There is a concise example of the greenhouse warming power of precipitable water (PW) available to look at today in central Canada. All I did to find it was to first spot an above-average anomaly, in this case a warm one, having a well-delineated shape that stood out in comparison with everything around it. On this map the image I picked has the shape of a caterpillar. One end starts just north of Manitoba, and the body then works its way southward where it curls around the southern tip of Hudson Bay, stopping in central Quebec:
The deep red part of this anomaly checks out at +18-21C on the color codes. There is a part of it in Manitoba that moves up one notch, to +21-24C, and some small bits in the most southern section also have this higher value. You will need a good amount of magnification to see them. We know from experience that the only thing likely to supply the energy needed for so much extra warming in a routine manner, on relatively short notice, and within a relatively confined area, would be the greenhouse effect of a powerful producer, one that also possessed a very special set of attributes attuned to accomplishing such a demanding task. Since we know there is such an agency in the real world, we’ll just hop over to the PW map and look for it:
Sure enough, there we see the same caterpillar shape, with almost exactly the same borders of delineation. The color codes will give us readings of 9-10kg in the two areas where the warmest anomalies are found, and 8-9kg elsewhere before fading away at the margins. (Again, use magnification for the best view.). The fit seems good from a shape standpoint, but what other connection is there? The rule I have repeatedly proposed, although it is not to be found anywhere in the publications of science, is that (outside of the tropical belt) any doubling in the amount (in terms of total weight per vertical square meter) of PW in the atmosphere of virtually any continental location, relative to whatever is average for that same location on that same day or the year, and apart from any change in effects due to other energy-related conditions, will raise the surface air temperature of that location by close to 10C. How good is this rule in today’s example?
We already know the current PW value and we already know the size of the anomaly. From that information, in accord with the rule, we can calculate that the average PW value for that day and location, all else being equal, must be no more than 2kg and most likely some fraction lower. Data that would reliably provide the desired information is nowhere to be found, but we can still do some improvising. I looked on today’s average temperature map to see what would best fit the caterpillar shape, and found a most welcome show of conformity centered around a curving line of -10C readings. You can see the line here, nicely shaded in deep blue:
Based on today’s anomaly, this means the average temperature for the area on all January 13s about 30 years ago was something less than -30C (-22F), which could be verified if necessary, but actually sounds about right. The temperature maps at that time would have then placed the area in a zone with deep magenta shading, just as it does today. Now look around anywhere on these maps, and see that whenever you find deep magenta temperature coding you will almost always find a coding value of 1-2kg on the corresponding PW map. I think it is safe to use that number for the current application, which makes everything fit quite well. One more thing—on this final jetstream-level wind map, look at the shape of the sloping curve of the air pressure isobars for this location. What does that tell you?
Carl