An explanation for why the Northern Hemisphere has warmed up much more than the SH during the last three decades. First, this is an established fact. I use information gathered from Today’s Weather Maps, a current copy of which is shown below. The numbers you see today for the two hemispheres, below the map, are not aberrations. They are are typical of the kind of numbers reported daily for both hemispheres over all of this past year and last year too, which is as far back as my memory goes. The SH has often been reported a few tenths lower than today, the NH sometimes higher. Other sources will give you monthly average differences that have a basically similar relationship to the dailies, but summed up as single numbers.
The world number, +0.7C, is a little higher than usual today. Most days will end up with an average of +0.5C, with a few more at 0.6 than 0.4. The apparent 5C average over 31 years, away from the 1979-2000 baseline period, is derived from adding up all the hot and cold anomalies for each day of the year, pixel by pixel. It ends up being perfectly consistent with the long-term trend that has been averaging +0.17C per decade for the past three decades, and more, as we see on the next chart. What this tells me is that daily anomalies of all kinds do a pretty good job of laying the groundwork for longer-term anomalies, which makes good sense. If you can calculate all of the anomalies, both long and short, with great accuracy, what other outcome can be the result? I think this is an amazing feat of technical accomplishment, the implications of which must be taken seriously.
Now back to the hemisphere anomalies, which I am assuming are just as accurate as the worldwide anomalies. One of the differences you easily detect today is that NH has far more extreme anomalies than the SH, both warm and cold. This is how they appear every day, and both kinds of extremes are for real. There is no way to add everything up by simply eyeballing the map, especially with so much dimensional distortion to factor in. For some reason the NH is more prone to generating extremes of both kinds than the SH, and we should want to know why. We should also want to know why the net outcome for the all the extremes we see each day always seems to balance out fairly evenly. Neither kind of extreme ever seems to gain the upper hand on any one day in spite of the way they keep bouncing around in all shapes and sizes.
There are two questions we want answered here. One is why the NH is warming so fast but not the SH. The other is how to explain the extreme anomalies of both kinds in the NH but not the SH, with the exception of the polar area comparisons. Are the answers related? The possibility that I find most intriguing places most of the responsibility on the formation of atmospheric rivers (ARs) and the fact that they are all exclusively loaded with precipitable water (PW). These rivers exist as phenomena found only at high altitudes, and nowhere else. The PW they carry is highly concentrated at the start, then gradually tapers off as river flowing progresses. I am absolutely convinced that all of the PW on board each AR generates an extremely powerful greenhouse energy effect that is immediately realized on any given surface below whenever a concentration is passing over. Here is an important point, one that I need to stress in a more open way: the character of the actual greenhouse impact on any given surface is considerably dependent on the physical nature of the surface, its geographical location and the normal strength of its ambient humidity, always present. Each of these considerations will be separately reviewed.
In order to understand where ARs come from, where they go and how their lives unfold you must spend some time studying the 5-day animation chart at this website: http://tropic.ssec.wisc.edu/real-time/mtpw2/product.php. One thing to note is that there is very little difference in the number of ARs originating in each hemisphere, or the total volume of their PW content, or many of the details about the way they move. The same impression can be gained by looking at one-day snapshots, like the one we see today on the weather maps:
There is one key difference, easily observed: it turns out that ARs in the SH do the bulk of their flowing over open ocean water, while in the NH a far higher percentage of their lifetime activity is over land. Oceans have a natural tendency to absorb and store for long durations much of the newly-added energy that emanates from ARs when they become enlarged, eliminating a good share of its greenhouse potential on air temperatures, or on temperatures of the surface itself. Land surfaces respond in a completely different way, by re-emitting far more incoming radiation back into the atmosphere after relatively brief delay periods. I think this factor alone can account for much of the actual difference between the continental air temperatures. We can visualize the greenhouse energy effect of the PW being carried by the ARs in each hemisphere, falling upon surfaces on the receiving end that are of maximum contrast, and to not much else. (To be continued.)
Carl