and also across the Atlantic in eastern Europe. They are all associated with cool anomalies and relatively high PW values. In fact, as an offhand observation, I can see very few cool-type anomalies being caused anywhere at all by below-average PW values, similar to those that are so common in the northern winter season, or currently in Antarctica.
Carl